This is the fifth in a series of blogs, about ancient soil amendments used in the garden. Each blog will discuss a common and specific type of soil amendment used in the garden, along with documentation for its use, as well as occasionally discussing why a particular soil amendment was chosen, or its relation to modern gardening practices. The original blogs, along with other gardening related blogs, can be found here.
A cover crop is exactly that – a crop which covers a field. Another term, green manure, is sometimes used when referring to cover crops, because the idea with a cover crop is that they will be turned back into the soil rather than being harvested. Living mulches must be made up of perennial plants, where as in general, cover crops are annuals.
Lupines are discussed at length as a cover crop. Here are two examples from Geoponika: “If the land is pervaded by roots you can sow lupines therein, cut them when they are in flower and plough it in so that the cut parts are turned under, and leave it after applying a thin layer of manure to it.” (GE 3-10.8). “Lupine has to be sown in exhausted soil, not needing manure, because it serves as fertilizer: in effect, it fertilizes whatever devitalized soil and makes it productive again.” (GE 2-3.9.6) Cato says of cover crops: “Crops which fertilize land: Lupines, beans, and vetch.”
These excerpts suggest that our ancient gardening ancestors knew without science what we now know – that lupines fix atmospheric nitrogen and use their taproots to reach down into lower layers of soil.
Though clover is a particularly popular cover crop, it is not the only one. The use of winter cover crops such as oats, barley and winter rye as a way to provide biomass and reduce soil erosion is frequently used in modern farming.
Legumes (like peas) and some brassicas (like radishes) are also common cover crops. Other cover crops noted by medieval authors include fava beans, oats, and hemp and later during the 14th century weeds became a cover crop (Zadocks, 2013).