Plantings before late September are susceptible to disease and premature death. Winter wheat covers the ground quickly in the fall, but does not grow as vigorously as rye does in the early spring, making it a good choice for late planted gardens. Wheat is more leafy than rye, so it may decompose faster when it is turned into the soil. Spring oats are a good choice for an early cover crop, as they grow vigorously when the soil is warm. Oats should be planted by early September in the Puget Sound area to get good fall growth.
Later planting is unlikely to produce good ground cover.
Planting can be as late as October in the Willamette Valley. Oats tolerate wet and heavy soils better than other cover crops, but oats are susceptible to early winterkill. Winterkill is less of a problem in the Willamette Valley. Spring barley is an early cover crop that is similar to oats in growth characteristics. It is also susceptible to disease and occasional winterkill.