5 Steps to Choosing Spring Cover Crops

Cover crops grow on trial farms all year, but spring looks different from other seasons, and from field to field depending on the rotation.

Medium Red Cloveris usually sown in spring, but it's also often undersown into knee-high corn to give winter cover that grows back the next spring.

Elsewhere you might find winter rye and hairy vetch coming up through a protective mat of winter-killed field pea, crimson clover and ryegrass, all part of our Fall Green Manure Mix.

Corn undersown with medium red clover

More on medium red clover…

Used well, these and other covers help growers and gardeners improve tilth, feed soil life, fix nitrogen, catch and hold nutrients, ease compaction, smother weeds and more. Your own results will depend on your situation.

But in any region, field or season, a cover crop won't deliver those benefits without good planning and care. A badly managed cover crop can actually do more harm than good.

Here are the main things to think about when planning your spring cover crops.

Spring green manure mix

Cover crops can do many jobs, and one planting often does several at once.

Spring green manure mix:

• Covers the soil early in the season
• Builds soil organic matter
• Smothers weeds coming up through a winter-killed cover or on ground left bare over winter

More on spring green manure mix…

With so many possible benefits, what do you most want from a cover crop this spring and summer? Weed control? Part of a cash crop's nitrogen?

Of all the things a cover crop can do, aim for just a few with each planting. Every variety and mix has its own strengths and limits, so choose based on the result you want.

Our Spring Green Manure Mix, for example, combines field peas, oats and hairy vetch to help control weeds, fix nitrogen and add organic matter. Fast oats get ahead of weeds, while sprawling peas and vetch close the canopy, shading out weeds and keeping weed seeds from sprouting. Peas and vetch are both legumes, so they can turn nitrogen from the air into a form crops can use.

When the mix is ended and worked into the soil, its nitrogen and other nutrients are released for the next crop, your cash crop, and can cut how much fertilizer you need.

Spring wheat and clover

More on the benefits of grass and legume mixes…

When will you sow the cover crop, and when will you end it? Timing should weigh heavily in choosing the right option. Many cover crops can be sown at several times of year, but they often do different jobs depending on when they go in.

Oats sown in spring, for example, oats make a great fast green manure to work in before a main-season crop. Sown in late summer, they hold the soil over winter, and the winter-killed stubble leaves a thick mulch into early spring.

Say you're planning early spinach and then late-summer onions to overwinter. Your cover crop window is then early July to mid-August, not spring. Depending on your goals, buckwheat could be ideal for a short midseason gap. It's a fast, heat-loving green manure with lots of nectar for bees and other beneficial insects. (Tip: buckwheat's nectar flow is usually heaviest in the morning, so keep that in mind if you grow it for honey or beneficial insects.) Its broad leaves also close the canopy fast to help hold weeds back.

Many growers plant an early cover to fix nitrogen, control early weeds and add organic matter before fall crops such as squash, pumpkins, carrots and brassicas. Here again the Spring Green Manure Mix is a great early choice. Of its field peas, oats and hairy vetch, oats sprout first, in soil as cool as about 38°F (3.3°C). As the soil warms, the peas come up, then the vetch. Inoculating the seed at planting with a garden combination inoculant or a pea, vetch and lentil inoculant helps the pea and vetch roots form nitrogen-fixing nodules that enrich the soil.

Mowing the spring green manure mix

The same field shown in early spring at the top of this article, being mowed in early July.

Planting, managing and ending a cover crop efficiently takes the right equipment in good shape. Talk with nearby growers, tap the knowledge at your local Cooperative Extension Service, and make use of workshops and other resources. Keep a regular maintenance schedule that leaves time for repairs. Planning ahead lets you budget well and get your spring crop in when conditions are right.

Know which varieties do and don't do well in your area.

Many clovers, for example, struggle in dry climates. Red clover, crimson clover, and white clover do best in the eastern half of the U.S. and along the Pacific coast.

Sudangrass, by contrast, loves heat, handles drought and does well everywhere except the coolest, wettest areas.

On wet, heavy soils, oats tolerate conditions better than many covers and make a good quick early choice.

Other covers need different planting times in different regions to do their best.

In the Southeast, sweet clover is grown as a fall-sown biennial, while in most other regions it's sown in springand flowers the next summer.

One December, a customer called us for a cover crop recommendation. We asked where they farmed, how long their window was and what they wanted the cover to do.

Goals: Erosion control, green manure, fast growth.

Window: 40–50 days, sown in early spring and ended early to midseason.

Location: Tennessee, Zone 7.

Several of our cover crops fit this grower's needs. Based on their answers, here's what we suggested and why:

• Hairy vetch can go in early in spring, serve as a green manure and hold the soil, and as a legume it also fixes nitrogen.
• Barley is another good pick. It can be sown in soil as cool as about 38°F (3.3°C), grows very fast, holds soil and makes a good green manure.
• Oats are another good, fairly quick spring option that would meet the grower's goals.
• Sowing several cover crops together instead of one often gives better erosion control and weed suppression. If the soil has warmed enough at planting, our Spring Green Manure Mix would work very well here too.
• Other possibilities include buckwheat (again, if the soil is warm enough), ryegrass, and crimson clover.

Choosing the right spring cover cropmeans weighing your cover-cropping goals, your timing, equipment and upkeep, and your growing region. With clear goals, good timing and varieties suited to your region, you can put together a spring cover crop plan that does what you need this season.

These resources offer more help with spring cover crop planning.

Farm seed and cover crop comparison chart • PDF

Compare key traits and features at a glance with this chart.

• Top 10 uses and benefits of farm seed • Charticle
• Farm seed and cover crop comparison chart • PDF
• Early spring cover crops • Cornell CALS
• Cover crops and green manures • New England Vegetable Management Guide, UMass
• Cover crops for the Intermountain West • USDA NRCS, Boise
• Cover crops for home gardens• Oregon State University Extension
• Home garden cover crops west of the Cascades • WSU Extension fact sheet FS111E
• Managing cover crops in spring • University of Minnesota Extension
• Cover crops and green manures overview • ATTRA
• Cover crops for weed control in organic vegetables • American Vegetable Grower