Industrial hemp can be grown on very different types of soil and it is considered very durable and adaptable, as the cultivated varieties have not been very 'domesticated' yet (Montford, S., Small, E., 1999). Scarified permeable loam with high fertility and plenty of organic material is considered the most suitable soil (Bocsa & Karus, 1998, cit. Barron, A., 2003). The plant prefers adequately deep well aerated soil with a pH ranging from 6.0 to 7.5. Hemp is sensitive to floods, badly aerated thick soil and heavy soils. Therefore field drainage is essential. Attempts to grow hemp in low-lying areas and on heavy soils have shown that the length of the stem (biomass) might remain the same but the quality of the fibre decreases (Barron, A., et al. 2003).
Hemp adapts well to different climates and is can grow in very diverse environmental conditions. The best growth temperature for hemp is 14 to 27°C but it can withstand colder and warmer climates and is somewhat tolerant to night frost (Callaway, J.,C., Hemmilä, A.,M. 1995). An old hemp plant can withstand temperatures as low as –6°C. Varieties suitable for growing in the Nordic countries require a 90 to 120 day growth period and a germination temperature of over 10°C.
Fibre hemp field (Estonia, 2005)
Hemp plants need plenty of water during the first 6 weeks. If the plants are well-rooted, they will manage in dryer conditions. Severe drought makes the plants mature faster and therefore dwarf plants may occur (Barron, A., et al. 2003). Hemp requires on average 500 to 700 mm moisture for optimal growth and 250 to 300 mm moisture for the vegetative period; this includes both precipitation and soil moisture. The hemp grown in Europe is largely dependent on the rainfall of June and July. Hemp is one of the most drought-tolerant species but also reacts well to watering, which is especially important for producing seeds.
Because the plant grows fast, the soil has to have plenty of nutrients and they have to be accessible. Hemp's nutritional needs are considerable, especially during the vegetative period.
Plant growth is divided into 6 phases (Bocsa & Karus, 1998, cit. Barron, 2003):
- Slow growth period that lasts from the emergence of the first leaves until the formation of the fifth leaf pair
- Fast growth period that lasts until the formation of buds
- Formation of buds until the emergence of the first flowers
- Flowering period
- Seed formation