Domesticated in the region now known as Iran and Iraq, oats have traveled the world so thoroughly that they seem native almost everywhere, and in the vegetable garden their usefulness as a cover crop is second to almost none. Sown in fall, they germinate quickly and form a dense stand 2 to 4 feet tall that outcompetes weeds through sheer vigor, their roots binding soil and preventing erosion through the bare winter months. Full sun and well-drained soil of moderate fertility gives the best results, though oats tolerate a wider range of conditions than many other cover crops, including soils that are occasionally wetter.

The one consideration worth remembering is that oats release allelopathic chemicals into the soil as they die back, which can inhibit the germination of seeds sown too soon after. A three-week waiting period between the die-down of the oat cover and sowing vegetable or ornamental seeds lets those compounds degrade and avoids the problem entirely. Where soil nematodes are a concern, oats are a useful rotation choice, as they are not a host to several common species. The green flowers, while modest, do attract beneficial insects, and the grain itself supports birds and small mammals if left to mature. In an orchard or permaculture garden, a fall-sown oat cover crop may be one of the most useful decisions made all year.