Cover Crops in My Urban Vegetable Garden

Linda Cameron’s garden Photo by Laura Steiger

by Linda Cameron
About five years ago I changed the way I approached vegetable gardening, becoming a succession planter and a no-dig gardener. My urban garden is half an acre with many flower beds, a food forest and a large vegetable garden. My vegetable garden has 26 beds, averaging eight by four feet with permanent mulched pathways between the beds. I have always been an organic gardener using only barriers against pests and making lots of my own compost to fertilize the vegetable garden, supplementing with mushroom compost. Most of the soil is covered with mulch, compost or cover crops.

Recent research has shown how important it is not to disturb the soil and to keep it covered with plants that feed the microbial community in the soil. The traditional definition of a cover crop is a crop that enriches soil to subsequently grow a productive food crop. Normally this crop is tilled into the soil or cut down just as it flowers to ensure the plant dies and no seed is produced so that the nutrients stay in the green matter and are not stored in the seed. In addition to adding nutrients to the soil, cover crops give a place for beneficial animals to hide, add organic biomass, break up ground, deter pests, control weeds, keep moisture in the soil, add diversity, increase beneficial microorganisms in the soil, cool the soil resulting in less stressed vegetables.

My aim, however, is to have many of my cover crops also serve as food crops. Since I am a no-dig gardener, it is essential that a cover crop be an annual crop that is winter killed. I learned this lesson when I planted annual rye grass in September; by snowfall the grass was growing vigorously and when the snow went in the spring it looked just like it did when the snow covered it in the fall. The grass had to be dug out and composted to allow spring seeding. After that I was much more cautious about using traditional cover crops and realized that I needed to educate myself. I listened to Charles Dowding, No-Till Growers, and Huw Richards on You Tube and read books, especially Jessica Walliser’s book Plant Partners published in 2020 and Gabe Brown’s Dirt to Soil published in 2018. Cover crops that I have used: buckwheat and cow peas (both summer cover crops), oats, nasturtiums, radishes, and legumes that fix nitrogen such as crimson clover, red clover, subterranean clover, lentils and fenugreek. Cover crops that I eat: fennel, lettuce, endive, chicory, cilantro, pea shoots, mustards and spinach.

To explain how I use cover crops in my vegetable garden I will describe my last year’s garden planting of cover crops. Early in the year cover crops are used between vegetable rows or, between plants such as the brassicas. Some of the cover crops are started as seedlings in 2” soil blocks, ensuring they are the same size or larger than the vegetable crop. When cabbage, kohlrabi, kale and broccoli were planted early to mid May a crimson clover plant was planted between each seedling. When the cucumbers are seeded, usually early June or after the sugar snap peas are done, a row of radish seeds is planted next to the cucumbers to act as a trap crop for flea beetles and to deter the cucumber beetle.

If a vegetable crop matures early a second vegetable crop is planted; fall cabbages that were planted early July were also interplanted with crimson clover. Lettuce is started mid to late July and planted out two weeks after seeding, allowing several days for hardening off. On some of the harvested brassica beds, crimson clover was direct seeded at the end of July and grew until covered with snow. Come next spring, I will plant directly in the bed leaving the old clover on the ground. Of the clovers that I have tried I found crimson clover to be the best; the flower is pretty, and it is an annual that winter kills in our climate.

Cool weather cover crops lettuce, chicory and endive are seeded mid July in 2” soil blocks to be planted end of July. Spinach is seeded third week of August in 2” soil blocks and planted first week of September. I found spinach seedlings the best as there is poor germination of spinach in the August heat. I get at least three pickings of spinach before it is covered with snow. In early spring about 70% of the spinach plants survive producing early greens until removed for spring planting. When the spinach seedlings were planted in their beds, rows of spinach were alternated with direct seeding of either winter radish, oat-pea mixture or lentil-radish-fenugreek mixture. I was hoping to leave the seeded grow cover to be winter-killed but this year the mice and vole population was large; they burrowed along the row of the oat-pea mixture eating as they went. So eventually I removed the oat-pea growth to the compost leaving only the spinach and radish because I did not want to feed the mice and voles helping them to survive the winter. It seems mice and voles are not keen on spinach and brassicas.

In previous years I had no problem with fall seeding up to mid September of the oat-pea mix. Whenever a space opened in the fall garden, seeds were direct sown until mid September. After that time there is not enough light for the plants to grow to a reasonable size.

Another good cover crop for mid to late August seeding is cilantro, since it likes cool temperatures. In summer any cilantro plant that grows, especially in pathways, is allowed to flower and set seed, which is collected for microgreens in the winter.

When using cover crops it is important to be cautious as the vegetable crop is the main objective of the garden. One example is marigolds; they love the rich friable soil of the vegetable garden and tend to grow so well they will quickly take over the bed unless kept in check.

The No-Till Growers YouTube channel has several recommendations: the need for seeds to be covered for good cover crop seed-to-soil contact, a non-compacted soil, weeds removed, and know how you are going to kill or remove the cover crop before planting if you are using plants that are not winter killed. If using a cover crop that is not winter killed it is important to cut it down at the base or roll it down just as it flowers but has not gone to seed to ensure that it does not regrow. It is okay to plant seedlings directly after taking down the ground cover and pulling it aside. It is also important to consider the decomposition time of the ground cover before direct seeding; you need 2 to 4 weeks before direct seeding especially if tilling a cover crop into the soil. I use only plants that are winter killed because I do not have the space to allow a cover crop to use a bed most of the season. I plant all my cover crops the same as vegetables, either as seedlings, especially in the heat of the summer, or in covered soil, mostly mid-August to mid-September.

Another factor that needs to be considered is cover crop allelopathy. Many of the cover crops give off chemicals that inhibit growth, especially seed growth of other plants, including weeds. Some examples are oats, winter rye, clover, radish, alfalfa. From what I have read all clovers are allelopathic. I have not experienced any allelopathic effects on my food crops since I usually plant seedlings not seeds. For example if the bed was planted with crimson clover for fall, then winter killed, carrots could be direct seeded in the spring due to the long period of time that has passed since the clover was growing.

Overall, I believe that cover crops in my vegetable garden have improved my food harvest and make it more enjoyable to be in the garden, especially in late fall when the cold tolerant cover crops are still green.

Seed Sources:
Any packets of seeds that are getting old and have low germination rate great for overseeding in the fall.
Larger seed companies that supply larger package sizes as it is too expensive to use smaller packets of seeds as a cover crop.
Microgreen and sprout seed packages available at local plant nurseries.
Organic seeds from local grocery stores.

About the Author:
Linda’s love of plants started at a young age by collecting, identifying, drying and scrapbooking wildflowers. At University her undergraduate degree was in microbiology with a minor in botany. Linda has gardened at her present location in Winnipeg for 48 years, starting with a vegetable garden and gradually adding trees and shrubs, both ornamental and fruiting, and ornamental beds.

Published:  May 2022