Plant These Cover Crops to Improve the Soil in Your Raised Beds Over Winter

Every growing season, the soil in your raised beds loses nutrients and structure. Planting cover crops and then allowing those plants to hang out in your garden all winter is a simple way to add organic matter to your garden without using fertilizers. It also can improve the structure of your soil and more.

Think of it as doing a crop rotation between your fall and spring gardens, only you're planting these crops with the aim of improving the health of your overall garden, not for production.

I personally don't plant cover crops in my raised-bed kitchen garden for two reasons. One, I'm still growing and harvesting my favorite leafy greens and frost-tolerant veggies in my raised beds in late fall, when it would be time for me to plant cover crops for the winter. Two, cover crops have a tendency to spread and take over your raised beds (that's kind of the whole point, right?), but I like to leave some plants to overwinter in my garden. It's rare I would pull biennials like kale and Swiss chard or perennial herbs from my raised beds for winter.

That being said, many of you having been asking about cover crop plants for winter, so here ya go!

5 Reasons to Plant a Winter Cover Crop for Raised Beds

Cover crops have numerous advantages for the overall health of your garden, particularly the soil in your raised garden beds.

Cover Crops Help You Avoid Using Mulch

I'm not a big fan of mulch. I've found it just gives pests a nice little place to hide. I'd much rather use compost or some of type of living mulch, aka cover crops.

Cover Crops Suppress Weeds

If you don't plant something in your garden, nature will put plants there for you, but they probably won't be plants you enjoy looking at or want to eat. It's always better when you, the gardener, get to decide what plants are growing in your space.

Some cover crops are actually allelopathic, which means they release toxins that prevent weed seeds from germinating. Even after these plants die, they continue to release toxins through their decomposing leaves and roots. Don't worry—by the time you'd like to plant in the spring, your well-draining soil should have moved these toxins below the root zone of your new plants.

Cover Crops Retain Moisture

Bare soil dries out much faster than soil that's covered in plant mass. And dry soil loses a lot of nutrients. We want to keep those nutrients in the soil so that we don't have to completely amend our beds in the spring. We can just add some compost to the soil surface and be ready to plant.

Cover Crops Aerate the Soil

Popular cover crops options have sturdy roots that break up compacted soil and add lots of little air pockets.

Cover Crops Add Organic Matter to the Soil

The roots of your cover crop can stay in the soil and will add nutrients as they break down over time. When you chop and drop the leaves and stems of these plants, they turn into green manure that will feed and nurture your soil.

What Qualities Do We Look for in Good Cover Crops?

There are basically four qualities that make plants good candidates to be cover crops in our vegetable gardens. Plants should be fast-growing, low-maintenance, and easy to terminate (or remove). These should not be plants that you have to tend on a weekly basis.

Cover crops should also improve the garden soil in some way, either by adding nutrients the way peas fix nitrogen into the soil or by breaking up compacted soil the way the large roots of something like a daikon radish can.

Cover crops typically aren't chosen for their edible plant parts, though many do produce edible parts if they're given the ideal conditions. Thanks to their quick and easy nature, lots of the cover crops that are recommended for raised beds actually make great microgreens and sprouts, as well (think radishes, alfalfa, buckwheat, and peas).

When Do You Plant Cover Crops for Winter?

The best time to plant cover crops in your raised bed for winter is about one month before your first frost date. If you treat your frost dates like bookends on your growing seasons, then you basically use cover crops to fill all that empty space until you're ready to start gardening again in the spring.

Since the soil in your raised beds stays warmer for longer than the soil in the ground, you might be able to push your planting a bit later. Basically, as long as your soil is workable (meaning the top 3 to 4 inches of soil can be dug into), you can plant cold-tolerant cover crops. The goal is for your cover crops to germinate and grow but not have time to reach maturity before wintertime. The reason you don't want them to grow to maturity is because they'd start taking nutrients from the soil instead of adding.

Some cover crop varieties will be killed off by winter weather, and others will go dormant. Either way, they'll remain in the soil over winter to protect it from erosion.

What cover crop can you plant in December?

If your soil is still workable and your temps are in the 40s or higher, you can plant frost-hardy crops like winter rye, peas, and lentils.

Types of Cover Crops for Raised Beds

Most of the cover crops that are recommended for raised beds fall into four different categories: brassicas, legumes, broadleaf plants, and grasses. Let's look at some of the best cover crops, starting with our brassicas.

Cover Crops from the Brassica Family

Plant brassicas if you're looking for soil aeration and a tasty harvest or two.

Radish as a Cover Crop

The two most popular types of radishes to use as cover crops are daikon radishes and oilseed radishes. Oilseed radishes have thinner roots than daikons and grow a bit faster. Unlike daikons, they're not typically grown with root harvests in mind. They make for a great cover crop because their large taproots break up compacted soil and their large leaves shield the soil surface. Daikon radishes are ideal if you'd like to potentially harvest roots at the end of winter. Their supersized taproots are also particularly good at aerating soil. Don't forget that radish greens are edible.

Mustard as a Cover Crop

Mustard plants with their large leaves make a wonderful cover crop for raised beds. They're frost tolerant, so you can get some leaves to fill your salad bowl before a hard frost hits. Like radishes, mustards also have pretty tough taproots, but theirs dig deep instead of plumping up. Either way, it's great for the structure of your soil.

Cover Crops from the Legume Family

Members of the pea family fix nitrogen into the soil, so they're especially great to plant if you've grown something like corn in your raised beds that might have depleted nitrogen in the soil. This group is also super fast-growing if you're looking for a cover crop that will sprout and grow within a week or so.

Alfalfa as a Cover Crop

Alfalfa is a popular cover crop for farmers to use in their fields, but it works in raised beds, too. Alfalfa is actually a perennial, so if you were to just leave it be, it'll eventually produce beautiful purple/blue flowers that are beloved by pollinators.

Peas as a Cover Crop

Peas and fava beans are wonderful cool season crops. In fact, I'm often growing them in my garden well into the late fall and early winter months, but I grow them up a sturdy trellis for beauty and production. If you're using peas as cover, you'll let them sprawl over your beds. These are frost-hardy plants, so you have the added bonus of harvesting some pea shoots for your next stir fry!

Similar to peas are lentils, another cold-tolerant cover crop option. They can germinate in temps as low as 40°F and will provide ground cover all winter long.

Clover as a Cover Crop

Did you know those pretty little clovers popping up in your yard are related to peas and beans? Clover will fill in your garden within the first few weeks of planting thanks to its fast germination and spreading growth habit. Even though many people consider clover a weed, it makes for an excellent weed suppresser in your garden. Popular clover options include white clover (also called Dutch clover), crimson clover, and red clover. If you leave clover in your beds for the spring, you'll have beautiful blooms for the pollinators. Some gardeners swear by using clover to deter cabbage worms, which would be a definite win.

Hairy Vetch as a Cover Crop

It might not sound like something you want anywhere near your garden, but hairy vetch is actually a winter-hardy cover crop that's great at improving sandy soils and retaining moisture. It has a spreading growth habit like its clover cousins and produces pretty purple flowers in the spring.

Broadleaf Cover Crops

Buckwheat as a Cover Crop

Buckwheat makes an excellent cover crop. It germinates and grows quickly, suppresses weeds with its allelopathic effect, and breaks down quickly into organic matter. If you were to let it grow to maturity, you could harvest the seeds to make flour, but the leaves of buckwheat are also edible. Buckwheat will die after your first frost, but you can just leave the plants in your garden as living mulch.

Cover Crops from the Grass Family

The most widely used cover crops come from the grass family. Grasses have extensive root systems that add a lot of organic matter to the soil and protect it from the elements.

Winter Rye as a Cover Crop

As its name suggests, winter rye, a type of cereal rye, doesn't mind cold weather and can be planted later than most of these other crops. Rye has fibrous roots that loosen compacted soil and provide lots of biomass to break down later. Depending on where you live, this frost-hardy plant might continue its growth all winter long. If that's the case, you'll want to chop and drop it a couple months before spring planting so that the toxins from this allelopathic plant have time to disperse.

Oats as a Cover Crop

Like rye, oats can survive over winter in many areas. Oats are great at recycling nutrients in the soil and protecting soil from erosion, making them particularly desirable as a winter garden cover.

Sorghum as a Cover Crop

Also called sudangrass, sorghum will die back after frost and become living mulch if left in place.

Barley as a Cover Crop

Barley can grow throughout the winter months in warmer climates. It's typically mowed down to create a wonderful living mulch.

Winter Wheat as a Cover Crop

This is another popular plant for farmers to use as a cover crop. Winter wheat sprouts and grows quickly in the fall and then dies back in winter.

How to Plant and Grow Cover Crops

Follow these five simple steps to plant and grow your cover crop of choice in your raised beds:

Step One: Clear the Raised Bed

Remove any existing plants in the raised bed by cutting them at their base.

Step Two: Broadcast the Seeds

You won't be growing these plants to their full potential, so you really don't need to worry about spacing them out. Just scatter seeds evenly over the soil surface and sprinkle some soil or compost over them.

Step Three: Water

Keep your raised beds well watered while you're waiting on your cover crop to germinate. Once plants are growing, you can cut back to one deep water a week during dry spells. You won't need to water winter crops at all once they're receiving snow.

Step Four: Let Them Do Their Thing

You can basically forget about your cover crops as they die or go dormant until the spring.

Step Five: Chop and Drop

Cut all the plants in your raised beds at the base about 4 weeks before your spring planting if you want the plant matter to decompose in your beds. Otherwise, remove all plant materials and toss them in your compost pile.

Time to Plant Some Winter Cover Crops

I hope this gave you a better idea of the cover crop possibilities during your coldest months of the year.

Thanks for being here and helping to make gardening ordinary!