Features: Now's the time to plant cover crops

(This article is dedicated to Claudia Temple, a WSU Master Gardener who passed away on Sept. 13 at the age of 51. She will be missed.)

Within the past week, fall has arrived. Leaves are beginning to turn, apples and pears abound in the markets and the days have a crispness about them, in contrast to the lazy warmth of August.

While there is still plenty growing in the fall garden, now is the time to be planning for winter and thinking about how to cover your garden soil.

Cover crops planted in the fall are an inexpensive way to build better soil for gardening. Cover crops, also known as green manure crops, are grains, grasses and/or legumes that will grow during fall and winter and that you can plow, spade or till under in the spring. Cover crops provide many benefits in gardens and agriculture, including protecting the soil from runoff and erosion, recycling and supplying nutrients, protecting water quality and suppressing weeds.

Common cover crops grown in this area belong to one of these three groups: grains and grass, legumes, other broad-leaved plants. Cereal rye is the most common grain used for cover crops in the Northwest. It provides good winter growth under cool conditions and produces a lot of biomass. Cereal rye seed is easily found through a farm and feed store like Skagit Valley Farmers Supply and it can be planted until late October.

Legumes are an important ingredient in cover crops since they have the ability to fix nitrogen from the atmosphere into the plant. Legumes fix nitrogen in association with bacteria called Rhizobia, which form nodules on legume roots. When the legumes are turned under and decompose, the fixed nitrogen is released for future crops. Unfortunately for us on the San Juan Islands, legumes tend to grow slowly in cool weather and most legumes are not well suited to wet soils. Nonetheless, legumes such as common vetch, Austrian winter peas, and fava beans do well as cover crops here.

Broadleaf plants such as mustard, rape and turnip can be used in small quantities as part of a cover crop. They need to be planted early, usually by late August.

How to plant

Cover crops need a good seedbed just like garden crops. After harvesting your garden crops, turn the soil and rake it smooth. Small seeded crops need the smoothest seedbed. Most of the common cover crops (cereals, vetches, Austrian winter pea, fava bean, and buckwheat) have medium to large seeds.

You can plant seeds either by broadcasting cross the area or using a garden planter that places seeds in rows. Cover the seeds by raking at least 1/4” deep or rototill no more than 2” deep. This provides good soil-seed contact and protection from drying, which increases germination.

Cover crops planted in established gardens do not need to be fertilized. Enough nutrients will remain available in the garden to meet their needs. Summer and early fall plantings usually need irrigation to germinate and become established.

You can plant cover crops by section in your garden, planting the earliest cover crops as soon as harvest is complete in the earliest parts of your garden. Many gardeners are still harvesting some parts of their garden into November or December. Since this is too late for planting cover crops, these parts of the garden are better mulched with straw or compost. If enough space is available, gardeners can plant cover crops between rows of late crops.

Comment on this story.

COMMENTING RULES: We encourage an open exchange of ideas in our online community, but we ask you to follow our guidelines for respecting community standards. In a nutshell, don't say anything you wouldn't want your mother to read.