Planting - Hemp seeds can be used as a cover crop or as a rotation crop. It can be scattered or drilled, but ideal planting depth is ½”-¾”. Fiber production is best done with 35-50 lbs of seed, drilled.
Lowest Soil Temp - 46-50 degrees
Fertilization Requirements - For a crop with a 1,500-lb yield potential:
- 150 lbs nitrogen
- 30 lbs phosphate
- 20 lbs potash
Planting Rates: Planting rates for industrial hemp depends on the variety, but in general rates from 25 to 35 pounds per acre are recommended. Planting depth should be ½ to ¾ inch. A dense, drilled stand should provide some control for weeds. (Pennsylvania)
Hemp Growth and Development: Hemp is a short day plant. Short-day plants develop flowers only when the day length is less than about 12 hours (about August in Indiana). For best results in Indiana, earlier planting will promote greater vegetative growth resulting in more robust plants for seed, and in taller plants with higher fiber yields. Days begin to get shorter after June 21st, and approximately four to five weeks after this date, vegetative growth slows and flower development is triggered.
Hemp grows best on a loose, well-aerated loam soil with high fertility and abundant organic matter, with a pH of 6.0-7.5. Well-drained or tiled clay soils can be used, but poorly-drained clay or poorly structured soils often results in establishment failures, as seedling and young plants are prone to damping-off. Sandy soils can grow good hemp with adequate irrigation and fertilization but these additional costs often makes production uneconomical.
Planting Date: Although the seedlings will germinate and survive at temperatures just above freezing, soil temperatures of 46°–50°F are preferable. Generally hemp should be planted after danger of hard freezes, and slightly before the planting date of corn. Good soil moisture is necessary for seed germination, and plenty of rainfall is needed for good growth, especially during the first six weeks, for establishment. Rainfall should be about 25-30 inches per year, but is most important in the first six weeks.
Planting Depth: Seedbed preparation requires considerable effort. Fall plowing is recommended, followed by careful preparation of a seedbed in the spring. The seedbed should be fine, level, and firm. Seed is best planted at 0.75-1.25 in (although deeper plantings will be tolerated, they are more susceptible to damping-off).
Plant Rate and Row Width. Seeding rate is specific to each variety, and this information should be sought from the supplier. Industrial hemp is normally planted using a standard grain drill. Both oil and fiber hemp is typically planted in 6-7-in. rows, using every run of the drill.
Oil Seed: As per other seed crops, plants are direct seeded at a rate of approximately 25-40 lb/acre. There are approximately 27,000 seeds per pound. Competition between plants is minimized to produce the highest quality seed and oil. For grain production, desired final plant population is around 10-15 plants/sq. ft.
Fiber: Fiber crops are planted at a rate of approximately 40-80 lbs per acre. This high density is better for producing higher quality primary bast fibers instead of core fibers. The bast fiber content increases with plant density, but optimal densities have not yet been established. Large quantities of hemp seeds must be planted to establish optimal crop density, and suppress weed competition. However, it is important to recognize that difficulties may also result from plant competition. Final stand density should be approximately 30-35 plants per square foot for fiber.
Hybrid: Densities for seed production for tall, European, dual-purpose cultivars are less than for short oilseed cultivars.
When hemp is planted on good draining, fertile loam with appropriate temperature and moisture conditions, seed will germinate quickly and reach 12 inches in 3-4 weeks from planting. At this stage it will give 90% ground shade and suppress the growth of weeds by shading. Rapidly growing hemp at a density of approximately 20 plants/sq ft, will suppress nearly all weed growth.
Fertility: Hemp production does better with 100-130 lb of additional nitrogen/ acre, 45-70 lb/acre phosphorus, and 35-80 lb/acre of potash (to keep potassium levels in a medium to high range of >250 ppm). Phosphorus levels should be medium to high (>40 ppm), sulfur good (>5,000 ppm), and calcium not in excess (<6,000 ppm). In addition to well aerated, loamy soils, hemp does best when organic matter greater than 3.5%.
Environmental Impacts of Hemp:
- Soil Ecology
- Crop Yields
- Soil Compaction
Ecology & Compaction: Soil organic matter restoration: Because hemp has such an extensive root system it leaves behind significantly more soil organic matter after being harvested. Overtime, like other plant roots, hemp’s roots also decompose with the help of healthy soil bacteria. However, unlike other decomposing root systems hemp restores not just net more soil organic material to the soil, which will help crops the following year, but hemp gets restores soil nutrients in lower levels of soil, which also helps soil compaction issues.
Restoring organic material is certainly good for soil ecology, but hemp takes it a step further. Hemp roots are the densest within the first 12” to 20” of the soil. The reason this is important to note is because corn and soy both have roots that average between 12”-24” meaning the roots don’t just contribute organic material to the soil but after decomposition it leaves nutrients at an ideal depth for Iowa’s other major crops, which will help make crop projections more reliable and also larger. Additionally, when hemp matures and is ready for harvest. These leaves then decay restoring more nutrients to surface soil, which can help plants establish stronger root systems before growing deeper.
Water: Hemp has been used as a phytoremediator since the at least the 1900s. In fact, the UDSA has research programs on hemp’s remediation abilities dating back to before the 1930s – more than 75 years.
Phytoremediation will really be the big player of hemp’s ability to restore Iowa’s water quality. Most of Iowa’s water pollution is from rural nutrient runoff, which can hurt Iowa’s marine life, ecosystems in the Gulf of Mexico on which Americans rely to make a living, and the drinking water quality of our friends and neighbors. Part of the reason rural runoff is a culprit is because of over fertilization because crops are not efficiently using nutrients given to them. This is because one of the effects of soil compaction is that the hydrodynamics of compacted soils change and that restricts proper and effective movement of air, moisture and nutrients in the soil and the excess nutrients runoff into the water resources or seep down into water tables and aquifers that are shared with our neighboring states.
Hemp phytoremediation water quality improvement projects are already being implemented and researched in the US. In 2012, Colorado began the implementation of a hemp phytoremediaiton project in response to its’ own soil and water problems in response to their farming nutrient runoff and soil productivity problems. The state of Hawaii has also been conducting ongoing hemp soil quality, erosion and remediation since the 1990s and earlier.