Raised beds are a common way to grow edible and floral plants when either space is limited, bending down to the surface of the native soil is a challenge, when the present soil is not healthy/ compacted or non-existent (ex. concrete), or used for simply aesthetic purposes (window boxes). For more information, see HGIC 1257, Raised Beds
Figure 1. Cover crops grown in 4 x 8’ rectangle raised beds (a-c) and a 4 x 4 x 4’ triangle raised beds (d-f). Cover crops were planted early October 2020. Note that a dense cover developed by 09 November 2020. Cover crops planted were: (a and d) winter pea, (b and e) a mix of crimson clover, hairy vetch, daikon radish, cereal rye, and winter pea, and (c and f) cereal rye. Certain covers died back due to freezing temperatures by 12 December 2020, with cereal rye the only cover still alive on 25 January 2021 (f).
Photo credit: Sondra Sexton
What should you do with raised beds in the winter after the edible and floral fall crops are done, or for those couple months between summer and fall plantings? Plant cover crops, of course! Cover crops help fulfill many important niches for increasing the health of the soil:
- Cover cropping keeps live roots in the ground during a time of the year that usually does not have any: The soil microbes that turn organic matter into nutrients prefer to live on and or very close to living roots. Cover crop roots provide a “home” for microbes when raised beds are not used for edible or floral plants.
- Cover crops increase plant diversity which favors microbial diversity: Cover crops diversify food sources for soil microbes. In return, a more biodiverse microbial community results in nutrients, energy, and water cycling for the next growing season’s crops and assists with keeping unwelcomed microbes (like pathogens) in check and not becoming a potential problem.
- Cover crops keep the soil in the raised bed covered: Soils covered by living cover crops and cover crop residues help mediate soil temperatures, moisture and provide habitat for many other soil organisms (earthworms, insects, and microbes). As residues decompose, they also contribute to the next crop’s nutrient, energy, and water demands. Residues also help with weed control during the growing season. For mounded raised beds, cover crops (live and their residues) also intercept raindrops. Intercepting raindrops results in more water moving into the soil and not dislodging soil, causing soil erosion of the mounds.
No space is too small for utilizing cover crops. Cover crops can be used in mounded beds, walled-off raised beds, raised beds on stands, and even window boxes!
Keys to cover crop success in raised beds:
- Plan ahead: Make sure the cover crop(s) you choose will not host specific pathogens or insects that are problematic for the edible and or floral plants to be planted during the primary growing season. Match the cover crop(s) with the season(s) that the raised beds are not used for edible and floral plants. Match the cover crop(s) with the needed niche (ex. alleviate compaction, fertility, increase organic matter, water retention, etc.).
- Terminate the cover crop(s) at the right time: most cover crops should be terminated when they are at 50-80% bloom. Do not allow the cover crop(s) to go to seed, or else they may germinate and compete with the edible and floral plants during the desired growing season. If it is getting close to planting the crop for the growing season, but there are no flowers on the cover crop(s), that is OK! Go ahead and terminate them anyway.
- Termination of the cover crop will depend on the size of the raised bed. For small-medium raised beds, cut the cover crops using shears at the base of the plant. For larger raised beds, use a weed-wacker. Evenly place all of the plant cuttings on the soil surface. There is no need to cut the cover crop(s) into small pieces. Simply laying them over the soil surface will suffice.
- Planting time! When it is time to seed or plant edible and floral seedlings, move the cover crop residue to the side, leaving enough space to seed/plant (~ 1-2 inch width). Do not disturb the residues. Over time, as the garden grows, the residues will break down and contribute to that cycling process.
Gardeners will be most interested in fall cover crops for their raised beds. Cover Crops for the Fall is a good place to start. Navigate to the Southern Cover Crop Resource Guide to learn more about different cover crops to plant for which season, and use the individual cover crop information sheets to learn more about main benefits and concerns, seeding rates, when to plant and terminate, and other information. This website is a work in progress, so please select the “mountains” region for “coastal” until the coastal section is populated. For the most part, the information is the same, except that planting dates are two weeks earlier and termination dates are two weeks later for the coastal region. Many raised bed gardeners may also be interested in using cover crops in their raised beds for wildlife benefits (ex. For pollinators and birds). Navigate to Integrating Cover Crops for Ecosystem Services to learn about which cover crops promote certain wildlife.
Want to learn more about soil health? Navigate to the USDA Natural Resources Conservation Service Soil Health Management webpage.
