Sunn Hemp Production Guide
Sunn Hemp is a tropical legume. The seed will germinate at soil temp of 48°F However, the plant grows much better as the soil temperatures and night temperatures are much warmer. Anytime after the last frost will work but waiting for warmer temperatures makes the plant grow much better.
Seeding Rate: Our recommended seeding rate is 15 lbs. for a cover crop and 25 - 30 lbs. per acre for grazing. We start at the low range to save costs for growers. Many growers are upping their seeding rates after seeing the benefits.
Seed Depth: Seed will come up on top of the ground to 2 inches of depth. Planting 1/4 - 1 inch deep is best.
Soil Test: Sunn hemp will grow on a pH from 5.0 - 8.5 so your soil will not need liming for the it to grow. It needs no fertilizer. However, it will grow better if ample Phosphorus and Potash are already in or added to the soil.
Inoculant: In the Southern States, we are not recommending the use of inoculant as there is typically plenty inoculant in our soils. In Northern states sunn hemp is responding to the use of peanut inoculant.
Drought Tolerance: Sunn Hemp grows best on sandy, well drained soil. It does not like hard, packed clay. It does take moisture for it to germinate, and then another good inch of rain to get it going. After that, it is fairly drought tolerant.
Plant growth: For the first 30 days, the plant is sending down roots and top growth is very slow. After that, the plant usually grows rapidly and typically reaches six feet in growth by day 60.
Start of Grazing: We have found the best time to be when the plant is 32 - 36 inches tall. At that time, the livestock will eat the terminal of the plant down to about 18 inches. The stem will bud back ou shortly, making new branches and leaves. This will provide more vegetation for grazing. If grazed too short it will take longer for the plant to regrow. If allowed to get too tall, livestock will typically knock the plant down instead of allowing it to regrow.
Sunn hemp for hay and silage: Yes, this can be done. Best to use a mower conditioner. Cutting the sunn hemp when 4 - 5 feet gives the best quality of hay. Cutting the sunn hemp about 4 inches off of the ground may allow it to regrow if there is plenty of moisture. Making hay or silage from sunn hemp has not been easy, and may be disappointing for you.
Disease: Sunn hemp is fairly resistant to disease. Fusarium wilt is the most common to affect it. Rotation is a must. After growing sunn hemp for two seasons, it is best to rotate to another crop.
Insects: Although sunn hemp does attract grasshoppers and other insects, they are rarely a problem. Even if the grasshoppers or army worms completely defoliate the plant, the leaves will grow back. Seldom has anyone benefited by by spraying for insects on sunn hemp.
Weed Control: This crop may prove very beneficial in ridding land of unwanted weeds. Sunn hemp does have allelopathic activity on some weeds, including palmer amaranth and its very rapid growth almost totally chokes out other weeds. It appears to smother out most if not all other weeds including pig weed, palmer amaranth, and nutsedge.
Nematode Control: Sunn hemp is resistant to root-knot and Reiniform nematodes. Root-knot and Reiniform nematodes are a major pest in South Alabama agriculture. And root-knot nematodes are a pest in almost every home garden in South Alabama. Sunn hemp would be a tremendous benefit in reducing nematode populations in almost every home garden in our area. Gardeners could plant their spring crop and then in June, July, or August plant the sunn hemp.
Termination: For a cover crop, it is best to let sunn hemp grow from 60 - 90 days before terminating. At six feet tall there is usually a perfect Carbon/Nitrogen ratio in the plant. If allowed to grow longer the plant will produce more Nitrogen, but will also produce more Carbon. The Carbon fiber in the plant may tie up the Nitrogen in your soil for a few months.
Not an invasive weed: The sunn hemp will not flower and go to seed until the days start getting shorter (mid-September here). After flowering there is not enough time for those seeds to mature in our area.
Sunn hemp is perfect for the home gardener, organic farmer, row crop, turf, wildlife and livestock farmer. We encourage you to give it a try on your farm.