I have two raised garden beds (8 x 12 feet) in my back yard. Recently I read somewhere that having a cover crop during our wet winter months would help decrease the leaching of nutrients and would also help bind nitrogen in the soil.
Three suggested cover crops were crimson clover, Australian field peas (did they mean Austrian winter peas?), and vetch.
What would you suggest? Are these good recommendations? Which
might be the best?
Sustainable Horticulture: Today and Tomorrow (R. Poincelot, 2004, p.
372-377), says,
“Cover crops, when managed as green manures, can supply considerable nitrogen
for [vegetable] crops.”
Legumes, like the pea and vetch you mentioned are
good choices for increasing the nitrogen level in soils. (Hairy vetch, Vicia
villosa, and Austrian winter pea, Pisum arvense). Crimson clover (Trifolium
incarnatum) is almost as efficient at supplying nitrogen to the soil.
Hairy Vetch supplies 33-145 lb of nitrogen per acre/year to soil, Austrian
winter pea supplies 53-100 lb/acre/year, and Crimson clover supplies 19-114
lb/acre/year.
Another species you might consider as a cover crop is Fava bean (Vicia
faba), which supplies 25-105 lb/acre/year.
Additional information about growing cover crops in the Pacific Northwest
can be found on this information sheet from the Washington State University extension.
Territorial Seed Company, in Oregon, sells small quantities of cover
crop seed by mail order, including Hairy vetch, Crimson Clover, and Fava
Bean.