The effective accumulated temperature of 2400-3200 ℃ is required for the growth and development of cannabis. The seedlings can tolerate frost at – 5 – 3 ℃, and low temperature for a short time will not affect the growth of hemp seedlings.
Cannabis is sown when the soil temperature is above 8 ℃ at 5cm below the ground surface in early spring. Within 30 days after the emergence of hemp seedlings, most of them will not be irrigated, and LED plant growth lights will be used to promote the growth of hemp seedlings to control seedlings and promote roots.
According to the morphological differences between male and female seedlings, male seedlings can be selected and removed during seedling fixation to improve fiber quality. For seed collection in hemp fields, female seedlings are kept.
The suitable temperature for hemp growth is 19-23 ℃. The average daily growth of hemp plants is 3-5 cm, and the growth peak can reach about 10 cm. At this time, it can withstand atmospheric drought but not soil drought.Therefore, it is usually started to irrigate continuously after one month of seedling emergence to keep the maximum soil water holding capacity at about 80%.
Early application and repeated application of quick acting fertilizer combined with irrigation can promote stem growth. The density of seedlings retained varies with different cultivation methods. Generally, early maturing varieties retain 8-150000 seedlings per mu, and late maturing varieties retain 30-50000 seedlings.