When seeds are soaked in the bacterial inoculant, it kick-starts the fixing process, and helps plants to synthesize nitrogen into usable chemicals that fuel plants.
Nitrogen fixing makes legumes a good choice for improving nutrition in poor soils. They fit well into rotations after a light-feeding plant, and before heavy-feeding ones.
Legumes are both winter hardy and winter-killed. They create ample foliage that provides a green manure or mulch, resist erosion, condition soil, and suppress weed growth.
Our top legume picks for cover cropping are up next.
11. Alfalfa
A prominent cover and rotation crop, alfalfa (Medicago sativa) has surface roots as well as a deep, long taproot that greatly improves water infiltration and permeability, and reduces soil compaction.
Alfalfa is a premier nitrogen fixer, and it also balances soil nutrients as it cycles other important minerals such as magnesium, phosphorus, and potassium.
An herbaceous perennial, it produces a healthy biomass that dies back in the cold winter, providing mulch for the dormant roots and good erosion control.
Growth resumes in spring, and tilled plants are used as a green manure to add nutrients and improve soil structure.
Organic alfalfa seeds are available at True Leaf Market.
Read more about growing alfalfa here.
12. Crimson Clover
A robust cool-season grower, crimson clover (Trifolium incarnatum) is another herbaceous perennial with winter-killed foliage and new growth in spring.
Plants produce an abundant biomass that mulches roots over the winter, and provides excellent erosion control and weed suppression.
Clover fixes large amounts of nitrogen, and its long taproots are effective at breaking up hardpan and thick clay soils.
Flowering clover also attracts important pollinators like bees and butterflies.
Crimson clover seed is available at Botanical Interests.
13. Fava Beans
Fava beans (Vicia faba) are hardy annuals that grow in cool and warm seasons. They develop a lavish biomass that can easily be tilled or cut and composted.
Popularly used as a nitrogen fixer, the stout, upright plants work well with vining species such as field peas and hairy vetch for excellent weed suppression and erosion control.
Fava bean seed can be found at Botanical Interests.
Read more about growing fava beans here.
14. Field Peas
Fast-growing field peas (Pisum sativum) produce a considerable biomass that makes them suitable for spring or fall use.
When sown with rye or oats for support and structure, paired plantings provide good weed control and a thick winter-killed defense for effective erosion control.
Field peas fix moderate amounts of nitrogen, and tilled plants contribute residues that improve soil friability and add nutrients.
Find Austrian field peas at True Leaf Market.
15. Vetch
Did I save the best for last? Hairy vetch (Vicia villosa) is at the top of the list of nitrogen fixers, right next to alfalfa. It makes a popular selection for crop rotation in both conventional and organic farming, and in home gardens too.
Winter hardy, vetches are slow-growing plants. But once established, they form a lush canopy of foliage that improves water infiltration and retention, crowds out weeds, and provides excellent erosion control.
The tilled green manure residue helps condition the soil into a finer, healthier texture with improved aggregates.
Avoid planting other legumes right after vetch, as this can increase the chance of root rot, nematode infestation, and white mold in those plants, according to Thomas Bjorkman, Professor at the School of Integrative Plant Science, Cornell University.
Hairy vetch seeds are available at Botanical Interests.
Learn more about cover cropping with hairy vetch here.
Soil Improvement in Every Season
Providing multiple benefits, the brassicas, grains and grasses, and legumes we use as cover crops improve the soil in every season.
Use them for green manure before growing heavy feeders, as winter erosion control to protect your topsoil, as a general tonic to improve moisture levels and soil structure, and to suppress pests and weeds.
Most are fast-growing and all are easy to cultivate – and you’ll love how quickly your garden responds to their use!
Do you have any questions about the cover crops mentioned here? Drop us a line in the comments below.
And for more soil improvement know-how, check out these articles next:
Lorna Kring
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