How to Cultivate Hemp

Hemp Cultivation & Germination

How big will they get?

The answer to the question, “How big will my hemp plants grow?”, depends mostly on when they are planted and how big they are when put in the ground. Once cannabis sets bud, its vegetative growth slows while it devotes its energy to producing flower. Four to six weeks after showing bud, vertical and horizontal vegetative growth will slow and eventually stop. If you’re just learning how to cultivate hemp, keep in mind that as the plant continues to mature, most of the leaves will fall off and the plant will look completely different with long thick colas.

Growth cycle and photoperiod

When learning how to cultivate hemp, it’s important to understand the growth cycle of the hemp. Indoor cannabis growers divide the growth cycle into vegetative and flowering phases. The vegetative phase starts when the hemp seed germinates and starts to establish roots. After four or five nodes grow they really kick it into gear under 18 to 24 hours of light. With this much light per day, the plants will keep growing, getting taller and bushier. The vegetative stage can be sustained for months under these conditions.

Indoor growers induce the flowering phase by reducing the light to 12 hours a day. The females will immediately start the flowering cycle because of the abrupt change in photoperiod. Vegetative growth starts to slow as most cannabis strains show bud in two weeks. By the start of week six in flower, the buds will be large, sticky and still maturing.  Most hemp strains grown indoors will be approaching the 0.3% THC limit at this point.

Hemp cultivation and germination out in the hemp fields is a bit different, as Mother Nature controls the light of course. There are four basic climactic/photoperiod zones, mirrored in the northern and southern hemispheres. Equatorial, subtropical, temperate and arctic/antarctic. The Florida peninsula and southern Texas are in the subtropical zone, the rest of the US and the lower Canadian provinces are in the temperate zone (30 to 60 N latitude). The subtropical zone has spring and fall cannabis growing seasons while the temperate zone has one summer growing season.

If you are cultivating medical or recreational hemp, it’s important to note that change in photoperiod is the primary factor that triggers the flowering stage of cannabis’ growth cycle. The photoperiod of June 21, the summer solstice, is the longest of the year in the Northern hemisphere.  Around latitude 40 N, the day will be almost 15 hours long, by July 21, less than 14 1/2 hours, and bud should be setting. The flowering and maturation process is mysterious and many factors and contingencies are involved including moon phases. Before hemp cultivation or germination takes place, it’s important to consult the Farmer’s Almanac for best planting and harvesting times for your locality.

‘Vegging’ before transplanting to a hemp field

When explaining how to cultivate hemp, we need to discuss the vegging state of the hemp. Most high-CBD hemp growers won’t plant a seed directly in the ground.  If you go through the expense and work to set up a drip hemp field irrigation system on 5 or 6 foot centers, a thriving plant should be transplanted at each site.  Growers will transplant anything from a starter plug to 6 inch rockwool cubes or 1 gallon pots.  But the bigger a plant grows in the vegetative stage before transplanting to the field will determine it’s size and weight at harvest, which is yield.

The most practical way to ‘veg’ plants during hemp cultivation and germination is in a greenhouse or hoop house.  Trays of plugs can only be grown for a limited time before they stretch and get weak, plus they constantly dry out their media if they get too big. Transplanting plugs or seeding in 3″ to 6″ pots or rockwool will allow them to grow normally with limited stress for a few weeks before transplanting to the field.  The size of the pots or media will determine how many square feet of hoop or green houses needed.  The media size also determines how long the plants can veg and how big they can get before transplanting to the field.  When cultivating hemp, timing is critical at this stage.

Artificial light

Some kind of artificial light is recommended during the hoop/green house vegging process.  Keep the plants in a vegetative state during this period. This can be guaranteed by making sure they are lighted 16 to 18 hours a day. ​This will ensure they grow vigorously for a few weeks after transplanting to the field, before the flowering cycle kicks in.

A hoop/green house with double-ended HID bulbs will produce big, strong plants quickly. At 40 N latitude, on April 15th the photoperiod is about 13 hours. Artificial light would be required for 5 hours, good growers will run an extra hour or two after sunrise and before sunset for enhanced growth. Intense artificial lighting during recreational or medical hemp cultivation is not required to keep plants in a vegetative state though, flood lights are sufficient light to prevent flowering, but they won’t contribute to any growth.