Growing Healthy Hemp Plants
With hemp becoming a major cash crop, whether for CBD oil or fiber, many cultivators are now growing the plant. Starting with seed selection, Chris Bond elaborates on what’s needed to grow healthy hemp plants for crop production.
The re-emergence of hemp as a viable commercial crop has shaken up the traditional agriculture world. The prospect of raising a lucrative crop has individuals who have never put a shovel into the ground imagining themselves to be farmers.
Hemp may well be a profitable crop with yet unknown earning potential, but to fully realize its potential, it’s important to try to raise the biggest, healthiest, and prolific plants for your individual region. For those who may be unclear what makes cannabis hemp and not, well, weed, it is important to understand a few basic concepts.
In a nutshell, hemp is cannabis with THC levels of less than 0.3 per cent, meaning it is not grown as either medical or recreational marijuana, since it has no hallucinogenic attributes.
Cultivation of hemp is very similar to that of other cannabis because it is essentially the same plant, just with different properties. Hemp is an annual, broadleaf plant capable of rapid growth under ideal growing conditions. Except in research settings, it is grown in the field.
As of the time of this writing it is not legal for the average grower to grow hemp entirely under cover in a greenhouse or high tunnel setting. It is, however, legal to start the crop inside and then transplant out into the field by a certain date usually established by each state’s department of agriculture.
Hemp is grown for several reasons, but predominantly for either its fiber, flower, or seed.
Read also: The Hemp Revival: Why the World is Seeing More Hemp-based Products on the Market
Like other cannabis species, hemp is dioecious, meaning plants can be either male or female. In most applications, the female varieties are preferred and cultivated. To minimize the chance of this outcome, most hemp cultivars are bred to be mostly female (monoecious). The female flowers and seed set are indeterminate, meaning the seeds continue to develop and mature over an extended period.
Another emerging type of hemp is the Female Predominant which is generally 85 to 90 per cent female, meaning male plants will need to be culled, but these types typically produce higher yields than straight monoecious types.
To say the least, it is important to know what the desired outcome is before selecting your seed.
Hemp Seed Selection
Before purchasing seeds for hemp production, it is important to realize there are hundreds of types out there. Some varieties are better for fiber, some for oil, some for flowers, and some for dual purposes. Fiber varieties tend to mature between 60 and 90 days while grain and oil types typically mature between 100 and 150 days.
Besides selecting a proper cultivar based on its purpose, yield potential, and THC levels, it is equally important to select seeds that will produce plants hardy for the region they will be grown in. For help in selecting a type appropriate for your region, state departments of agriculture usually provide a list of appropriate cultivars for your region and hardiness zone.
Be wary of recommendations found via online message boards and other biased sources. There is still a lot of research to be done on the best strains for each region, but there is enough information out there to make an informed choice with some peer-reviewed data behind it to give a fair estimate of a species’ expected results.
Read also: Foolproof Hemp Cloning
Direct Seeding of Hemp
Depending on the type of seed selected, the desired purpose of the crop, and the region where it is grown, hemp seeds will either be directly seeded into the ground or started under cover and transplanted into the field after the threat of frost has passed. Average seeding rates for fiber crops are about 50-100 lbs/acre (55-110 kg/ha) and 20-50 lbs/acre (22-56 kg/ha) for grain types.
Before seeding hemp, it is imperative to properly prepare the seedbed. When possible, the field areas should be plowed up in autumn before spring planting. The planting area should be prepped into a level and firm seedbed.
Optimal germination will be achieved by good seed-to-soil contact when soil temperatures reach 45-50°F (7-10°C). When you are ready to seed your hemp, plan on seeding to a depth between 0.75 and 1.25 inches (2-3 cm). The actual depth will be specific to each variety.
Hemp seed can be installed with a standard grain drill. When proper conditions have been met, hemp seed will germinate quickly. Expect to achieve heights of about 12 inches (300 mm) in three to four weeks from planting. At this stage it will provide up to 90 per cent ground shade and suppress the growth of competing weeds.
Seedlings and Care
In most parts of the country that have a last frost date from mid to late spring, hemp is seeded indoors in a greenhouse setting and then transplanted out into the field. Unlike field seeding, greenhouse hemp seeding is usually done by hand and each seed is placed in an individual cell or pot.
It is likely each plant will have to be transplanted into bigger cell or pot sizes before it is warm enough to transplant into the field, but this is predicated on what region of the country you are in and how robust the strain of hemp you have selected is performing.
During this indoor growth period, it is important to attend to hemp’s light, heat, and nutrient needs carefully. The focus will be on vegetative growth and not flower production. For this reason, it is important the seedlings receive at least 12 hours per day of either natural (preferable) or artificial lighting. During this period daytime temperatures should be in the range of about 77-82°F (25-28°C) and nighttime lows should not dip below 65°F (18°C).
An entire article unto itself could be (and likely will be) devoted to the nutritional needs of hemp seedlings grown in a greenhouse. At a minimum, know that the nutritional needs of hemp will change during different developmental stages and it is important to cater to each at the appropriate times. This will also change based upon how the plants are being grown and in what media.
To further complicate things, it will depend on how long the plants are to remain inside before being transplanted. It is critical to regularly monitor both the pH levels and the EC levels of your greenhouse seedlings and take appropriate remedial measures when warranted. In general, though, pH levels should be on the acidic side, but not below 6.0 and the EC will depend on the strain, but it should not fall below 1.0 or be more than 2.5. Again, each individual strain has its own ideal ranges and the nutrient levels should be adjusted accordingly during the greenhouse stage of your hemp grow.
Read also: What are the Best pH Levels for Growing Cannabis?
Field Cultivation and Care
It is a common misconception that hemp can be grown just about anywhere. While it is easier to grow than some other crops, there are specific pH, soil, nutrient, and even light requirements it needs in order thrive.
Hemp, like many other crops likes to be grown in a loose, aerated loamy soil. Soils too high in clay will be poorly drained and sandy soils will require additional irrigation to keep your hemp crop properly hydrated.
Hemp, like many other crops that prefer a slightly acidic to neutral soil, can do fine between the range of 6.0 to 7.5. Wait until field soil temperatures are at least 45°F (7°C) before planting out and ideally not until they have reached 50°F (7-10°C). A good rule of thumb is to plant hemp just before corn is planted in your area.
If adequate rainfall isn’t present, then irrigation will be necessary, especially during the first 30-60 days of establishment while they are rooting into your soil. Plan on your hemp crop receiving at least 25–30 inches (635- 760 mm) of rainfall or prepare to provide some supplemental irrigation. Hemp requires lots of moisture. A significant portion is required at the outset to provide early ground cover to out-compete field weeds and reduce the amount of surface evaporation. About half of the water needed is on the back end, during flowering and seed set. Make sure your hemp crop receives at least 10-13 inches (300-400 mm) during this time period.
Hemp crops require approximately the same amount of nutrients/fertilizers that a crop of corn or wheat would need. Actual inputs in each individual situation should be calculated based on soil analysis results, but the following guidelines show the needed ranges of nutrients for a successful hemp crop:
- Nitrogen (N): 100-130 lbs/acre or 130-145 kg/ha
- Phosphorus (P available as P205): 45-70 lbs/acre or 50-80 kg/ha
- Potassium or potash (K available as K2O5): 35-80 lbs/acre or 40-90 kg/ha
- Sulfur (S) should be present at levels above 5,000 ppm
- Calcium should be present not more than 6,000 ppm
Another often overlooked consideration is balancing the nutrient needs with each other. If economic considerations limit the ability to apply the needed nutrients in their full quantities, it is better to apply some of each rather than all of some and not others.
For example, if only the amount of nitrogen is provided without ensuring appropriate potassium levels, it could be more damaging than applying none since this could lead to stalk breakage and total crop loss in extreme cases.
Additionally, organic matter should be greater than 3.5 per cent. This should be easy to maintain with successive crops as well over one-third of the plants’ biomass can be returned to the soil after harvest. Some of the stored nutrients in the leaves, roots, and other debris will be available the following season when it is tilled back into the soil.
Although once planted in the field, there is little that can be done to control the amount of light your crop receives especially when planting multiple acres. It is important however to remember industrial hemp is a day-length sensitive crop. More vegetative growth will occur the longer the amount of daylight. After the Summer Solstice, flower development is triggered. This can of course all be manipulated by adjusting the seeding date accordingly for either direct-seed or greenhouse grown seedlings.
Read also: 5 Things To Know Before You Plant Hemp
Hemp Pests and Diseases
Like any other cultivated crop, hemp is prone to pests and diseases. Controlling the environment is the best way to realize healthy hemp plants. Because hemp has only really been commercially grown in the US since 2014 (pre 1930s notwithstanding) not all pathogens have been fully identified.
As production increases, it is very likely more pests and diseases will emerge. Currently though, known insect pests of hemp include European corn borer, armyworm, and even grasshoppers. There are more diseases of hemp than insects.
Common diseases include fungal pathogens like gray and white molds (Botrytis cinerea and Sclerotinia sclerotiorum) and pink mold (Fusarium), as well as bacterial leaf spots, viruses, root rot, and blight.
Unfortunately, there are no pesticides registered for use in hemp production in the US. Crop rotation and selection of disease resistant varieties is currently the best way to keep your hemp crops healthy and realize maximum yields.
To reduce the likelihood of diseases remaining in the soil, that can be transferred onto your hemp crop, do not grow hemp in the same fields directly following canola, beans, or sunflowers. Sclerotinia occurs about 10 per cent of the time when hemp follows canola.
Finally, it bears repeating that before doing anything regarding hemp production, perform a soil test. It is relatively inexpensive and will provide a wealth of valuable data into your soil type and attributes as well as your existing nutrient profile. At the very least it will tell you if your soil is suitable for hemp production and has the potential to save many thousands of dollars in unneeded nutrient inputs if they are already there.
Written by Chris Bond | Certified Permaculture Designer, Nursery Technician, Nursery Professional
Chris Bond’s research interests are with sustainable agriculture, biological pest control, and alternative growing methods. He is a certified permaculture designer and certified nursery technician in Ohio and a certified nursery professional in New York, where he got his start in growing.