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Once I pulled my garlic from its raised bed this summer, I hadn’t made plans to plant anything else in it. A few weeks later, I found myself with a giant raised bed full of weeds. Rather than pull them and allow more to make a home, I thought I’d plant a cover crop instead. So I headed to my local seed supplier, William Dam, which has a retail shop, to ask about the best cover crops for raised beds.

What are cover crops?

On a broader scale, cover crops are planted by farmers to revitalize and improve the soil structure in their fields between plantings. You might see the word tilth used in descriptions of cover crops. Soil tilth refers to the health of the soil. A variety of factors from aeration and soil composition to moisture content contribute to the health of your soil (or lack of).

Cover crop seeds are sown in your raised bed, and the plants are later turned into the soil. An added bonus? These fast-growing, shallow-rooted crops help to prevent weeds. Cover crops are also known as green manure or green crops, because you’re basically growing your own compost.

Planting cover crops for raised beds

How do you make this nutrient-rich compost? Fall is a great time to grow cover crops because your veggie-growing season is coming to an end, and the beds will be empty until spring. When you’re ready to plant your cover crop, pull all the existing plants and weeds out of the raised bed. Densely seed your raised bed in late summer or early fall. Be sure to read the seed packet for timing as some plant varieties need warmer weather to germinate than others. However you don’t want the plants to mature before the winter. Some cold-tolerant cover crop varieties can be planted up to a month before your first frost date.

I just sprinkled the seed mix that I chose from my hands, being sure to broadcast the seed evenly throughout the raised bed. I want the plants to grow close together to keep the weeds away!

Allow the cover crop plants to grow through the fall and forget about them until spring. Plants will grow until winter arrives. Some varieties will go dormant and others will be killed off by the winter weather. In the winter, plants help to provide cover for microorganisms to overwinter. In the early spring, if they’re perennial, the plants may provide nectar for early pollinators, depending on when you mow them.

You want to make sure you mow down your plants before the seed heads mature. In a raised bed, I will likely use my whippersnipper (edge trimmer) to cut the plants. You could also try using your lawnmower. Then, I’ll use a rake to lightly turn the plants into the soil. (I’ll add photos of this process in the spring of 2020.)

You want to give the plants a few weeks to decompose before sowing seeds or digging in transplants. I’ve seen recommendations range anywhere from two to four weeks, to four to six weeks. Consult the seed packet for this info.

Which cover crops should you plant in your raised beds?

There are a few options to consider when choosing cover crops for raised beds. Niki has planted buckwheat, fall rye, alfalfa, and white clover in hers.

My 50/50 pea and oat mix to add to my raised bed as a cover crop.

Peas and oats: At William Dam, it was recommended that I plant a pea and oat 50/50 mix. It’s listed as a “very effective nitrogen and biomass builder.” And that the oats will utilize available nitrogen, building soil structure and suppress weeds (which is what I need them to do), while the peas will fix nitrogen for the following crops (which I will plant next spring). I will allow the plants to die off over the winter and then till the plants into the soil in the spring.

This raised bed owner grew oats as a winter cover crop because they die over the winter in cold climates. Then in spring, she chopped them up in the bed with her mower and left the residues in place to serve as a mulch.

Buckwheat (pictured in main image): Not only is buckwheat fast growing, it also breaks down quickly. If you let it flower, it will attract pollinators and beneficial insects. Mow the plants within 10 days of blooming, or anytime before.

Winter rye: This is a fast-growing crop that doesn’t mind the cold. You can plant it later in the season than many other plants. It’s touted as a great soil builder that helps to loosen compacted soil.

Winter rye is touted as a great soil builder that helps to loosen compacted soil.

Clover: Clovers fall under the legume category with alfalfa, which is typically used in farmers’ fields. White Dutch clover is a popular cover crop choice because of the flowers, which will attract bees. Some gardeners are starting to use this in their lawns, as well. Clover also attracts beneficial ground beetles and helps to combat cabbage worms. Crimson clover has really pretty flowers and doesn’t mind a bit of shade. This might be a good choice for a couple of my raised beds that get more dappled shade from the expanding tree canopy than when I first placed them.

White Dutch clover is popular both as a cover crop and in lawns.

I will report back with images of my cover crop!

Check out these raised bed articles for more tips:

• • The best soil for a raised garden bed
  • DIY potting soil
  • A compost how-to guide
  • Planting a raised bed
  • The benefits of raised bed gardens

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