DISCLAIMER_Throughout this publication, reference is made to a number of pesticides (herbicides, fungicides and insecticides) which have been used either commercially or experimentally in hemp production. It should be emphasised that with any pesticide application the relevant legislation (Health and Safety at Work Act 1974; Poisonous Substances in Agriculture Regulations 1984; Food and Environment Protection Act 1985; Control of Pesticides Regulations 1986; Control of Pollution Act 1974; Plant Protection Products (Sustainable Use) Regulations 2012 etc.) and the Product Label Recommendations must be adhered to._

1. INTRODUCTION

1.1. HEMP (Cannabis sativa L. spp.)

Hemp (Cannabis sativa L.) has become interwoven over time into human history. It’s estimated that purposeful human cultivation of hemp dates back as far back as 6,000 BCE. Logically, its use dates back even further >10,000 years ago. Due to its long concurrent history with humans, there are a vast number of cultivars for a range of uses. Traditional use of hemp has been for its fibrous stems to make materials such as textiles and ropes. This versatile crop has also been cultivated for its medicinal and nutritional properties too. Hence, there are tall fibrous plants for fibre production and short, stout bushy plants that produce lots of flowers and seeds for food and medicinal use. Currently, hemp cultivars are still utilised for all its historical uses. However, there is now a growing interest around hemp for a whole range of exciting novel uses. Hemp fibres can be used in biocomposite materials such as insulation sheets/panels, expanded foams and even mixed in with a binder to make hemp concrete. Major car manufacturers are already using hemp biocomposites for car components such as linings and parcel shelves. Additionally, hemp is made into horticultural matting. What is more, hemp also shows promise as a source of bioenergy. Hemp straw can be baled or briquetted and combusted to produce energy, whilst the oils extracted from the seeds can be used to create a biodiesel, the fibre can also be used to make cellulosic ethanol.

While fibre and seed are the main products of hemp, there is a growing interest over the valorisation of hemp secondary metabolites. Hemp leaves and flowers are rich in unique bioactive secondary metabolites, such as flavonoids, terpenoids and cannabinoids. These secondary metabolites can be utilised for a range of uses, from biopesticides to pharmaceuticals. Hence, plant breeders have been developing new cultivars that can be harvested for both multiple uses, such as harvesting vegetative material for isolating secondary metabolites and fibre for biomass feedstock. These cultivars are termed dual hemp.

Along with hemp's extensive list of uses, it has also been suggested that it is an ideal candidate for remediating degraded land, can sequester large volumes of carbon (1 ha of industrial hemp can absorb 15 tonnes/ha of CO2), and requires very little agronomic input. All this makes it an attractive crop for diversifying farms.

2. PRE-PLANTING

2.1. SITE SELECTION

Hemp will grow on marginal lands with minimal input. However, the crop will grow better on good soils with good agronomic management. Site selection may vary depending on the desired end goal of your cropping system and whether you are planting to utilise marginal fields or looking to remediate contaminated soil. In this volume we will highlight conditions for optimal growth of industrial hemp.

2.1.1. SUITABLE SOILS

Hemp prefers well drained and aerated soils with silt/loam textures (40% sand, 40% silt, and 20% clay). The soil should also have a good level of water holding capacity. Hemp will grow in soils ranging between pH 5.0-7.5. However, optimal growth is observed between pH 6.0-6.5. Acidic soils should be avoided. It should also be noted that hemp is good at accumulating heavy metals, thus sites with high levels of heavy metals such as ex-waste sites, and sites exposed to heavy industrial fallout should be avoided if there is evidence of high heavy metal presence in soil test analyses. Sites with heavy metal presence should especially be avoided if the end use is for human consumption.

2.1.2. WATER AVAILABILITY

Hemp requires high moisture levels throughout the growing season. Hemp requires a good level of soil moisture for seed germination and additionally there’s a particular need for water during the first 6 weeks of growth whilst the seedlings are establishing. After the plants have produced their large tap roots and are well established, plants can endure drier conditions. Hemp roots can penetrate the soil up to 2–3 m to extract moisture, depending on soil conditions. However, severe droughts can induce maturity early and lead to stunted crops. Optimally, hemp requires 630 to 750 mm of rainfall per annum. It has been reported that hemp yield strongly depends on the amount of rainfall between June and July and depends on good levels of moisture during their vegetative growth period. Water requirement and uptake varies depending on the hemp cultivar, environmental conditions, and management practices.

2.1.3. TEMPERATURE

Temperature plays an essential role in hemp production, which is distinct throughout different growth stages. Hemp grows best in temperate climates but will grow in a wide range of environmental conditions. Optimal temperatures for germination under field conditions is between 13.5-18.5°C. However, hemp will still germinate at lower temperatures. Germination appears to be more sensitive to higher temperature with negative effects on germination greater when exposed to heat stress. Some young seedlings (8–10 leaves) can tolerate temperatures down to −5°C. Hemp seedlings grow best when the mean daily air temperatures are between 16-27°C.

2.1.4. PHOTOPERIOD

Hemp is a short-day plant. Day length affects the hours of light received by the plant and influences the growth and productivity in hemp cultivars. The shift from the vegetative to flowering stage in hemp is dependent on day length and variety. Some hemp cultivars can initiate flowering irrespective of day length, while others require shorter days to transition to the flowering stage.

2.1.5. SITE ACCESS

Sites are generally harvested with adapted standard farming machinery. Thus, hard tracks will be needed for access to the field.

2.1.6. SUITABLE LAND AREA

As with all crops, there is an economy of scales. The more land planted, the more economical the process becomes. However, depending on the reasoning for planting lower areas of land can be planted. Hemp is a suitable candidate crop for soil remediation. Thus, polluted, or marginal lands can be planted, however, lower yields are to be expected. Yet, if incorporated into a rotation plan, planting hemp can improve the soil for the next crop. However, unlike most other energy crops, hemp is not perennial. Thus, it’s a good idea to select a small plot of the farm with optimal growth conditions for testing in year 1 to learn and develop the skills needed to maintain the crop, and then scale up from there.

2.1.7. LOCATION IN THE LANDSCAPE

Depending on the cultivar of hemp grown, the height of the crop can vary from 1.0-3.5m. However, most fibre cultivars will grow no higher than a crop of maize (~2.0 m) whilst the shorter seed bearing cultivars will be around chest to shoulder height. Hence, visually the crop will be very similar to a standard arable crop and will not cause visual impairment to local environments. It should be noted that regulations may differ depending on which country the crop is to be grown. Restrictions may include not being permitted to be grown alongside roads, public rights of way, or near schools.

2.1.8. CROP ROTATION

Crop rotation is an important aspect of modern farming. It is vital for improving soil health and disrupting weed and pathogen cycles. Hemp offers a suitable opportunity as a break crop when incorporated into crop rotation plans. Hemp has deep penetrating tap roots and a large proportion of hemp biomass is in the roots. Thus, hemp has been shown to increase soil organic matter and improve soil structure by increasing soil aeration while simultaneously reducing soil erosion by increasing soil aggregate binding.

Growing the same species of crop in the same field over multiple growing seasons encourages the build up of its soil-borne pathogen population levels. Hence, crop rotation is essential to disrupting disease cycles. Hemp has been shown to reduce pathogen abundance in the soil, specifically Verticillium dahliae, Columbia root-knot nematodes (Meloidogyne chitwoodi) and northern root-knot nematodes (Meloidogye hapla). All of these economically important pathogens are currently observed in the UK, other than Columbia root-knot nematodes, which are found in most countries on the European mainland. The high planting density, fast growth and rapid canopy closure after emergence make hemp very competitive against weeds. Hemp can successfully suppress weeds in the field without herbicide use, thereby reducing production costs. Additionally, this also breaks the weed cycle for the next season. Hemp's ability to suppress weeds and soil pathogens reduces the amount of pesticides needed for the next crop grown in the rotation. It should be noted that hemp can successfully do this, however, not all sites and climatic conditions favour this. Redshank and some other annual weeds can persist, especially if hemp is grown on the same site in successive years without the use of herbicides. Further highlighting the importance of crop rotation.

With hemp's ability to improve soil quality and reduce pest population levels, it is no surprise that hemp can improve the yields of crops grown in rotation with hemp. Hemp rotation has shown increased wheat yields and a positive effect on soybean growth. Further work is required to show the effect of hemp rotation on other common crops.

2.2. SITE PREPARATION

Currently, there are no pesticides prescribed for hemp in the UK and Ireland. This is due to hemp's relatively recent re-appearance in modern agriculture in addition to its fast growth and competitive nature. However, to give the plant the best chance of maximising its yield potential, site preparation should be undertaken with the utmost care.

2.2.1. SOIL TESTING AND MANAGEMENT

Soil testing should be undertaken before planting. The pH and Soil Nitrogen Supply (SNS), phosphorus (P), potassium (K) and magnesium (Mg) indices should be screened for and should be adjusted during the site preparation stage if needed. There are multiple soil testing companies which can offer services with in-depth soil analysis and reporting. Even field level analyses can be provided to help carry out targeted nutrient application.

Based upon the results of the soil tests, nutrient or lime application can be carried out to adjust the levels to the optimal conditions for hemp. It should be noted, unnecessary fertiliser application may only encourage weed competition during establishment.

Additionally, soil microbial biomass and community profiling can be employed. Mycorrhizal fungi are able to encourage the successful establishment of hemp and support hemp to grow in contaminated or stressful environments. Testing can give an idea as to whether supplements may be required for when planting commences.

What is more, baseline soil analysis can be used for identifying soil carbon stores.

https://ahdb.org.uk/knowledge-library/soil-and-forage-testing-companies

2.2.2. FERTILISATION

Hemp requires precise fertilisation management. Studies have found that too much or too low a fertiliser application can result in self-thinning and reductions in yields. The total NPK requirements for hemp is 110 kg N/ha, 80 kg P/ha and 140 kg K/ha. The following sections will clarify the N, P and K requirements individually. It should be reiterated that soil tests should be carried out before applying fertiliser to the land as the soil could possibly have sufficient NPK levels.

2.2.2.1. NITROGEN (N)

Rates of N offtakes are observed at ~160 kg N/ha for biomass and ~40 kg N/ha for seed, totalling ~200 kg N/ha. It is important to provide sufficient nitrogen for the rates of nitrogen use. Low application of N (80 kg N/ha) terminates growth prematurely, whilst a high application rate (200 kg N/ha) will result in the plants competing for light. This results in fewer plants/m2 and lower yields. It is suggested that between 110-150 kg N/ha should be applied. However, the application rate should be determined on the soil resources available and the N deposition rate observed locally. Furthermore, application prior to planting appears to be just as effective as split application. Split application is where a percentage of fertiliser is applied pre-planting and then the rest is applied after germination, during the rapid growth phase. Split application has potential risk aversion benefits, such as inability of plant to uptake N due to stress, or unforeseen weather events, not overwhelming seeds, and less encouragement of weed growth. Therefore, current advice for split application is as follows, 70% at planting and 30% at elongation/rapid growth phase.

2.2.2.2. PHOSPHOROUS (P)

P is an essential macronutrient essential for all growth stages of hemp but its demand changes over the crop growth cycle. P is essential in early growth stages due to its role in imparting strength and resistance against pests. P uptake then gradually increases as the plant matures. Total phosphorus uptake by plants ranges from 25-67 kg P/ha depending on variety and yield. Suggested P application is therefore 30-80 kg P/ha. However, applying excess P at planting can cause additional stress. Application should be based on soil available resources and predicted yield.

2.2.2.3. POTASSIUM (K)

Hemp appears to be less responsive to K in terms of yields, yet it has been shown to be important for fibre quality. In addition to this, uptake of K is substantial. Overall, a total uptake of P in hemp has been observed at ~211 kg K/ha. Rates of 140-175 kg K/ha are recommended, again, dependent on soil resources and yields.

2.2.2.4. OTHER NUTRIENTS

Ca, Mg, S, Cu, Mn and B have been regarded as important for the healthy development of hemp. In particular, Ca, Mg and S. These can all be observed in the soil test results and can be altered accordingly.

2.2.2.5. DIGESTATE

Split application of liquid phase digestate (LPD) and solid phase digestate (SPD) has been shown as a suitable alternative to mineral fertilisation. Rates of application should match the required NPK levels described above. Due to prolonged nutrient release from SPD, reduced negative environmental impacts are observed when compared to mineral fertilisation.

2.2.3. PLOUGHING AND CULTIVATION

Seedbed preparation is extremely important for successful hemp cultivation. Hemp is very sensitive to soil structure, requiring a well prepared seedbed. The best way to prepare the seedbed is by treating the soil as if you were cultivating sugar beets or spring wheat. Where permitted, autumn ploughing at 20 cm is advised followed by cultivation using a rotavator/power harrow to create a stale seedbed. If it is not possible to leave the field fallow over winter then it can be carried out as early as the local regulations and weather permits in late winter/early spring. The stale seedbed can then be sprayed off with an appropriate herbicide for the weeds that are observed germinating. 10-14 days after this the field can be rotavated/power harrowed and rolled a final time before planting. It is optimal to get good soil to seed contact, this is achieved by creating a fine tilth within the seeding zone (1.5-4 cm) and a medium-to-large aggregate size on the surface which helps to reduce evaporation.

2.2.4. EXCLUDING VERTEBRATE HERBIVORES

Birds are very fond of eating hemp seeds. Therefore, precaution should be taken to keep birds away during the period before emergence. Scarecrows, bird of prey kites, laser scarecrows, propane cannons and if applicable bird nets can be applied. If none of the above are already available to you then the most effective, cheap option such as the kites will suffice.

Although hemp is not a food of choice, deer grazing can be an issue for hemp. Deer fencing is not a suitable solution due to its expense. If deer are observed grazing on hemp and causing significant damage, then a Garlic Barrier can be used. Applications of 1-2 l/ha should be made across the whole crop and the spray will remain effective for 12-14 days. It should be noted that it should not be applied if rain is forecast in the next 48 hours. Re-application may be required if it rains.

Rodents, such as rats and mice, can strip the stems of their ‘bark’ for nests. Additionally, rabbits can eat the young plants and strip the bark of older plants. Again, if this is of serious concern then a Garlic Barrier can be deployed.

2.3. VARIETY SELECTION

2.3.1. VARIETIES

When selecting hemp varieties it is key to understand the local market for hemp and thus know the intended end use. For example, are you looking to produce a fibre for animal bedding, building material (e.g. hempcrete) and textiles, or do you want to harvest the seed for oil or a food product? Or both? Therefore the question needs to be asked, will you be harvesting the seed alone, biomass alone or do you intend to harvest both? Additionally it is imperative to understand your local climate and growing season, this is because varieties that have shorter growing cycles (early flowering) will cease stem growth and set seed earlier. By contrast, varieties with longer growing cycles (late flowering) continue stem growth late into the season, which is beneficial if the intended end use is for biomass. As set out below, there are varieties that can be used for both, depending on the climatic conditions.

At the time of writing there are 100 varieties of EU registered hemp. All EU registered hemp varieties can be found within the EUPVP - Common Catalogue Information System (https://ec.europa.eu/food/plant-variety-portal/). Search filters to be set as UPOV Species = Cannabis sativa L., and Variety status = Registered. Some of the most used hemp varieties in the UK and Ireland (varieties highlighted with ‘*’ below), and the rest of the EU are listed below.

2.3.1.1. SEED PRODUCING

• Finola* Grain specific cultivar in a short, auto-flowering and early maturing crop. Finola grows best in continental and temperate regions and was one of the first grain specific varieties for higher latitudes.
• Henola* Grain/oil variety, characterised by a good seed yield with high oil content and shorter plant height – up to ~2m. In addition to a shorter vegetation period, around 3 weeks shorter when compared to Białobrzeskie. Henola seed contains a favourable fatty acid ratio.
• USO 31 A variety commonly used in Europe, USO 31 is a good compromise between an early seed harvest and a high fibre crop. USO 31 is versatile, this seed grows well in temperate zones of the Mediterranean as well as in Central Eastern Europe. Low in phytocannabinoids content.
• Białobrzeskie* Białobrzeskie is characterised by a high yield of seeds, and abundant high quality fibres. A staple variety that has been grown for textiles since the 1960s. It is also popular with CBD extractors for its cannabinoid profile.
• Félina 32 One of the most popular varieties to be grown in Europe. Its popularity comes from its tall stalks and abundant production of flowers that are rich in CBD, when compared to other cultivars. Félina 32 can branch when planted densely. Also, Félina 32 performs best in continental or oceanic conditions.
• Fédora 17 A choice cultivar among Central European growers, this variety is successfully grown across the entire European Union. Fédora 17 produces impressive seed yields whilst also offering the option of straw/biomass production. Mainly bred for the production of hemp oil from the seed. Can also be used for the flowers. The flowers can reach high levels of cannabinoids for CBD production.
• Earlina 8FC Earlina 8FC is one of the few varieties bred specifically for grain production in Northern Europe. It is one the earliest grain varieties to mature. It produces large yields of seed with over 30% oil, 25% protein and moderate levels of CBD. Its short growing cycle is adapted to late-spring and early-autumn conditions. Best suited for climates with lower levels of humidity and shorter growing zones.
• Férimon Férimon performs best in northern latitudes where it displays high seed yields and produces significant biomass for fibre. Férimon expresses early maturing, high seed yield and good fibre content. It has also shown adaptability to Central and Southern Europe. Férimon grain is widely used in agri-food and cosmetics.
• Orion 33 Orion 33 was bred for grain/dual cropping. It’s an early flowering variety with an extended vegetative cycle. Orion 33 can produce good grain yields in more southern latitudes. The seeds produced by Orion 33 have a high protein content. Additionally, it can be grown in fields with low broom rape infestations with no drop in yields, all while slowing the development of the parasite.

2.3.1.2. FIBRE PRODUCING

• Tygra Tygra produces a high yield of good quality fibre. Tygra also has potential for a grain yield of up to 1 t/ha. A stable variety with a relatively short vegetation period.
• Fibror 79 A variety that’s bred for its rich fibre content. The hardy Fibror 79 can be grown in any geographical location, including areas with high heat, humidity and rainfall. The plant displays a long and straight yellow stem, along with yellow-green foliage as the plant matures. It also produces flowers that contain a lot of CBD.
• Futura 75 Grows in both northern and southern climates. In northern climates greater yields of fibre content are observed. In southern climates extended growing cycles are seen, resulting in a fair seed yield, good straw/biomass yield and flowers with elevated levels of CBD.
• Futura 83 Certified in 2021, it has a late-flowering cycle that makes it ideal for biomass production. The plant grows best in southern latitudes in high humidity areas. Futura 83 has long straight stalks and produces good fibre yields. It also yields edible seeds, CBD extract from the biomass whilst producing satisfactory quantities of bales.
• Santhica 27 Bred to produce large fibre yield, this variety grows best in Northern Europe in areas with higher humidity levels. Santhica 27 is not commonly harvested for seeds, so seed conducive humidity levels aren’t necessary. Additionally, flowers from Santhica 27 also contain significant CBG levels and low THC. While generally recommended for Northern Europe, Santhica 27 has also been cultivated in Spain.
• Santhica 70 A variety dedicated to fibre yield, however, can produce some seed. Displays a larger geographical range than Santhica 27 and is usable in Southern Europe, as well as Northern Europe. Santhica 70 is low in the cannabinoid CBD. The outdoor production follows a medium-late cycle.
• Muka 76 A late flowering fibre variety with an even larger geographical range than Santhica varieties. Developed for processing, Muka 76 is said to be easier for fibre and hurd separation in post-processing methods. Muka 76 produces large amounts of foliage and good yields of fibres and shives
• Rajan Rajan is characterised by high biomass production. A mid-early variety. Can grow over a large latitudinal range.
• Kompolti The oldest registered variety in Europe. Kompolti is late maturing and is a very good producer of fibre. It can also produce high yields of CBD. Kompolti shows high vigour and wide adaptability to different environments. It was originally developed for fibre, however, is now used for the production of inflorescences and CBD. Further information about the varieties listed are found in table 1 and on the EUPVP - Common Catalogue Information System.

Table 1 - Based upon the Hempoint 2023 Seed Catalogue table, Hempoint state data was taken from the variety breeders and online resources. Missing values were filled in utilising Hemp: Industrial Production and Uses (CABI, 2013). It is important to note that hemp growth is highly dependent on climatic conditions, therefore the values obtained are likely to be different to those stated in the table below.

2.3.2. LIST OF SUPPLIERS

2.4. PLANTING MATERIAL

2.4.1. PLANTING SEED QUALITY

EU authorised seed should be obtained from a certified vendor. Reliable seed vendors will have a history of working with the particular seeds and will be able to provide reliable germination rates from data they have acquired over several years of working with the seed of the different varieties they provide. Alternatively, if you want to check seed viability yourself, you can carry out a germination test or a tetrazolium-based viability test. These can be carried out by a local registered testing laboratory. Laboratory testing would be recommended. However, a germination test is quite simple to carry out yourself. Firstly, take a paper towel, fold it in half soak with water and place in a germination container/larger plastic box/tupperware box. Take 100 seeds and place them with even spacing on the folded damp paper towel, cover with another soaked paper towel, close the container and place in the fridge for 7 days. Remove from the fridge and place in a dark area between 20-26°C. It is important that the seeds are kept damp throughout this period, therefore should be checked regularly and sprayed with a water mister daily if required. 7-14 days at 21°C should be allowed for germination. After 14 days, the number of seeds that have germinated should be counted and the germination rate calculated as a percentage of seeds sown.

2.4.2. PLANTING MIXTURES

Currently there is no advice on planting hemp as multi-variety mixed plots. Hemp, in the wild, can grow in vast monocultures. However, it is known throughout agricultural systems that multi-variety cropping systems are more resistant and resilient to disease, pests and environmental stress.

2.4.3. PLANT BREEDER’S RIGHTS

All improved commercial varieties are protected by EU and/or UK Plant Breeders’ Rights. In practice, this means that it is illegal to produce propagation material for self-use or sale from protected varieties. Generally, therefore, seeds for propagation should be produced by specialist growers.

2.4.4. PLANTING MACHINERY

Standard grain seed drills can be used to plant hemp seed. Alternatively, a planter using grain plates can be utilised.

3. PLANTING

Hemp seed should be planted into a firm, fine and clean seedbed. Additionally, good soil to seed contact is required, this can be achieved by rolling after drilling. This is usually necessary and beneficial on lighter and stony soils, reducing moisture loss from the soil. Heavier soils can be rolled if there’s a risk of moisture loss but it is essential to avoid seed capping. Seed drills are primarily used for seeding hemp yet most seeding equipment is applicable. Imperatively, it is important to monitor seeder output to avoid seed cracking. This can be avoided by using lower air volumes because seeds can crack in the manifolds when the pressure is too high. Additionally, field germination and mortality rates should be considered when calculating seeding rates. These can be advised upon by the seed supplier. Finally, although a firm seedbed is a positive for hemp, excessive compaction should be avoided, such as wheel tracks or other forms of soil compaction.

3.1. TIMINGS

Hemp germination rates are correlated to soil temperatures. Thus hemp should be seeded into warm soil of at least 8-10°C in the top 5 cm. The soil should remain above 8-10°C for at least 2-3 days. Usually this is observed between late April – mid May in the UK and Ireland. In some areas of Europe this may occur earlier in the year. It is important that there are no cold snaps after planting. Additionally, avoid seeding before an abundance of precipitation is anticipated. This can wash away seed and soil, and expose the seed to birds. Best practice is to seed after a heavy rain rather than before.

3.2. PLANTING DENSITY

Planting density depends on the end use. Seeding density for seed production would usually be around 100-125 seeds/m2. Seeding density for fibre production would usually be double that for seed. Planting around 200-300 seeds/m2. Planting is usually measured for hemp seed as kg/ha. Standard seeding rates are 35 kg/ha for grain producing varieties and can be up to 70 kg/ha for fibre producing varieties. However, this will be dependent on the cultivar being planted, therefore, refer to the seed supplier or breeder for more specific details on planting densities.

3.3. PLANTING DEPTH

When drilling or seeding hemp be sure to seed shallow, 1.25-4 cm. In a dry year do not seed deep trying to find moisture. Even though hemp seeds are moderately large, hemp will struggle to emerge from deep seeding. However, if seeded too shallow birds will predate on the seed or they could be washed away in heavy rain.

4. POST PLANTING ESTABLISHMENT

There is very little to be done with hemp post planting. Hemp grows fast and reaches canopy closure quickly.

4.1. NUTRITION & FERTILISATION

Fertilisation can be split however further testing on this is required. Some issues are seen with applying excessive fertiliser with the seed, thus it is an option to explore if low levels of emergence are observed.

4.2. WEED CONTROL

There are no authorised pesticides for the control of weeds in hemp cultivation. Additionally, hemp is a strong competitor for nutrients and light, quickly outcompeting any weeds in the field, as long as site preparation has been undertaken thoroughly.

4.3. DISEASE & PESTS

Infections of the flowers/buds to watch out for are powdery mildew or mould fungi growing on the flowers and mites.

Leaf diseases observed in hemp include powdery mildew, Alternaria leaf blight of hemp, and leaf sooty mould. Leaf sooty mould is encouraged by aphid infections, where the aphids excrete a high sugar containing liquid which acts as a nutrient source for the sooty mould fungi.

Stem diseases that are found in hemp include stem canker caused by Fusarium oxysporum and Fusarium solani, stem rot caused by Fusarium sp. and Pythium sp., crown rot caused by Pythium aphanidermatum, and crown and root rot caused by bacteria.

Diseases affecting hemp root include hemp root rot caused by Fusarium sp., root rot caused by Pythium myriotylum, root knot caused by the root-knot nematode, and ectoparasitic nematodes.

Systemic diseases of hemp affecting the whole plant include systemic wilt caused by Fusarium oxysporum, witches’ broom on hemp caused by nonculturable bacteria Phytoplasma, hemp streak, mosaic and hop latent viroid, hemp leaf roll, and beet curly top virus.

Further information on identifying, diagnosis and control/treatment of certain diseases can be found in the book ‘Diagnosing Hemp And Cannabis Crop Diseases’ (Shouhua Wang, 2021).

5. HARVESTING

Hemp harvesting is usually carried out using adapted arable machinery. Depending on what variety is grown and for what purpose, there are different methods for harvesting hemp.

5.1. TIMINGS

Hemp can be harvested from late July, early August. This is dependent on when the crop was planted, the climate and the end use of the plant - seed/grain, leaves, straw, fibre or for multiple uses?

A method for determining whether seed or dual-purpose hemp crops are ready for harvest is through seed moisture content Seed moisture content determines straight combine timing. For Finola it is advised to start harvesting when moisture content of the seed is 12-15% and 14-20% for taller grain varieties.

Fibre only hemp is usually harvested in the early flowering stage. This is between bloom and seed set, when the lower leaves of female plants begin to yellow. This is the stage when the fibre volume in the plant is at its maximum. It should be noted, harvest timing may vary by processor.

5.2. HARVESTING METHODS AND MACHINERY

Below two harvesting methods will be explained, one for separately harvesting the top and the rest of the plant and one for harvesting the entire plant.

5.2.1. TOP HARVESTING

Top harvesting is a method by which you pass over and cut the top part of the plant off. This includes the leaves, flowers and seeds. The top part of the plant is usually the top third. In this method the stems are left standing and depending on which variety is grown, can be harvested separately. The top is cut from the stem with a combine-jaw and then processed in the combine. The combine separates the seed from the rest. It’s also possible to catch the leaves that end up in a tipper through a shredding construction.

Short varieties, such as Finola, can be harvested with most combines with little or no modification. Draper headers are advised for straight combining because they cut and feed the combine uniformly. Hemp is tough and fibrous and stems may wrap on auger headers. When combining hemp, new knives and guards are imperative to avoiding plugging.

Conventional and single rotary combines are preferred. Larger capacity combines with conventional cylinders >1.25 m help deal with the high volume of large fibrous material going through the combine. Dual rotary combines are at risk of fibre wrapping and jamming the opposing rotors and are therefore less desirable. Frequent monitoring for fibre wrapping and clearing hot surfaces, such as the engine, can prevent combine fires. Combine speed should be set to provide uniform crop flow through the combine to prevent plugging and wrapping. A sharp curved knife is useful for cutting away fibre wrapped around the machinery. It is advised to frequently check and clean the threshing unit as build up of plant material here is likely. Additionally, if you intend to harvest more hemp the following day, all equipment should be cleaned to stop trapped contaminated seed mixing with the next day's harvest.

Combine modifications can help to reduce fibre wrapping. Exposed moving parts can be shielded with sheet metal or plastic. Deflectors can be added to keep the crop away from header reel ends and to narrow the feed-house inlet to help keep fibre from wrapping on outer shafts and pulleys. ABS pipe can be placed over front drive shafts to prevent wrapping. Cables and lines should be tied to the machine to help reduce fibre build-up. Header hydraulics can be extended by about 30 cm to raise the header higher for tall varieties.

It should be noted that hemp seed is a thin walled, fragile grain and should be treated carefully to make sure you end up with the highest value product possible at the end. Thus, settings for the combine should be set with this in mind. Settings for the combine can also be altered depending on the moisture content of the plant, however, general settings recommended by HempFlax are as follows:

• Reel speed Approximately 1 km/h faster than the driving speed
• Fan speed 950 rpm
• Threshing cylinder speed 900 rpm
• Top sieve 10 mm
• Bottom sieve 5 mm

Although it’s not current practice, teams have been working to produce a single header for hemp which allows the harvest of both the top and the stem at the same time. This allows for the efficiency of harvesting all the material in one pass. HempFlax and GroeNoord produce a double cut combine which has a lower set of jaws cutting the plant at the base, as well a standard combine-jaw and reel which cuts the top and feeds the top into the combine. For further information and advice on double cut combine harvesting HempFlax should be contacted.

It is important to note that seed can self-heat within 2-4 hours of harvesting and must rapidly be aerated or put through a dryer to preserve seed quality. If harvesting is slow, don’t let hemp seed sit in a trailer at the side of the field for >2 hours before getting to aeration/drying facilities. Ideally hemp seed should be in a grain drier within 1.5 hours of harvesting.

5.2.2. WHOLE PLANT/STEM HARVESTING

If harvesting dual-purpose hemp you will have already cut the tops off your crop and the stems will be standing in the field. Following cutting the tops you can then cut the base of the stems to harvest the stems. The same process is carried out if you intend to harvest the whole plant. Remaining stems can be 0.6-2.4 m tall and whole plants can be over 3 m, hence, a machine able to deal with crops of this height is advisable. The plants are swath or windrow cut at ~20 cm. Standard swathers are generally not able to deal with hemp’s fibrous stems, therefore it’s suggested to use a sickle bar and disc bine. Alternatively a combine that is suitable for hemp can be used. If retting is required, after cutting hemp will remain as swath or windrows for retting and drying. Retting in the microbially driven process where pectins, a binding structure which holds the fibres to the remainder of the flax stem, are broken down releasing the fibres and improving the quality of fibre and making downstream processing easier. Retting can take from 2-6 weeks depending on environmental conditions. Warmer, wetter conditions will reduce the amount of time for retting. This can be advised upon by your hemp fibre processor. The clippings should be turned at least twice during the drying/retting period by using a straw walker. This will separate the crop at a low speed, drying it evenly. The PTO shaft speed should not exceed 350 rpm, this is to avoid spreading the swath too thin and losing heavier material. When turning the swath the driving speed should be 6 km/h. If there is a low volume of biomass it’s not necessary to turn the clippings. Additionally, rowing up swaths can collect up trash and stones, hence, should only be carried out if necessary. Rowing up is usually advised when the yield of biomass is too low for baling. When hemp in the swath reaches 12-15% moisture content it can then be baled for transportation. This can be determined by snapping a stem. If the stem snaps in two rather than just splitting then it is dry enough to be baled.

6. POST HARVEST

6.1. YIELD

Yields will vary depending on the variety grown, what end use the variety is grown for and the environmental factors specific to any one site. Yields of fibre and seed for the different common european varieties are listed in table 1 (section - 2.3 VARIETY SELECTION). It should be noted the data for these yields, albeit averages from 10 years of harvests, are from Central Europe. Average yields for fibre varieties seen in the UK are 7.5 t/ha. If harvesting dual hemp you can expect your fibre yields to fall to 5-6 t/ha with 1 t/ha of seed. On average seed yields will be around 1 t/ha but can reach 2 t/ha if grown in favourable conditions.

Prices for hemp seed and fibre vary. The average price of fibre goes for £160 per tonne in the UK but averages €200 per tonne in Europe are seen. Prices of £500 per tonne of unprocessed seed is standard, however, seed buyers will pay £1500-£1800 per tonne for top quality seed. Additionally, average prices observed for seed in Europe was €1200. It should also be noted that a premium of £300/tonne is usually added for organically grown seed, making the average price for top quality organic seed £1800-£2100.

6.2. DRYING & STORAGE

6.2.1. GRAIN

Depending on the processor, hemp seed must be dried, stored and monitored prior to processing to maintain grain quality. Self-heated, mouldy or contaminated seed will be rejected for food processing. Spoiled hemp seed is worth a quarter of what grain for bird seed goes for and a sixth of what food grade seed goes for. Self-heating, sweating, evaporation and condensation can be high in parts of the grain store/bin/silo leading to pockets of mould or bacterial growth. This can lead to rapid deterioration in grain quality. Prior to seed drying, seed cleaning should be carried out. Contaminant material that makes it through the harvesting process can trigger self heating or mould growth.

Processors usually ask for a specific moisture content of 7-9%, depending on the processor. It’s advised that you contact your processor for specific requirements. Hemp seed may need to be stored for an extended period. Thoroughly cleaned, dried, and closely monitored seed will store for 1-2 years without loss of quality.

Grain drying should be carried out at 45°C with a continuous flow drier, it is imperative that the temperature of the grain itself should not rise to above 35°C. Overheating the seed can lead to discolouration and a degradation in oil composition and seed quality.

When choosing a storage system for hemp, priority should be given to cleanliness, handling, conditioning and aeration capabilities. Silo hoppers with aeration are the best choice. Flat metal silos with aeration flooring are also a good choice. Mini-bulk bags have been used to store hemp as long. This is only applicable if the grain moisture content is below 8% and can be kept below 8% in storage.

6.2.2. FIBRE

Hemp fibre will be pressed into large square bales weighing ~400 kg each. Expedient cutting and baling will minimise fibre wrapping and allow better baling efficiencies. Sisal or hemp twine should be used as poly twine can contaminate the fibre. Plastic net wrapping can be used as it is easily removed. Stalk moisture should be less than 15 per cent at time of baling, and should continue to dry to about 10 per cent in the bale. Once moisture is under 15 per cent no more retting will take place. Round bales may be stored outdoors for a number of years in prairie conditions, but big square bales absorb more rainfall and must be stored under cover to prevent rotting. No observations have been made to date on bales stored under plastic, but experience with hay storage indicates that moisture would be wicked up from the ground and some spoilage would take place unless the bales are separated from the bare ground. This often occurs even on deep gravel floors indoors. Hemp straw also absorbs air moisture quite readily. Larger round balers, solid or hollow core, and large square balers are adequate for baling hemp straw. Large round bales with hard cores may be the best as they are denser and will not pick up moisture during storage. For moving the bales around your site a bale lifter is essential, the bales are usually too dense to be lifted with a bale spike.

6.2.2.1. BALE STORAGE

Baled hemp can be stored in a dry shed for long periods of time. Outdoor storage during the drier seasons is possible, however, if moisture levels begin to increase in the bales, quality can reduce drastically and rapidly. The storage of hemp bales should follow the same rules as the handling and stacking of any bales produced in agriculture. Bales should be stacked safely. Thus, stacks should be sited: Away from public roads and footpaths to reduce the risk of fire from discarded cigarette ends, Away from overhead power lines, Well away from residential properties and where several stacks are sited together, they should be built in a line across the prevailing wind and not less than 24 m apart. All stacks must not be higher than 1.5 times the shortest baseline measurement. Bales should be stacked on the unstrung sides and overlapping bale layers must be included at regular intervals, as well as binding in the vertical columns.

Whilst the stacking and loading of lorries is in progress, we would always suggest that any spectators and people involved should always remain either in their machines or at a safe distance.

6.2.2.2. BALE QUALITY

The best way to retain the quality of your hemp fibre to treat it like any other biomass material i.e. wheat, barley and oilseed rape straw. Square hemp bales take on water quite quickly, this can lead to the degradation of the material and the loss in quality of fibre. To maintain the moisture content at 10% the best method is to keep undercover immediately after harvest. Storage of bales outside can be acceptable practice if it’s managed correctly.

Outside stacks need to be built as high as is possible and then pushed together tightly as the machine and bale quality will allow. A correctly built stack should be safe and result in a minimum amount of product being exposed to the weather. It is very important that outside stacks are sheeted to prevent the top and possibly the second layer being spoilt, leading to material degradation. The consequences of bad storage are damp or starting to rot bales due to being exposed to periods of wet weather. Such bales will inevitably not be suitable for their destined market. This must be considered by you when loading your material for collection.

In the examples above, each layer is stacked in packs of four, three or two; pack size will depend on your machine and operator confidence. The pack size of the top layer will be driven by the reach of your machine and attachment type. The width of the stack should be driven by site, yield and available sheet sizes. Ideally try and build stacks as high and as square as possible to ensure minimum losses. Leaving your baled material in small stacks in the field where harvested will lead to a potentially higher number of losses.

It is important that packs are interlinked as demonstrated above and pushed tightly together to ensure maximum stability. It may be necessary to nudge the stack from behind in the early stages of construction to prevent any bales falling from the rear of the stack.

6.2.2.3. STACK SITE SELECTION

Where is the best place for me to locate my stack of bales?

• Security to satisfy insurance requirements
• Accessibility for lorries
• Distance from power lines
• Free draining ground or ideally a concrete or hardcore pad
• Good level site
• Free from holes, ditches, and other obstacles.

6.2.2.4. BALE DENSITY

Growers should ensure that the bales produced by your chosen contractor are baled to the correct density and shape. When baling is in progress it is important to physically check your bales at the start of the operation and monitor them at intervals throughout the day. Good, tight bales should feel hard when kicked and it should prove difficult to get your hands under the strings and lift the string to any distance. It should not be possible to pull the strings off a bale by hand!

Some of the problems of not having your product baled correctly:

• More broken bales when clearing fields, loading trailers and trucks etc.
• Excessive bale damage from handling equipment
• Un-storable in outside stacks, due to being on open bale
• Hard to achieve a tidy stack and build to a sufficient height
• Excessive use of indoor storage space
• Impossible to achieve maximum weight onto the Lorries resulting in increased haulage costs per tonne of material
• Possible rejection at process site.
• Increased baling cost to you the producer (because of more bales)

6.2.2.5. BALE SIZE

6 string bales are preferred to 4 string bales which are generally not wanted as they do not lend well to haulage and handling systems. (e.g. Mini Hesston, MF182, Claas 2100). Bales should be produced 2.5 m (8ft) in length so as to ensure maximum weight per bale and value for money from the service supplied to you.

6.2.2.6. BALE HANDLING

Having the correct handling attachment on your telescopic handler or loader will ensure ease of operation and enable efficient loading for the haulage company. Haulage companies will generally prefer the bales to be loaded lengthways along the vehicle bed. For this to be achieved when loading the vehicle, at least a two-pronged spike should be used, which can handle at least a couple of bales at a time. The more favourable alternative to this is possible, would be a multi bale grab. This type of loading grab is generally safer and considerably quicker to use. Lorries ideally need to be loaded within 45 minutes.

6.3. TRANSPORTATION

6.3.1. GRAIN

Conventional transportation equipment used for cereal grains or oilseeds is sufficient. Oval shaped seeds range from about 2.5-3.5 mm. There can be significant variability in grain size among very diverse grain and fibre varieties. There, it is best to understand the seed size before transportation. This information can be measured yourself, or obtained from your planting seed supplier.

6.3.2. BALE

Transportation of bales will be subject to restrictions on load dimensions and weight. Weights should not exceed a reasonable weight, having regard to the engine capacity, brakes, tyres, and general construction of the vehicle.

6.3.3. DIMENSIONAL LIMITS

Dimensional limits that apply to agricultural vehicles in the UK as of January 1, 2016: Length = 12 m (or 18.75 m when combined – i.e. tractor and trailer or other interchangeable towed equipment). Height = 4.65 m. Trailers used to transport loads of baled agricultural produce such as hay or straw etc. are exempt from this height limitation. Widths =

• Agricultural tractors and trailers – 2.55 m;
• Large tractors – tractors with a laden weight exceeding 7.52 tonnes – 2.75 m;
• Tractors with flotation tyres or dual wheel systems – 3.5 m; and
• Fully mounted equipment and interchangeable towed equipment – 3.0 m.

The limit will allow ~31 large Heston square bales. If you are operating a stepped frame floor you will lose 2 bales on the floor, and you can only achieve 9 bales on the floor as opposed to 11 bales on a flat trailer and 11 bales on rows 2 and 3. Most trailers will only take 2 rows of large square bales height, but the step frame will go 32 bales in height allowing 31 bales in total. The 8x4x4 bales tend to be around 400 kg in weight. If they are baled fresh, bales will be heavier and shed stored bales will be lighter. The total tonnage is therefore 15.5 tonnes per load in large bale form.

6.4. SITE RESTORATION

Hemp is an annual crop, thus dies off at the end of the season, however, hemp stubble will remain in the field. Hemp stubble in the ground can cause issues with seeding the following season. The best approach to avoid issues with seeding the following growing season is to use a double disc harrow with notched edge discs to break up the remaining stubble into the ground. This allows the remaining nutrients in the stem and root neck/collar to be returned to the soil for the following crop. It is advisable to rotate to another crop after growing hemp, however, if reseeding with hemp then the same protocol is followed as aforementioned in this document.

7. ADVANTAGES & DISADVANTAGES

7.1. ADVANTAGES

• Environmentally friendly: hemp is a relatively sustainable crop that requires less water and pesticides than most crops.
• Versatility: hemp is a versatile crop. It can be attributed to a variety of end uses, including textiles, biocomposites, paper, food, oils and even fuel.
• Growing market: the global market for hemp is currently growing. Hence, potential for farmers to make a profit from growing hemp.
• Job creation: because of the growing market for hemp jobs will become available in the hemp sector, whether it be on the farming side or within the processing of hemp.

7.2. DISADVANTAGES

• Regulatory issues: although legal in the UK there are regulatory issues around the amount of THC that is allowed in the crop. Hence, the crop requires a licence to grow. However, licensing is a fairly simple process and we believe it will become easier in the future.
• Lack of infrastructure: because of hemp's exclusion from agriculture over the last 60 years there is currently a lack of infrastructure for processing and manufacturing hemp.
• Limited market: there is a limited market for hemp when compared to other crops. However, due to its environmental benefits, versatility, and growing global market there will be more demand for the crop in the years to come.

8. LEGISLATION

The cultivation of hemp is legal in the UK, but it is subject to strict regulations. The legislation surrounding the cultivation of hemp in the UK is mainly governed by the Misuse of Drugs Act 1971 and the Misuse of Drugs Regulations 2001.

Under UK law, hemp is defined as cannabis that contains <0.2% THC, which is the psychoactive component of cannabis. This means that farmers are only permitted to grow hemp strains that have been certified as having a THC content of less than 0.2%.

In order to grow hemp legally in the UK, growers must first go through the authorised criminal record check process. Then, growers must obtain a licence from the Home Office, or the Department of Health in Northern Ireland. The licence application process involves providing detailed information about the proposed cultivation site, the varieties of hemp to be grown, and the intended use of the crop, and outlining how the destruction of plant matter deemed illegal for harvest is carried out.

Once a licence has been granted, farmers must comply with a range of regulations, such as keeping detailed records of the cultivation and harvesting process and ensuring that their crops do not exceed the legal limit for THC content.

It is also worth noting that while hemp cultivation is legal in the UK, the use of hemp for medicinal purposes is strictly regulated and requires a separate licence from the Medicines and Healthcare products Regulatory Agency (MHRA).

https://www.gov.uk/guidance/controlled-drugs-industrial-hemp