For grain production, desired final plant population is around 100-150 plants/m2. Like fibre hemp, seeds are still planted in 15-18 cm (6-7 in.) rows. Soil temperature determines the optimum planting date. This date may range from late April in Kent and Essex counties to late May in Northern Ontario. Do not plant after the first week of June. Observations in Northern Ontario indicate that grain yield may not respond as positively to early planting as does fibre yield, but early planting may help to advance the harvest date.
Tamm determined that hempseed needs a minimum temperature of 1-2o C for germination and emergence. It should not be sown until the soil temperature rises to 10o C. The optimum temperature is 35o C; the maximum is 45o C, at which temperature the seeds sprout within 12 days. Young hemp plants can survive frost as low as -5o C, but the plants will stop growing even if warm weather follows. The temperature range for hemp growth is 19-25o C (66-77o F). Hemp enters into its rapid growth stage (about 2 inches/day) when the average temperature rises to 16o C (61o F). If southern varieties of hemp are grown in northern latitudes, however, the fiber might not attain technical maturity within 110-115 days, and certainly their seeds will not ripen. The farmer must consider this when selecting a hemp cultivar for his location.
FROM A VERY GOOD STUDY: http://www.rexresearch.com/hhusb/hh2cul.htm
Production is estimated using information on yield and acres harvested. Industrial hemp yield
(grain or fibre) varies with variety, plant population, soil conditions, timing of harvest, and annual
climatic conditions. The highest seed yield recorded to date in Canada has topped 2,000 lbs per acre; an average yield is between 600 to 800 lbs per acre, but rising (Canadian Hemp Trade Alliance). An acre will also produce an average of 5,300 lbs of straw, which can be transformed into about 1,300 lbs of fibre.
There is a Hungarian expert. He states: We called this cultivar “UNIKO-B”. It is, in fact, a “single-cross” between Kompolti and Fibrimon, but it is the F2 generation which is commercialized. Von Sengbusch and Hoffmann described the phenomenon, but they did not think of its practical use. In Kompolt we make the cross between Kompolti and Fibrimon on a surface of 5 hectare (ha), this yields 2,500 kg of F1 seed. The F1 seed is sown on a surface of 500 ha, yielding 400,000 kg of F2 seed, which is used to sow 3,000-3,500 ha of fibre hemp. So F1 ratio is five will see 500 (10 to 1) and F2 is 500 to 3,500 (or 3,000) so the ratio is 6 or 7 to 1.
Intervie with Ivan Bocsa, http://druglibrary.org/olsen/hemp/iha/iha01215.html
Fiber hemp grows best in well drained soil that doesn’t crust and that holds moisture within two or three inches of the surface. (154) Illinois experts recommend silt loams and clay loams. (155) Iowa experts emphasize good drainage, (156) noting that soggy soil produces weak fiber. (157) A USDA agronomist declared Missouri’s soil and climate “favorable” for commercial hemp. (158) In the 1940’s , northwest and southeast Missouri were considered the best areas in the state for commercial hemp production. (159) An acre that produces 75-80 bushels of corn can produce 2.5-3.0 tons of hemp, (160) but land that produces slightly lower corn yields may produce far lower hemp yields. (161) Fertility is crucial to hemp yield.
Although nitrogen appears unimportant to growth of wild hemp (162), good nitrogen supply improves yields of cultivated stalk. Commercial nitrogen fertilizer works, and so does crop rotation. (163) Planting hemp after alfalfa or clover works well, planting after soybeans helps to a lesser extent. (164) Phosphorus and potassium can be helpful, and manure is universally recommended. (165) Authorities note, however, that fertilizers may increase yield of stalk but decrease yield and quality of fiber from the stalk, (166) thus fertilizer application requires knowledgeable judgment. Although hemp crops remove quite a bit of nutrient, (167) hemp sheds leaves that return nutrients to the field, and upper leaves remaining on stalks drop to the ground as part of the field “retting” process described below. (168) In field retting the soil also recovers about 20% (by weight) of organic material from stalks, and farmers can plow stubble under. (169) Hemp’s net extraction from soil fertility is thereby less than many other crops (170) and is considered comparable to corn. (171) Corn, incidentally, does well when planted after hemp. (172) During the 1970’s in France winter wheat commonly followed hemp. (173) French growers find that hemp clears weeds and cereal parasites from wheat fields, and the deep hemp roots help with tilling. (174) Hemp crops are noted for improving physical condition of soil. (175) Indeed, hemp has been recommended as a crop for soil building purposes. (176) U. S. hemp production fell after World War II because planted acreage fell, not because soil fertility declined. (177)
Fields can be plowed in fall or spring, though some authorities recommend fall. Hemp thrives in the type of seedbed prepared for alfalfa. (178) Seed can be broadcast or planted by seed drill no deeper than one inch; drilling improves yield. (179) Seed is about the size of wheat, 44 pounds to the bushel, and 33-55 pounds per acre are recommended for fiber crops. (180) Higher seeding rates don’t increase the yield of stalks per acre, but can increase yield of fiber from stalks. (181) Experiments suggest that treatment with seed disinfectants have small or zero effect on yield. (182) In the Midwest the best time to plant hemp is after oats and before corn. (183) The first week of May may be ideal around Ames, Iowa. (184) Growing season is 120 days.
Hemp grows quickly and reaches heights of 5 to 15 feet; for fiber production, height of 6 to 8 feet and stalk thickness of 0.25 inch is ideal. (185) Fiber hemp is planted in thick stands (20 or more plants per square foot) that smother weeds. Few diseases or pests trouble crops. Once seedlings appear, farmers rarely must do anything until harvest. Hard rain is unlikely to lodge hemp, but strong hail can damage crops (by destroying leaves and thereby harming plant growth). (186) Fiber hemp needs ample moisture, and drought harms crops; a climate with at least 30 inches of annual rainfall is recommended. (187) In the 1920’s authorities reported irrigation to be feasible. (188)
Traditionally in the United States, mills that contracted for crops rented mechanized hemp harvesting equipment to farmers, relieving farmers from the large up-front cash outlay that purchase of such equipment would require. (189) In the 1940’s equipment rental in the federal program was $ 4 to $ 7 per harvested acre, deducted from crop payment by the mill rather than paid up-front by the farmer. (190) Private mills had similar arrangements with their growers. (191) Harvest starts in late August and continues through September. American authorities recommend harvesting while pollen sheds and before seeds form. (192) Before 1967 French growers harvested after seed matured, but French practice now follows the American one. (193)
If harvested stalks are stacked and stored in dry conditions they will keep for years. They do not have to be processed right away. (194)
Normally, harvested fiber stalks must be “retted.” In retting, stalks are commonly left on the ground for weeks or months so weather may start to decompose them, making it easier for breaking and scutching mills to remove fiber from stalks. Field retting is sometimes called dew retting. Heavy dew, “reasonably high” humidity , and intermittent rain are important for field retting. (195) Stalks can also be retted underwater in ponds or tanks. This method produces better fiber than field retting, but in the 1940’s American technology did not make water retting economical in comparison with field retting. (196) Research at Iowa State College established that controlled water retting could be accomplished in 36 hours. (197) The head of the federal hemp program declared in 1944, “If a program of controlled retting can be developed, I am very confident that there is no limit as to the tonnage that can be grown successfully and profitably in this country.” (198) One account from the 1970’s noted a Swedish water retting operation with capacity for 150 tons of stalk at any given time, producing 33 tons of fiber per day. (199) Some work has been done in processing unretted hemp. (200) Retting is universally considered the hardest part of hemp farming, because shrewd judgment is needed to determine when the crop is properly retted. Fiber yields from improperly retted crops are inferior.
In the 1980’s Canadian Hemp Industries Corporation demonstrated a decorticator that stripped fiber from stalks upon harvest in the field without retting. (201) Such technology eliminates the riskiest part of raising hemp fiber crops, making them more economically viable than they were in the 1940’s.
After stalks are field retted, they are bound and shocked. These steps typically occur at the peak of soybean and corn silo filling, and require more labor than corn harvesting, but 1940’s farm operations handled the labor demand. (202) Until around World War I hemp farming was labor intensive, but mechanical harvesters and mill machinery dramatically reduced labor requirements. In the 1920’s mechanized Wisconsin hemp farmers were able to compete with cheap foreign labor. (203) In 1943 a typical Illinois hemp farm required 19.4 man hours per acre for the season. (204)
Farmers send bales of retted stalks to breaking mills.
As a general rule, the higher the yield of stalks per acre, the higher the quality of fiber from that yield. (205)
Although Missouri had large hemp fiber crops in the 1800’s, the last remnants of the state’s hemp production in the 1940’s supplied seed for fiber growers. (206)
Climate and soil types recommended for fiber production are essentially the same for seed production, although ample soil calcium is emphasized for seed. (207)
Seed hemp is commonly planted in hills 4 or 5 feet apart, thinned to 3-5 young plants. (208) Plants become bushy.
With American varieties growing season for seed is at least 180 days. (209) Traditional harvest method is to cut the plants by hand 8-24 inches above the ground, and shock small bundles of them. After drying (a process taking a few days to 3 weeks) each shock is put on a tarpaulin and seeds are manually beaten off with sticks. “While this seems a rather crude way of collecting the seed, it is doubtless the most economical and practical method that may be devised. The seed falls so readily from the dry hemp stalks that it would be impossible to move them without a very great loss. Furthermore, it would be very difficult to handle plants 10 to 14 feet high, with rigid branches 3 to 6 feet in length, so as to feed them to any kind of thrashing machine.” (210) Seed for new crops is sent to a cleaning mill. Seed for oil is shipped to a crusher.
Although traditional U. S. cultivation practice requires farmers to choose between fiber or seed production, foreign seed growers have harvested seed stalks for low grade fiber. (211) Before the mid-1960’s such practice was also traditional among fiber growers in France, where fiber is used for paper rather than textiles, and can therefore be of lower quality. Seed harvested this way is used for animal feed and for planting new crops. (212) American experience indicates that such seed is poor for new crops, however. (213)