A Seed Saved: How to Harvest & Store Plant Seeds
Preserving seeds successfully requires some trial and error, but the process can be fun and rewarding. Growing plants from seed is a nice way to re-create a gardening success, share your carefully cultivated good fortune with others or just save some money. Seeds may look tough and self-contained, but they’re designed to react to the environment around them. Here’s a few things to keep in mind when handling seeds that haven’t made it into the ground yet.
Planting a seed where you—not nature—decides is a powerful activity. Vast cities have sprouted near-rich farmlands, and whole cultures have revolved around the dynamic contributions of specific plants to human life and culture. All of that would have been much more difficult, if not impossible, without the ability to harness the vitality and mystery of the humble seed.
This Isn’t Your Grandma’s Seed Stock
Saving seeds at home used to be a much more common activity than it is today. During the first half of the 20th century, it wasn’t unusual for families to maintain backyard gardens containing heirloom, open-pollinated plant varieties. In fact, in 1943, at the height of the Second World War, an estimated 40% of produce consumed was grown in victory gardens located primarily on private lands. Seeds for those vegetable gardens were probably sourced locally and later harvested from those backyard gardens.
Although times have changed, growing produce and other plants at home has seen a resurgence during the last decade or so. Is preserving seeds a simple process? Sure, it can be. But there are more factors to consider than there were 70 years ago. Scientists have been hard at work tinkering with plant genetics, which means there are lots of hybrid plants available that may look and taste great but not reproduce true to the original plant. Part of the art of saving seeds is recognizing which ones are good candidates for preservation, and which aren’t.
Natural Selection Isn’t Just About the Birds and the Bees
Preserving seeds from your best plants is a good way to cultivate strains that are well-adapted to your specific growing conditions, indoors and out. It’s natural selection, with a little friendly encouragement. You don’t need to be a geneticist to do it, either. The seeds you choose to preserve and plant later are probably from the hardiest plant specimens. When you save those plant seeds, you preserve the very traits new plants need to survive in your landscape, greenhouse or grow tent.
A Seed-Saving Primer
The conditions you need for good seed germination (warmth and moisture) are the opposite of what you need for good seed preservation. Seeds may look tough and self-contained, but they’re designed to react to the environment around them. When you remove enough moisture and keep them chilled, they stay dormant, waiting for conditions to improve. Some experts believe a seed that’s kept dry enough and at a consistently cool temperature can last a decade or sometimes much longer. For the home grower it can vary, but a good general rule is high-quality seeds should last two to three years if stored carefully. Larger seeds will typically remain viable somewhat longer than smaller seeds. Here are some important steps for saving seeds for future use, trade or sale.
Avoid hybrid seeds – With hybrid seeds, what you see isn’t necessarily what you get. Hybridization is a complex process in which two separate-but-stable plant strains are cross-pollinated to produce a third plant variety that hopefully exhibits the best characteristics of both parent plants. This second generation plant is typically referred to as an F1 hybrid. When it matures and sets seed, the seedlings may be more like one of the grandparent plants, or could exhibit completely unexpected and unwelcome characteristics. If you’re a gambler, go ahead and give hybrids a try. If not, check the labeling on the plants you purchase to make sure they are heirloom stock or open-pollinated cultivars.
Choose open-pollinating plants for seed stock – The term open-pollinated can be somewhat deceptive. It sounds like a random process that can lead to more chaos and potentially bad seedlings than a hybrid cross. It turns out nature is pretty clever, though. Open-pollinated plants, or plants that have developed in nature over time without human intervention, produce reliably consistent results. Generation after generation, these seeds will produce plants similar to the parent plant. This makes them excellent candidates for future cultivation. The one exception is when an open-pollinated plant cross-pollinates with a closely related plant. This can sometimes occur when plants from the same genus and species are grown in close proximity to one another. To avoid surprises, grow only one genus and species variety at a time unless you can keep similar specimens completely separate. A plant’s Latin name will provide important clues about its likelihood of crossing with other plants in your collection.
Choose seed plant specimens carefully – Small variations may make their way into future generations of even non-hybrid plants. If you’re collecting seeds instead of cloning plants, a little variability is inevitable. The trick is to hedge your bets by selecting plants for seed that represent your wish list for future generations. This can include things like hardiness, flavor, flower color, size and so on. Most experts agree it’s better to settle for fewer seeds overall than to harvest seeds from inferior plants. When you’ve made your plant selections, allow those specimens to dedicate their energies to setting seed. Once a plant goes into seed production mode, it has little energy left over for other types of activity, like producing additional leaves or flowers. Recognizing which plants you want for seed early in the growth process is one key to a good seed harvest.
Don’t harvest seed too soon – When it comes to harvesting seeds, timing is important. As gardeners, we’re used to harvesting plant products when they’re flavorful or at their most attractive. Flowers, fruits and vegetables typically produce mature seeds late in the growth process, though, usually after the flowers have withered, the pods have dried completely or the fruits have become overripe. When in doubt, wait. An immature seed will never sprout, so give seed stock plenty of time to mature.
Is that a seed, a bit of fluff or a twig? – It would be nice if all plant seeds looked more or less identical, but it doesn’t work that way. Seeds can look like dried petals, twigs, fluff, dead worms or other unremarkable things, or they can be so small they are difficult to see. Before you grab your harvesting kit, familiarize yourself with the appearance of the seeds you’re after so you won’t be disappointed later.
Dry seed processing – Although there are many plant varieties, most seeds are harvested using either a dry or wet processing method. Dry processing is about what you’d expect: allow seed heads to dry completely, preferably on the plant. Transfer seeds to a screen or other surface where they can be separated from extraneous plant material. If seeds can’t be dried completely on the plant, they can be transferred to a paper bag, or flowering heads can be suspended by their stems in a warm, dark location for additional drying.
Wet seed processing – Wet seed processing is used to prepare seeds from fleshy fruits like melons. Some quasi vegetables are handled in this way as well, including cucumbers and tomatoes. Fermentation is part of the process, which means the seeds aren’t dried on the plant. Instead, they’re removed from the fruit along with some of the pulp and allowed to mellow through the actions of naturally occurring yeasts. This typically takes a few days. Here’s how it works: A slurry of seeds, pulp and water is allowed to ferment in a cup, bucket or other wide-mouth container that is shaken or stirred regularly. Viable seeds eventually sink to the bottom of the container, while the pulp and non-viable seeds float to the top where they can be skimmed off. After five days or so, the seeds are removed and dried on a screen or paper plate, in a mesh bag or on another neutral surface. Different seed experts have their own methods for processing wet seeds, but they typically follow this similar pattern.
Seed cleaning – After drying, be sure to remove any debris from seeds before storing them. The presence of extra stuff can encourage mold or bacterial growth. Some veteran seed collectors recommend freezing prepped seeds for up to three days to kill any incipient bacteria or mold they may be harboring. A clean seed is a safe seed. Removing good seed stock from the surrounding chaff can be tiresome, but threshing and winnowing are both time-honored methods for removing large and small bits of debris from seeds. For the casual gardener, placing dried seeds on an old window screen and gently shaking the screen can help separate stem pieces, bits of leaves and partial seed casings. Employing a small, hand-held fan can also help.
Controlling temperature and humidity – The two most important factors when storing seeds are temperature and humidity. The temperature part of the equation can be pretty simple. Keep seeds in a refrigerator if you can. Other good choices are in a dry basement or root cellar. The humidity part can be tricky. For the pros, the optimal humidity for seed storage may be less than 8%. For the home grower using conventional drying methods, it probably hovers around 25% or so.
Low humidity is achieved by choosing seed containers that seal well, paired with desiccants like silica gel that absorb ambient moisture. Seed savers have been using do-it-yourself moisture absorbers for a long time, including powdered milk, dried rice and non-clumping kitty litter. Just keep a layer of cotton or paper towel between the desiccant and the seeds.
Purists often prefer air-tight glass or plastic containers for seed storage. Where space is a problem, some green thumbs like using small envelopes stored inside larger sealable bags. Some popular options include coin envelopes, small parts envelopes, styrene or glass vials with snap-on caps (available for purchase in bulk), sterilized baby food jars and used (and thoroughly cleaned) prescription bottles.
Labeling – Keeping track of seeds can be a nightmare if you don’t maintain good records. Starting a gardening log is a good idea, but even if you aren’t into taking notes, be sure to label your seed stores carefully. The experts recommend including the plant’s Latin and common names, the date the seeds were collected and any special information you may think you’ll need later. This can include the source of the original plant or starter seeds you used, and what you want to achieve with your next crop.
Preserving seeds successfully requires some trial and error, but the process can be fun and rewarding. Growing your own seed is a nice way to re-create a gardening success, share your carefully cultivated good fortune with others or just save money the next time around. So, save your seeds. It’s the smart thing to do!
Cannabis sativa L.
Source: James A. Duke. 1983. Handbook of Energy Crops. unpublished.
A multiple-use plant, furnishing fiber, oil, medicine, and narcotics. Fibers are best produced from male plants. In the temperate zone, oil is produced from females which have been left to stand after the fiber-producing males have been harvested. Leaves are added to soups in southeast Asia. Varnish is made from the pressed seeds. Three types of narcotics are produced: hashish (bhang), the dried leaves and flowers of male and female shoots; ganja, dried unfertilized inflorescences of special female plants; and charas, the crude resin, which is probably the strongest. Modern medicine uses cannabis in glaucoma and alleviating the pains of cancer and chemotherapy. More resin is produced in tropical than in temperate climates. Lewis lung adenocarcinonoma growth has been retarded by oral administration of delta-9-tetrahydrocannabinol, delta-8-tetrahydrocannabinol and cannabinol, but not by cannabidiol. (J.N.C.I. 55: 597-602. 1975). The delta-9 also inhibits the replication of Herpes simplex virus.
Medicinally, plants are tonic, intoxicant, stomachic, antispasmodic, analgesic, narcotic, sedative and anodyne. Seeds and leaves are used to treat old cancer and scirrhous tumors. The seed, either as a paste or as an unguent, is said to be a folk remedy for tumors and cancerous ulcers. The decoction of the root is said help remedy hard tumors and knots in the joints. The leaf, prepared in various manners, is said to alleviate cancerous sores, scirrhous tumors, cold tumors, and white tumors. The plant is also used for mammary tumors and corns (C.S.I.R., 1948-1976). Europeans are said to use the dregs from Cannabis pipes in “cancer cures” (Watt and Breyer-Brandwijk, 1962). Few plants have a greater array of folk medicine uses: alcohol withdrawal, anthrax, asthma, blood poisoning, bronchitis, burns, catarrh, childbirth, convulsions, coughs, cystitis, delirium, depression, diarrhea, dysentery, dysmenorrhea, epilepsy, fever, gonorrhea, gout, inflammation, insomnia, jaundice, lockjaw, malaria, mania, mennorhagia, migraine, morphine withdrawal, neuralgia, palsy, rheumatism, scalds, snakebite, swellings, tetany, toothache, uteral prolapse, and whooping cough. Seeds ground and mixed with porridge given to weaning children.
Most varieties contain cannabinol and cannabinin; Egyptian variety contains cannabidine, cannabol and cannabinol, their biological activity being due to the alcohols and phenolic compounds. Resin contains crystalline compound cannin. Alcoholic extracts of American variety vary considerably in physiological activity. Per 100 g, the seed is reported to contain 8.8 g H2O, 21.5 g protein, 30.4 g fat, 34.7 g total carbohydrate, 18.8 g fiber, and 4.6 g ash. In Asia, per 100 g, the seed is reported to contain 421 calories, 13.6 g H2O, 27.1 g protein, 25.6 g fat, 27.6 g total carbohydrate, 20.3 g fiber, 6.1 g ash, 120 mg Ca, 970 mg P, 12.0 mg Fe, 5 mg beta-carotene equivalent, 0.32 mg thiamine, 0.17 mg riboflavin, and 2.1 mg niacin. A crystalline globulin has been isolated from defatted meal. It contains 3.8% glycocol, 3.6 alanine, 20.9 valine and leucine, 2.4 phenylalanine, 2.1 tyrosine, 0.3 serine, 0.2 cystine, 4.1 proline, 2.0 oxyproline, 4.5 aspartic acid, 18.7 glutamic acid, 14.4 tryptophane and arginine, 1.7 lysine, and 2.4% histidine. Oil from the seeds contains 15% oleic, 70% linoleic, and 15% linolenic and isolinolenic acids. The seed cake contains 10.8% water, 10.2% fat, 30.8% protein, 40.6% N-free extract, and 7.7% ash (20.3% K2O; 0.8% Na2O; 23.6% CaO, 5.7% MgO, 1.0% Fe2O3, 36.5% P2O5, 0.2% SO3; 11.9% SiO2, 0.1% Cl and a trace of Mn2O3). Trigonelline occurs in the seed. Cannabis also contains choline, eugenol, guaiacol, nicotine, and piperidine (C.S.I.R., 1948-1976), all listed as toxins by the National Institute of Occupational Safety and Health. A beta-resercyclic acid derivative has antibiotic and sedative properties; with a murine LD56 of 500 mg/kg, it has some aritiviral effect and inhibits the growth of mouse mammary tumor in egg embryo (Watt and Breyer-Brandwijk, 1962).
Non-users may suffer muscular incoordination (9 of 22 persons), dizziness (8), difficulty concentrating (8), confusion (7), difficulty walking (7), dysarthria (7), dry mouth (7), dysphagia (5), blurred vision (5), and vomiting (1), following oral ingestion of THC disguised in cookies (MMWR, October 20, 1978). People working with the plant or the fiber may develop dermatitis. In larger doses, hemp drugs may induce catalepsy, followed by coma and DEATH from cardiac failure (C.S.I.R., 1948-1976).
Annual herb, usually erect; stems variable, up to 5 m tall, with resinous pubescence, angular, sometimes hollow, especially above the first pairs of true leaves; basal leaves opposite, the upper leaves alternate, stipulate, long petiolate, palmate, with 3-11, rarely single, lanceolate, serrate, acuminate leaflets up to 10 cm long, 1.5 cm broad; flowers monoecious or dioecious, the male in axillary and terminal panicles, apetalous, with 5 yellowish petals and 5 poricidal stamens; the female flowers germinate in the axils and terminally, with one 1-ovulate ovary; fruit a brown, shining achene, variously marked or plain, tightly embracing the seed with its fleshy endosperm and curved embryo. Fl. summer; fr. late summer to early fall; year round in tropics. Seeds weigh 1.5-2.5 gm/100 seeds.
As Cannabis sativa has been cultivated for over 4,500 years for different purposes, many varieties and cultivars have been selected for specific purposes, as fiber, oil or narcotics. Drug-producing selections grow better and produce more drug in the tropics; oil and fiber producing plants thrive better in the temperate and subtropical areas. Many of the cultivars and varieties have been named as to the locality where it is grown mainly. However, all so called varieties freely interbreed and produce various combinations of the characters. The form of the plant and the yield of fiber from it vary according to climate and particular variety. Varieties cultivated particularly for their fibers have long stalks, branch very little, and yield only small quantities of seed. Varieties which are grown for the oil from their seed are short in height, mature early and produce large quantities of seed. Varieties grown for the drugs are short, much-branched with smaller dark-green leaves. Between these three main types of plants are numerous varieties which differ from the main one in height, extent of branching and other characteristics. Reported from the Central Asia, Hindustani, and Eurosiberian Centers of Diversity, marijuana or cvs thereof is reported to tolerate disease, drought, fungus, high pH, insects, laterite, low pH, mycobacteria, poor soil, slope, and weeds. (2n = 20, 10, 40.)
Native to Central Asia, and long cultivated in Asia, Europe, and China. Now a widespread tropical, temperate and subarctic cultivar and waif. The oldest use of hemp seems to be for fiber, and later the seeds began to be used for culinary purposes. Plants yielding the drug seem to have been discovered in India, cultivated for medicinal purposes as early as 900 BC. In medieval times it was brought to North Africa where today it is cultivated exclusively for hashish or kif.
Plants very adaptable to soil and climatic conditions. Hemp for fiber requires a mild temperate climate with at least 67 cm annual rainfall, with abundant rain while seeds are germinating and until young plants become established. Thrives on rich, fertile, neutral to slightly alkaline, well-drained silt or clay loams with moisture retentive subsoils; does not grow well on acid, sandy soils. Of the many types of hemp, some are adapted to most vegetated terrains and climates. Ranging from Cool Temperate Steppe to Wet through Tropical Very Dry to Wet Forest Life Zones, marijuana is reported to tolerate annual precipitation of 3 to 40 dm (mean of 44 cases = 9.9 dm), annual temperature of 6 to 27°C (mean of 44 cases = 14.4), and pH of 4.5 to 8.2 (mean of 38 cases 6.5) (Duke, 1978, 1979).
Propagation mainly by seed. Experimentally, drug plants have been propagated from cuttings but such plants do not come true as to drug content of parent. Seeds stored in cool, dry place remain viable for up to two years. Hemp seed sown as early in spring as possible. Before sowing, land is plowed (in fall) several times to a depth of about 20-23 cm and repeatedly harrowed the land. In spring the land is harrowed again and rolled, making a firm tilth over the entire surface. In some areas a first plowing is done in the fall and red clover or lupin planted; in January or February a second plowing turns these under as a green-manure. Generally sown in March, seeds germinate at low temperature, but not below 1deg.C. Rate of seed sown varies with type of fiber desired; for coarse fiber for cordage and coarser textiles, 2.5 bu/ha is used; for finest fibers, 7.5-10 bu/ha used. Seed sown by machine in rows from 12 cm upwards, placing the seed at depth of 3.5 cm at rate of 40-60 kg/ha. In many countries seed sown broadcast. When grown for seed (oil), seed sown by drills; then such plants sometimes reach height of 5.3 m with thick stems up to 5 cm in diameter, much-branched. For fiber, stems up to 2 m tall and 0.5 cm in diameter are best; larger stems tend to get woody and have lower fiber content. Besides, they are more difficult to handle during harvesting, retting and scutching. Plants require little cultivation, except for weeding during early stages of growth. Hemp grows rapidly and soon crowds out weeds. After plants are 20 cm tall, weeding is abandoned. Hemp tends to exhaust the soil of nutrients. Some nutrients are returned to the soil after plants are harvested. On medium fertile soils a dressing of farm manure or a green-manure crop should be added and turned under. Chalk, potash, or gypsum may be applied to the soil to add the needed nutrition. Sodium nitrate and ammonium along with potassium sulfate have a beneficial effect on the fiber crop. Fiber-producing plants should always have plenty of proper nutrients, especially nitrogen, which is the most important element needed. Irrigation is seldom practiced.
Hemp is ready for harvest four to five months after planting, rarely earlier for some varieties. Harvesting depends on the climatic conditions, the variety of hemp grown and whether the crop is being grown for hemp or seed. In temperate areas, hemp is usually harvested from mid July to mid August. Both male and female plants look alike until they flower; then the male plants turn yellow and die, whereas the female plants remain dark green for another month until the seed ripens. Male plants are ready to harvest for fiber when the leaves change from dark green to light brown. The best yield of fiber (and only male plants are used) is then obtained. Hemp is harvested when the staminate flowers are beginning to open and shed their pollen. Seed is harvested from the female plants when most of it falls off when the plant is shaken. Best time of day to harvest seed is in early morning when fruits are turgid and conditions damp. As fruits dry out by mid-day, seed loss increases due to shattering. Usually stems are cut and the seeds shaken out over canvas sheets or beaten with sticks to extract the seeds. For fiber, hemp plants are cut by hand with a hemp knife, similar to a long-handled sickle. Plants are cut 2-3 cm above the ground and spread on the ground to dry. In some areas, the entire plants are pulled up and laid out to dry. Hand cutting, one man can cut about one-fifth hectare per day. Sometimes specially designed harvesters with a tractor are able to harvest four hectares a day. In many areas several varieties of hemp are grown so as to spread out the harvest, one maturing in late July and used later for seed crop in September, a second crop maturing in mid August, and a third maturing near end of August. Fiber is extracted from the stems of hemp by retting by methods similar to those used for other fiber plants. Sometimes the stems are dried before they are retted. After plants have air-dried for 4-6 days, the root and flower ends are cut off and the remaining portions, with branches and leaves taken or beaten off, are made into small bundles. For retting, 15-20 of these smaller bundles are made into larger bundles. In other areas stalks are not dried before retting, green stems, after roots and flower ends have been cut off, are made into bundles, and retted immediately. Hemp can be water retted, dew retted, or snow retted, according to the climatic conditions. The retted hemp stalks consist of fiber in the outer rind and a woody interior portion. Fiber is separated from the stalk by a breaking process. Stalks are dried after retting and the woody shive is broken into short pieces called hurds. Eventually the fibers are separated from the interior woody pieces by scutching by passing the bundles through a number of fluted rollers and then past large revolving drums with projecting bars which remove any remaining pieces of wood. Machines are able to handle 3-3.5 MT dried straw every hour, producing 0.4-0.5 MT of cleaned fiber.
Yields and Economics
Yields of hemp per hectare depend on climatic conditions, variety grown, soil and nutrition, and spacing of plants in the field. Weight of dried stems per hectare is usually between 4.5 to 7.5 T, with a yield of fiber about 25% of the dried stalks. Usually the taller the plant, the longer will be the fiber with a greater yield per plant. In some areas fiber yields of 850- 1,700 kg/ha compared to 1,300-1,700 kg/ha seed and 30 kg ganja. The U.S.S.R. is the largest producer of hemp in the world, producing about 33% of hemp fiber, annually 105,000 MT compared to the world production of 255,000 MT (excepting China). France and West Germany are the chief importers, Italy and Yugoslavia exporters. Chile, China, Japan and Peru also produce hemp. Narcotic production is usually clandestine, but there is legal marijuana production in India. India is the main producer and exporter of oil from the seed.
In India, plants remaining in the field after harvesting for fiber are allowed to set seed. They are cut after the fruits are ripened and dried and threshed for seed collection. Grown solely for seeds, an average crop yields 1.3 to 1.6 MT/ha seed. The world low production yield was 288 kg/ha in Democratic People’s Republic of Korea, the international production yield was 613 kg/ha, and the world high production yield was 3,842 kg/ha in People’s Republic of China.
Among diseases of Cannibis are: Botryosphaeria marconii (stem canker, wilt), Botrytis cinerea (gray mold), Cylindrosporium sp. (leaf spot), Fusarium sp. (canker, stem rot), Gibberella saubinetii (stem rot), Hypomyces cancri (?root rot), Macrophominia phaseoli, Phomopsis cannabina, Phymatotrichum omivorum (root rot), Sclerotinia sclerotiorum (stem rot, wilt), Sclerotium rolfsii (southern blight), Septoria cannabis (leaf spot). Nematodes include: Ditylenchus dipsaci, Heterodera humuli, Longidorus maximus, Meloidogyne hapla, M. incognita, M. incognita acrita, M. spp., and Pratylenchus coffeae (Golden, p.c., 1984). Occasionally Orobanche ramosa is paratitic on the roots.
Hemp Production for Fiber or Grain – Revised
Figure 1. Ismail Dweikat, University of Nebraska-Lincoln professor of agronomy and horticulture, stands amid research plantings of 6-7 foot tall hemp plants, these varieties best suited to fiber and grain production.
Hemp Production for Fiber or Grain – Revised
University of Nebraska-Lincoln Extension information is typically based on the interpretation of research information from Nebraska or elsewhere in the Midwest. However, such information is not available for hemp production due to previous restrictions on research in the U.S. This publication relies heavily on research findings from Europe and Canada. See more stories in this series at https://cropwatch.unl.edu/tags/hemp.
In Nebraska, hemp grown for fiber or grain will more closely match existing cropping systems than hemp grown for CBD. Fiber/grain hemp could increase diversity for current rotations, but may offer some challenges, given no pesticides are currently labeled for pest management. Hemp production for fiber and/or grain can be highly mechanized with labor demands per acre similar to that of other agronomic crops, except for weed control and harvest operations which require relatively more time for hemp.
Seed sources and varieties
Grain production may be optimized with no more than 150,000 plants per acre and sowing 20 to 30 lb/ac of seed. Fiber production may be best when planting in row spacings of less than 12 inches, however, some do plant in 30’ rows. The seed rate maybe 25 to 30 lb /ac. High plant density results in tall plants capable of producing longer fibers. Hemp can be sown with a grain drill such as used for wheat. The seed weight has been estimated at 15,000 to 27,000 seed per pound (1000 kernel weight of 18-22 grams; the seed will be smaller for monoecious varieties). The seed is fragile and can be damaged during planting. With air planters, the fan speed should be set at low.
In Europe, fiber yields were not increased by having more than 182,000 plants per acre and this plant density resulted in better quality fiber than with higher plant densities. Hemp plant stands are likely to self-thin as more vigorous plants suppress the less vigorous, such as the male plants. Seed placement should be ½ to ¾ inch deep; some recommend seeding at more than a 1-inch depth in dry soil.
Soil temperature should be about 55 o F. Emergence is likely three to five days after spring planting. Hemp is more tolerant of low soil temperature at planting than corn and while seedlings can be killed by an early frost, hemp survived a 24 o F temperature in May in Canada.
Fertilizer recommendations have not been determined for Nebraska. Penn State University has recommended 150 lb/ac N, 30 lb/ac P2O5 and 20 lb/ac K2O. In a series of trials in Europe, mean fiber yield did not increase with when nitrogen was increased from 90 lb/ac to 140 lb/ac; however, in another set of trials conducted in the Netherlands, fiber yield increase as the N rate was increased to 180 lb/ac. In Alberta Canada, grain yield peaked with 110 lb/ac N and fiber yield peaked with 80 lb/ac N. The optimal P and K rates will depend on soil test values.
Weed, Disease, and Insect Management
A list of products allowed for pest control is provided by the Nebraska Department of Agriculture. Weed suppression with narrow rows, high plant density, and tall plants is important for fiber production. If planted in 30” rows, inter-row cultivation may be needed for early weed control. Hemp can be planted no-till following a burn-down application of herbicide.
There is potential for disease and insect pest problems but information and recommendations are lacking for Nebraska and other states. No pesticides are labeled for hemp in the US. Therefore, rotation of hemp with other crops may an important component of integrated insect and disease management for hemp production. Hemp may benefit other crops in rotation such as through suppression of weeds and some nematode species by hemp. In Alberta, gray mold has been a problem and rotation with canola was found to increase sclerotinia.
As with any grain crop, the proper harvesting, processing, transportation, and storage are critical to prevent spoilage and ensure the highest value for the harvested grain. Hemp grain is thin-walled and fragile, requiring care in harvest, storage, and transport. A grain drying facility is needed and grain drying should begin within 1.5 hour of harvest. Drying can be at 140 o F with a continuous flow drier but grain temperature should not exceed 100 o F to avoid ‘toasting’. Hemp grain, about the size of sorghum grain, contains 29-34% oil of which 15-25% is alpha-linolenic acid (an omega 3 fatty acid) compared with 35-45% oil content for flax of which 70% may be alpha-linolenic acid.
Hemp is swath or windrow cut for fiber production at about 8” between early bloom and seed set when the lower leaves of female plants begin to yellow. The windrows are baled at 12% moisture content and the bales are transported for processing to remove and separate the bast and hurd fibers. Bast fiber concentration is highest in the “bark” of the stem while high lignin but shorter hurd fibers dominate in the rest of the stem. Therefore, wider diameter stems are preferred. Common fiber yields are 15-22% of stem dry weight. A multi-cut combine is available that harvests the upper plant for grain while windrowing the stems; it seems it works well for some varieties but not all. An alternative for harvesting both grain and fiber is to harvest these in separate passes, maybe giving the stems more time to dry before cutting for the fiber harvest.
Information is scarce. We have not learned of any large-scale commercial heap decortication facility operational in US. Small-scale hand-fed equipment is marketed on-line. Canadian Greenfield Technologies has their patient pending HempTrain™ which is described as capable of handling baled hemp feedstock and separation of the high-CBD fraction, green microfiber, bast fiber, hurd, and grain fractions. It is reported to be capable of processing feedstock at 1 t/hr.
Traditionally, hemp was left in the field for up to five weeks after cutting for retting (dew retting), a decomposition process that breaks the bonds between the outer long bast fibers and the inner shorter hurd fibers. However, dew retting is subject to weather conditions and uncontrolled with inconsistent and often negative effects on fiber quality. An alternative to dew retting is water retting which requires much clean water which should be treated before discharge. More common may be mechanical fiber separation without any retting or maybe with an enzymatic treatment.
It appears the 2019 supply greatly exceeded demand and hemp fiber and grain feedstock prices plunged during 2019. The supply/demand discrepancy was greater for the Great Plains compared with some other areas. Rather than outright purchase of feedstock at an agreed price, processors offered growers a profit share arrangement on the product once sold. Available market information is too weak for prediction but indicates a need for caution. Some brokers and processors may be new with little capacity to fulfill obligations under adverse conditions with risks of failed contracts or delayed acceptance of feedstock. See a USDA ERS Feb 2020 report.
Hemp Production Budgets
For information on budgeting for hemp grain, fiber and CBD production, see worksheets from Pennsylvania State University and from the University of Kentucky.