The hard work of planting thousands of hemp seedlings into carefully cultivated fields will soon be over. We've come a long way baby, since planning, tillage and greenhouse time, and in just a few short weeks the crew shifts gear to feed and nurture a magnificent crop.
It takes regular crop monitoring, and proper timing to beat the weeds and ensure you’re meeting the plants’ water and nutrient needs. Each of the topics addressed in this article would take volumes to explore fully, so consider this as a primer to identify basic requirements and help hemp growers establish a beneficial routine.
A successful strategy begins with the decisions you make about the layout of your crop in the field (which we covered here). Other aspects of your combat plan include the use of mulches and cover crops, irrigation, and the timing and types of fertilizers and nutrient delivery methods you plan to use. Let’s dive in.
One of the most important decisions you'll make as a Vermont hemp farmer, is the choice of mulch for your crop. Mulch is your first line of defense in order to:
- Regulate soil temperature and moisture around the plants and in the aisles,
- Support microbial activity in the topsoil,
- Prevent erosion,
- And reduce weed pressure.
The choices of mulch for growing high-CBD hemp are generally sheet mulch, straw or another local plant-based material. Using sheet plastic for mulch is not a requirement of growing a successful hemp crop, but for convenience, and effectiveness most hemp growers in Vermont and the region mulch their rows of plants with sheet film (poly or biodegradable). The large rolls are best applied with a mechanized plastic mulch layer, and if you’re a certified Organic grower check to confirm the film you use is NOP compliant. Also, keep in mind that laying plastic requires installing drip irrigation under the film.
Our experience has shown that once your transplants are in, seeding a cover crop in the aisles between the planted and mulched rows accomplishes several things. For instance, a clover and vetch mix keep the soil cool, moist and productive, fixes nitrogen, builds organic matter, and controls erosion during the length of the growing season. Alternatively, other growers use straw, felt, film or biodegradable sheet goods in the aisles.
Once the cover crop is established, mowing the aisles every 2-3 weeks will keep growth under control. Even if you're growing using conventional methods, you will have to control weeds using a combination of mulch and mechanical means, since there are no approved herbicides for hemp.
One tool we recommend keeping out of the hemp field is the weed wacker. Although it might be tempting to use a string trimmer between the plants, the amount of dirt and plant debris thrown onto the flowering branches, and the potential for spreading mold spores and fungus outweigh the convenience.
Although hemp is drought tolerant, either ample rainfall (at least 20 inches) or irrigation are needed for the plants to thrive. If you use plastic mulch, you will have to irrigate. Investing in buried pipes from your water source and laying out drip lines under the plastic is the usual course. University of Vermont research has shown that irrigated hemp can outperform exclusively rain-fed crops by almost 2:1 (see "Hemp production 101" starting at 1:25:00).
Seedlings are especially vulnerable during the first six weeks after transplanting and should be well watered. It's just as important that the crop doesn't have perpetually "wet feet", so it’s okay to let the soil dry out periodically.
For hemp growers starting with a small field and mulching with plant-derived materials you have a choice. Install drip irrigation or use a pickup or tractor to drive a poly water tank, 12-volt pump and hose down the aisles to irrigate.
Feeding in the field begins when the seedlings are transplanted and continues until the last two weeks before harvest, with the nutrient needs of hemp changing as the plants mature.
Use a mix tank and fertilize with the macronutrients, N-P-K (nitrogen, phosphorus, potassium) for those set up with drip irrigation. We recommend a light nitrogen boost and adding liquified kelp in the mix tank when first watering-in the transplants. Kelp provides essential minerals and micronutrients (boron, copper, iron, etc.), and the nitrogen perks up the seedlings and reduces shock.
During the seedling stage, this is the time to begin introducing soil microbes, inoculants, and mycorrhiza. These important allies aid in the plants' ability to assimilate and circulate the macro- and micronutrients. Replenish the microbes about once a month; many of them only have a 3 to 4-week life cycle.
Foliar feeding with a sprayer can also be beneficial, especially when the plants are young and before their root systems are well developed. You can also apply liquid or granular fertilizer at the base of the plant by hand if growing on a smaller scale. And remember fellow farmers, more is not better; for proper application always follow the product labels.
A final and important note on applying nutrients is this: once a majority of the plants have begun flowering, back off on the nitrogen feeding while adding and increasing phosphorus and potassium. After a couple of weeks of tapering, there should be no more nitrogen going to the plants, and you should be applying P and K at the full recommended levels. About two weeks before harvest, stop all nutrients and water as usual to help "flush" the plant system of residual N, P, K, and minerals.
We'll be back next week to discuss how to identify and treat for pests you may encounter encroaching on your hemp crop. As always, please leave your comments or questions below. We enjoy hearing from you!