Brassica Cover Crops - Key Growing Information
Uses: Brassica species provide rapid growth in cool weather, produce abundant biomass, prevent erosion, alleviate compaction, and suppress weeds. They contain compounds that can offer disease and soilborne pest suppression. They are highly effective nutrient scavengers, though nitrogen can be lost before the next crop when winterkilled. Plant as part of an overwintering mix to retain nitrogen longer. Some species can be used for livestock and wildlife forage.
Culture: Do not plant before other Brassica crops as they harbor similar pest and disease issues. Sow ¼–1" deep, depending on seed size and variety. Seed can be drilled using a grain drill or broadcast and covered lightly. Brassicas prefer cool weather, so spring or late summer sowings are most productive. Radish and turnips are best planted in fall to prevent premature bolting and to encourage root elongation/fill.
Soil Requirements: Most brassicas prefer a pH of 5.5–8.5 and well-drained, fertile soil. Soil temperature for effective germination should be between 45–85°F (7–29°C).
Seeding Rate: When broadcasting, seed at the higher end of the stated range. Mustard: ¼ lb./1,000 sq.ft.; 5–15 lb/acre. Oilseed Radish: ½ lb./1,000 sq.ft.; 10–20 lb./acre. Turnips: ¼ lb./1,000 sq.ft.; 5–8 lb./acre.
Grazing (Forage Turnips and Oilseed Radish): Begin grazing when roots reach 2–4" diameter and continue throughout the winter.
Harvest (Oilseed Radish): For oil production, harvest tops of plant after seed has matured. Incorporate the root into the soil.
Termination: Brassicas can be effectively terminated by mowing or tilling when flowering. To capture biofumigant benefits, mow at flowering and immediately till or tarp. Radish and turnip roots are easiest to manage when they are allowed to break down overwinter. Brassicas will winterkill reliably in Zone 6 and colder. Turnip roots can survive temperatures down to 10°F (-12°C).