May and June are optimal planting months but some cultivars can be set in the field as late as early- to mid-July and still be expected to produce smaller, but reasonable, flower yields.
Figure 1. Hemp seedlings started in a greenhouse showing two sets of true leaves. These plants could be transplanted into the field if environmental conditions are appropriate. (Photo by Jonathan Palmer)
Most organic producers will create a tilled seedbed for their crop. Hemp cultivars grown for cannabinoids are bushy and branched. Field spacing varies depending on cultivar, planting stock or individual grower needs. Typical in-row spacing between plants ranges from 3.5 feet to 6 feet. Smaller spacing is used when male plants will be culled from the field (see below). Spacing between rows depends on planting methods, weed control strategies, and equipment but generally ranges from 5 to 7 feet. Growers often set plants by hand or use a waterwheel or other horticultural transplanter with or without a plastic layer. To prevent stem disease, the rootball should not be set deeper than 0.25 inch below field surface. Some growers use raised or mounded beds to enhance drainage and aeration. Drip irrigation systems help to provide water while transplants become established in the field. After root systems are well developed, many Kentucky growers find the need to supplement water during prolonged dry periods.
A major concern in organic systems is weed control. Some growers control weeds by planting in plastic mulch which is acceptable in organic production as long as the materials are petroleum based (no PVC) and are removed from the field after the season. Other growers dislike plastic because it can fragment over the course of a season, is laborious to remove, and the waste ends up in landfills. Organic growers should manage weeds through a systems approach involving weed suppressive cover crops prior to hemp, tillage, stale seed-bed techniques, and mechanical or hand cultivation within and between rows during the season. Weed control is critical during establishment of new plants and through early growth. As hemp plants mature and establish a canopy, the need for cultivation within rows decreases.
Other growers dislike plastic because it can fragment over the course of a season, is laborious to remove, and the waste ends up in landfills. Organic growers should manage weeds through a systems approach involving weed suppressive cover crops prior to hemp, tillage, stale seed-bed techniques, and mechanical or hand cultivation within and between rows during the season. Weed control is critical during establishment of new plants and through early growth. As hemp plants mature and establish a canopy, the need for cultivation within rows decreases.
Figure 2. A field showing well developed female hemp flowers in an organic cannabinoid crop. (Photo by Shawn Lucas)
Hemp has two primary stages in its life cycle: vegetative growth where plants basically get bigger and reproductive growth where plants produce flowers. Most hemp cultivars develop male and female flowers on separate plants. Concentrations of CBD and other cannabinoids, including THC, are highest in mature female flowers (Figure 2) which are the raw product of a cannabinoid crop. Hemp plants are generally photoperiod dependent, flowering based on the hours of daylight available.