February 11, 2020
Editor's note: This is the third article in a three-part series on industrial hemp production in Missouri. It is meant to offer farmers insights on preparation, planting and harvesting this crop in 2020. This article focuses on harvest.
You’ve prepared the soil and planted hempseeds or plants. Now it is time to harvest your crop.
Harvesting can be as simple as using your own combine or as labor-intensive as using your own hands. It all depends on whether you grew hemp for grain, fiber or cannabidiol (CBD).
Hemp grown for seed is ready to harvest between 105 to 115 days after planting. Farmers can expect grain yields of about 1,000 pounds per acre, says Greg Luce, University of Missouri Extension agronomist.
It can be harvested with traditional combine equipment. The seeds are about the size of grain sorghum. Farmers should try to harvest at 20% moisture.
Fiber yields about 5 to 10 tons per acre, Luce says. Hemp grown for fiber takes about 60 growing days before it is ready to harvest. However, harvesting fiber is much like harvesting hay in Missouri.
“You would cut it and leave it lay to rot,” Luce says. “It’s called retting.”
Retting is where the hemp lies in the field for three to four weeks in order to begin the microbial breakdown process that aids the separation of the fiber. This process also could return potassium back to the soil.
Luce says farmers should avoid overcrimping. After several weeks of retting, bale up the hemp. Some end users like it in large square bales, while other prefer large round bales. Farmers should check with their buyer to see how they want the fiber delivered.
Hemp farmers in places such as Kentucky figured out a way to harvest two crops — grain and fiber — with one machine.
An attachment has the header raised to cut the top of the plant for grain, while underneath is a cutter that lays the bottom of the plant down for fiber. However, Luce says farmers can expect to give up some yield. They’ll see about 50% of typical fiber yields and lose 10% on grain yield.
For fiber and grain, the hemp harvest process is agriculturally based, using traditional farm machinery. But when it comes to harvest for CBD, Luce says, it is more horticultural.
Timing of harvest depends on the strain of hemp plant. Farmers should visit with their plant supplier to see estimated flowering dates.
The highest concentrations of CBD and other cannabinoids are found on the trichomes of female plants. These trichomes are hairlike structures and very sticky. Trichomes also produce terpenes and flavonoids that contribute to a plant’s aroma and flavor profile, so pay careful attention to harvesting plants for CBD.
“Most of it is done by hand-cutting,” Luce says. He notes that some Kentucky growers are using mechanization to harvest the whole plant. “But then you’re going to have to remove that concentrated area of the flower for the CBD," he adds.
For the most part, it is a lot of hand labor. In the South, growers are hanging the plants in tobacco barns or open buildings and allowing it to air-dry.
“Missouri has barns and buildings that would allow for this same type of harvesting and drying technique,” he says. The biggest concern with drying is mold.
Farmers should hang it to dry immediately after harvest. It should be in a well-ventilated building where temperatures stay from 60 to 70 degrees F. Don’t crowd plants when hanging as air circulation is critical. Aim to store the plants with 6% to 14% moisture.
The crop requires a higher seeding rate since it is raised for tonnage, and the ideal stem size at harvest is very small, similar to the diameter of a pencil.
There are many areas that need further research and verification for growing hemp. Grower meetings around the state provided some baseline information to get started with industrial hemp. Much fine-tuning will come with more research and greater experience in 2020.
Luce encourages interested growers to start small and grow with an expanded knowledge of what it takes to grow this new crop in Missouri.
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