For optimum germination, industrial hemp seed requires good seed-to-soil contact. The seedbed should be firm, level and relatively fine; similar to that prepared for direct-seeded forages. The soil can be worked and planted as soon as the ground is dry enough to avoid compaction. A shallow, firm seedbed allows seed to be placed at a uniform depth, resulting in a more even seedling emergence. Industrial hemp is normally sown using a standard grain drill. Plant seed at a depth of 2-3 cm. Optimum soil temperature at that depth for fast germination is 8-10oC, although hemp seed will germinate at 4-6oC.
Industrial hemp that is planted for fibre is usually sown in 15-18 cm (6-7-in.) rows, using every run of the drill. Optimum final stand is about 200-250 plants/m2. Early seeding (as soon as soil conditions are appropriate) is recommended. Researchers recommend a minimum seeding rate of 250 seeds per m2. Planting rate is recommended at 45 kg/ha. This could be higher if germination is low and seed is large. Table 2 shows how the seeding rate changes according to seed size and density (weight per 1000 seeds) for most varieties. Seed density is specific to each variety, and is more or less constant from year to year. Seed density information should be available from the seed supplier.
Industrial hemp is day-length sensitive, resulting in greater vegetative growth if planted earlier, as shown in Figure 6. As days become shorter, 4-5 weeks after the summer solstice (June 21) vegetative growth slows and flower development is triggered. Early planting takes advantage of this feature, resulting in taller plants with higher fibre yields. This does not change the cutting date significantly.
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.