Cover Crops for Vegetable Gardens: What to Plant, When and How

Bare soil over winter erodes, loses nutrients and fills with winter weeds. Penn State Extension's advice to home gardeners is that "soil is meant to be covered," and a cover crop is the cheapest way to do it. Cover crops, sometimes called green manure, help reduce compaction, catch leftover nutrients, prevent erosion and, once they break down, add organic matter that builds soil structure. Legumes add nitrogen too. This guide covers which cover crop to choose, when and how to sow it, and how to get rid of it in spring without hurting your vegetables.

Choose by what you want

Ohio State Extension sorts garden cover crops into three groups:

• Grasses (cereal rye, oats, wheat, barley) build organic matter and soil tilth with their abundant roots.
• Legumes (clovers, peas, beans) add nitrogen for next year's crop. The amount depends on the species and how much it grows.
• Brassicas (radish, turnip, mustard) help break up compaction, especially the large radish types.

A mix gives you more than one benefit, and Ohio State suggests leftover brassica seed such as kale or radish as an easy way to start. If you're nervous about killing a cover crop in spring, begin with one that winterkills, such as oats or radish, which die over a cold winter and leave a mulch you can plant through.

Common garden cover crops

Planting times and germination temperatures are from Iowa State and Penn State Extension. Winter survival depends on your climate: a crop that usually winterkills can survive a mild winter, and one that survives in Ohio may not in Minnesota.

When to sow

Sow as early as you can after a bed empties, so the cover crop has time to establish before cold weather and short days stop it. Penn State's dates for the Mid-Atlantic and Northeast: brassicas such as radishes and turnips in August, clovers in August or September, oats until September, wheat until October and winter rye until about early November. Ohio State says most cover crops should be planted by the end of September, with wheat, cereal rye, rapeseed and kale possible through mid to late October. You don't have to plant everything at once; sow each bed as its summer crop comes out.

In mild-winter areas, fall is also a main vegetable season, so a cover crop usually goes on beds you're resting rather than across the whole garden. Our what to plant in fall guide covers the vegetable side of the calendar.

How to sow a cover crop

1. Clear and rake. Remove spent plants, debris and large stones, and rake the bed smooth. Loosen hard soil so seed makes good contact.
2. Broadcast the seed. Penn State suggests about 4 pounds per 1,000 square feet for rye, wheat and oats, 1 to 2 pounds for annual ryegrass, clovers and alfalfa, and about 1 pound for brassicas. Iowa State gives home-garden rates in ounces per 100 square feet, about 2 to 3 ounces for rye, oats and wheat. Always check the rate on the seed bag.
3. Rake in lightly and water. Rake the seed in and water with a fine spray. Ohio State notes you can also sow in rows with a hoe.
4. Feed if needed. Penn State suggests a light application of a complete fertilizer to get the crop started, and a lower-nitrogen product for legumes.

Ending it in spring

Most overwintering cover crops start growing again in spring and must be killed before you plant. UMD says this usually happens in late April or early May. Penn State and UMD both stress cutting the cover crop before it goes to seed, or it becomes a weed. Iowa State notes that termination is most effective at about 50% flowering, usually a week after flowering starts. Options for a home garden:

• Let it winterkill. Oats, radish and field peas usually die over a cold winter; plant through or rake aside the residue.
• Mow or cut, then turn under. Penn State suggests turning winter rye under when it is 10 to 12 inches tall, or mowing it first if it is taller. Turn under at least 2 to 3 weeks before planting so it can break down.
• Smother it. Ohio State describes covering the crop with cardboard or a tarp as a no-dig option.
• Crimp cereal rye. Rye can be crimped flat with a sharp tool once it is in full flower, leaving a mulch to plant through. Timing has to be exact or it regrows or reseeds.
• Pull it. For small beds. It is the most work and removes much of the organic matter benefit.

Cover crops in raised beds and small gardens

• Pick easy-to-kill crops. In a raised bed, oats, field peas, crimson clover or radish are easier to manage by hand than a dense stand of cereal rye.
• Cut and leave it on top. In a no-dig bed, cut the crop at the soil line, leave it as a mulch and plant transplants through it.
• Fill summer gaps. Buckwheat is a fast summer cover between spring and fall crops; UMD lists it with white clover as spring or summer options. Cut it as soon as it flowers so it doesn't reseed.
• Think about wildlife and smell. Penn State notes that legumes such as clover can draw deer, and brassicas can smell like rotten eggs as they decompose.

Fitting cover crops into your rotation

A simple rhythm works for most gardens: spring crops, summer crops, then fall vegetables or a cover crop. UMD Extension suggests mapping all three rounds when you plan, and our succession planting guide shows how. A legume cover crop before a heavy feeder such as corn, tomatoes or squash is a common choice, and a rye bed is a good home for transplanted tomatoes or peppers the next spring.

Frequently asked questions

What is the best cover crop for a vegetable garden?

It depends on your goal. Cereal (winter) rye is the most cold-tolerant and builds organic matter, oats are easy because they winterkill, crimson clover and field peas add nitrogen, and radishes help loosen compacted soil. Mixes combine benefits.

When should I plant a cover crop in my garden?

In late summer or early fall, as beds empty. University of Maryland Extension gives a window of about mid-August to mid-October, and Penn State says winter rye can go in as late as early November.

Is it too late to plant a cover crop in October or November?

For most cover crops in cold-winter areas, yes by late October. Cereal rye is the exception: Penn State says it still germinates at about 35°F and can be sown until about early November.

How do I get rid of a cover crop in spring?

Cut or mow it before it sets seed, then turn it under or leave it as mulch at least 2 to 3 weeks before planting. Smothering with cardboard or a tarp also works, and crops such as oats and radish usually winterkill on their own.

Can I plant vegetables right after a cover crop?

Wait about 2 to 3 weeks after turning it under so it can break down. After cereal rye, small seeds such as lettuce and carrots may struggle for a few weeks, so use transplants or a different bed.

Can I use cover crops in raised beds?

Yes. Choose crops that are easy to cut by hand, such as oats, field peas, crimson clover or radish, and cut them at the soil line in spring, leaving the residue as mulch.