Sunn Hemp for Home Gardens | Gardening in the Panhandle

A Sea of Yellow

You do not often see a sea of yellow flowers on what was recently a field of row crops in North Florida. In this instance, the culprit is a cover crop called sunn hemp (Crotalaria juncea). Cover cropping, or green manure as it is sometimes known, is not a new concept. It is a great method for improving soil quality, adding organic matter, augmenting nitrogen supply, supporting pollinators when resources begin to wane, and combating nematodes. Incorporating this sustainable agriculture practice into home vegetable gardens is an excellent method to build long-term viability and production.

Many plants may be used in this capacity, but this article will focus on sunn hemp. This annual is an herbaceous, short-day flowering plant in the Lamiaceae or legume family. Its erect stems produce a great deal of biomass and, as a legume, will augment nitrogen stores within your soil profile. As if that wasn’t enough to sell you, this plant is also known to suppress nematode populations. Native to India and Pakistan, where sunn hemp is grown for fiber, this plant grows well in tropical and temperate environments. It will thrive in even sub-par conditions and requires little fertilizer input.

UF/IFAS Photo: Josh Criss

Seed Time

Seed this plant once your summer gardens have begun to wane. The shorter day length will keep the plant confined to about 3-4 feet while still allowing it to flower. It may also be planted earlier in the year to maximize below-ground biomass and add organic matter. In this scenario, the plant will likely grow to 7 feet tall with a closed canopy within 10 weeks.

Sunn hemp requires little fertilization as it is a legume, a plant family known to fix nitrogen from the atmosphere. This same mechanism is one of the features of this plant as a cover or green manure crop, as it can add up to 320 pounds of nitrogen per acre back to the soil when planted en masse.

Seeding rates within a home garden are much smaller. A farmer may plant 30-50 pounds of seed, which is not practical in small-scale growing. Instead, aim to cover the garden area through broadcasting seed, as a denser planting will reduce the later branching of this plant. Ensure you have 8-12 weeks of warm, frost-free weather, and terminate them prior to reaching the full bloom stage. Doing so will provide your gardens with the same benefits seen in farm fields utilizing this sustainable practice.

UF/IFAS Photo: Josh Criss

To Sum it Up

Sunn hemp is an excellent plant for your gardens before your fall greens. The biomass it produces and the nitrogen it recovers make it very attractive to farmers and should raise eyebrows even in the home garden. The trick is learning to manage this plant within your crop rotation. For more information on soil management refer to these IFAS documents, or contact your local extension agent for additional information on this and any topic regarding your gardens and more.

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Joshua Criss

Josh is a UF/IFAS Extension Agent in Santa Rosa County Florida.He specializes in residential horticulture and is the coordinator of the Master Gardener program.In this capacity he is charged with assisting residents through research backed information with Florida Friendly lawns, landscaping, and gardens.He has worked in agriculture research, commercial greenhouses, and as a tree grafter.Passionate about learning, he enjoys applying ecological principles to help people create natural landscapes.