Winter cover pair
Winter rye and hairy vetch, sown together in early fall to cover bare ground over winter and cut down in spring.
Why these are grouped
A rest for the soil. It benefits next season’s crop as a rotation break and green manure. The plants are not claimed to help each other while they grow.
Space it needs
At least 0.3 m²3 ft². If your bed is smaller, the planner grays this plant team out, says why, and offers the nearest adaptation that fits. It never swaps in something else without telling you.
What it looks like planted
- 8 × Cereal rye
- 1 × Hairy vetch
Between seasons
Nothing is left living in the bed over winter; the whole planting is re-established.
What it claims
The legume's residue mineralizes N for the next crop
How it works: A legume fixes atmospheric nitrogen into its tissue as it grows. When the crop is killed and its residue decomposes, soil microbes mineralize that organic nitrogen, converting a form plants can't use into one they can, and release it for the next crop. How much depends on how well the legume grew, and it is lower on sandy soils.
Evidence: checked against 2 sources in the research-based literature.
The 2 sources
Growing Cover Crops for Nitrogen on Vegetable Farms Penn State Extension
When cover crops are killed and begin to decompose, nitrogen can be released from the residues back into the soil where it can feed the next crop
Late Summer Planting Legumes to Produce Nitrogen Credits for Next Year Univ. of Wisconsin-Madison Extension (Crops & Soils)
The nitrogen credit depends on the amount of crop growth and when the legume was planted. Nitrogen credits are 50 lb N/a lower on sandy, coarse-textured soils.
The grain takes up the soil nitrogen the legume does not need, holding it against winter leaching
The grain's residue suppresses small-seeded weeds, and the next small-seeded sowing with them
How it works: Rye and sorghum roots and residue release allelochemicals (benzoxazinoids from rye, sorgoleone from sorghum) that persist in the surface soil for weeks after the cover is killed. A small seed sown into that layer has little reserve to push through the inhibition; a large seed or a transplant is already past the germination window.
Evidence: checked against 4 sources in the research-based literature.
The 4 sources
Cereal Rye Cover Crops, Allelopathy and Corn Iowa State Univ. Extension, Integrated Crop Management
Research has shown that susceptibility to allelochemicals is indirectly related to seed size - the smaller the seed the more susceptible the plant
Weed Management on Organic Farms NC State Extension
Small-seeded and slow germinating crops are more likely to be adversely effected by allelopathic cover crops than are large-seeded, rapidly germinating crops (Weston, 1996)
Organic Cool-Season Vegetable Crop Rotations for the Southeast Univ. of Georgia Cooperative Extension, Bulletin 1498
A direct-seeded crop with small seeds is particularly vulnerable to allelopathic chemicals
Cereal rye/winter rye: the perfect garden-reset cover crop Univ. of Illinois Extension
It needs to be terminated in mid to late spring before it goes to seed, about 2 weeks before the desired transplant date.
What to keep in mind
Two plants doing two jobs on ground that would otherwise sit bare. Rye is the grain that stands the winter; oats die back to a mat at the first hard frost, which is the swap for an early sowing or anywhere spring rye gets away from you. Crimson clover is the shorter legume that does not climb. Either swap gives up the climbing line, which only vetch on rye earns. Cut the rye at least two weeks before you sow anything small-seeded; the plan flags this for you. Hairy vetch is listed as invasive in Oregon and is weedy anywhere it sets seed, so cut it before it does. Buckwheat is the summer cover, grown on its own, and is not part of this pair.
Who does what, and the swaps
Each job in this planting can be done by more than one plant. The usual choice comes first, and each swap says what it costs.
Grain
- Usual choice: Cereal rye
- Swaps: Oats
Legume
- Usual choice: Hairy vetch
- Swaps: Crimson clover
What it costs the ground
Rotation history belongs to the ground itself, so this is what the planner records about this patch after the plant team comes out.
- Legumes: counts as a full season of this family
- Grasses: counts as a full season of this family
Where this plant team comes from
The grain-and-legume winter cover the extension cover-crop guides all describe (NC State 'Winter Annual Cover Crops'; UMass 'Cover Crop, Hairy Vetch'; Penn State 'Making the Most of Mixtures'; Clemson HGIC 'Cover Crops'; Univ. of Maryland 'Cover Crops for Gardens'), sown as a pair in early autumn and cut in spring.