Cover cropping is a soil amendment system we use to improve the soil’s structure and overall fertility. Put simply, we cover crop by growing masses of plants in our beds toward autumn, allowing them to overwinter, and incorporating their decayed foliage and roots into the soil in the following spring as green manure.
Traditionally synonymous with organic farming, cover cropping is absolutely a practice we can adopt in our own backyards, even in raised beds that are just a few feet long! By selecting the proper cover crops for your space and timing the seeding right, a wealth of benefits (all given by nature herself!) await.
Reasons for using cover crops are many:
- – Cover crops have the ability to break up hardpan soil with incredibly strong root systems (alfalfa, mustard, daikon radish, rapeseed);
- – As cover crops decompose over winter, foliage and root systems feed a diverse variety of microbes and the thick layer atop the soil surface shields the harsh cold;
- – Root systems experience cycles of growth and decay, leaving behind a plethora of rich humus deep underground (and extra humus and organic matter means the soil has the ability to hold way more moisture! This is imperative in areas of drought).
- – Legume cover crops (clover, field peas, vetch) fix nitrogen from the air and deliver it to their roots in small nodules, replacing nitrogen that was used up during the growing season;
- – As they are incorporated back into the soil in the spring as Green Manure, decomposed cover crops add tons of organic matter to the top layers of soil, along with tons of food for Soil Food Web organisms.
Here are 4 steps to cover cropping your backyard garden, no matter if you have one raised bed or an entire acre of land:
1. Choose Your Cover Crop Varieties
- Similar to planting polycultures, the more variety of cover crops we plant, the more variety of microbes we will feed. Each cover crop secretes their own concoction of sugars in the soil. My method for choosing cover crops is simple: Choose 3-4 different types of cover crops, mix them up together in a bag, and sow them together.
To address multiple issues, I recommend choosing one cover crop from each category:
- Break Up Hardpan Soil: Alfalfa, Mustard, Daikon Radish, Rapeseed
- Fix Nitrogen: Crimson Clover, White Clover, Field Peas, Common Vetch, or any leftover bean seed
- Add Carbon to Balance Nitrogen: Ryegrass, Annual Fescue, Winter Rye
One More Tip: Essentially anything can be a cover crop. So if you have an excess of any type of seed, feel free to try using that – just make sure you have 3-4 different types of seeds in the mix with one legume. This Cover Crop Growing Guide is useful and explains a ton of options – as long as you pick a few different ones, they will serve their purpose in your garden. Have fun with it!
2. Seed Your Cover Crops at the Right Time
When you seed your cover crops, you will do so toward the end of the growing season. In the Midwest, the time to seed cover crops is Early September-ish – but make sure to check your frost dates and germination times of your cover crops. Johnny’s has really great info on each seed’s page. No matter what growing zone you live in, you want your cover crops to be planted early enough so you get a good amount of green growth before your frost – about 12-18″ in height. This will allow the crops to grow enough of a root system, and enough green foliage to cover the soil without going to seed. If you think your cover crops will go to seed before the frost, simply cut them down, but be sure to leave all that good green stuff right where it is.
Seeding cover crops 1.5-2 months before the end of your season means most of your vegetable plants will still be growing. Some might even be thriving, and this is quite alright! Simply sow your cover crops around your existing plants. Some seeds may not germinate if the sunlight is blocked, but that’s okay. Even a little bit will make a difference in your garden.
If you have a large garden and plan to leave a few beds fallow during the growing season, consider cover cropping them starting in the spring. You can do this by sowing a round of cover crops in the spring, chopping them down before they go to seed, and then sowing another round of different crops afterward. Do not remove any of the plant material between seedings.
3. Shut Your Garden Down Leaving Cover Crops Untouched
- The cold has arrived and you’ve decided to clear your garden of your frost-bitten vegetable plants. Most people approach this by pulling all of the plants out by their roots, but I encourage you to not do this. Rather than pulling them entirely out, do the Chop ‘n Drop, which leaves root systems entirely in tact.
- By electing to leave your veggie root systems in place, you have just provided your soil microbes food for the entire winter. The roots will also hold your soil in place and prevent erosion. For smaller green plants (such as lettuces, spinach and arugula), you should leave them entirely in the garden, dead foliage and all. Leaving them be will allow the plants to decompose over the winter into valuable organic matter. As for your surrounding cover crops: Treat them the same way. Do not pull them out or cut them at all – you have grown them for both the roots and the foliage so they should be left untouched to overwinter.
4. Incorporate Your Cover Crops During Spring Soil Prep
Fast forward through winter (brrr! boo! hiss!) and now it is spring and time to prepare your soil. So what do you do with all of this leftover plant matter in your garden? Your first instinct might be to rip it out and compost it – Stop right there! Rather than ripping them out, the point of cover cropping is to incorporate all of that awesome decayed plant stuff back into the soil.
To prep your soil with decayed cover crops, you will gently dig them in with a spade or, as I prefer, this fork. You absolutely will not use a tiller for soil prep – if you are unsure why, read my article on Part 1 of Building Healthy Soil and Increasing the Biodiversity of the Soil Food Web. Try to “twist” the cover crops down into the soil rather than flipping the soil over onto itself – flipping the soil over will expose soil microorganisms to the air and oxidize them. Gentleness is key here. Some of the leftover roots from the larger plants might need to be removed, but do so with care. Once you’ve pulled the large roots up, consider cutting them up with your pruners and adding the pieces back into the soil. Any leftover bits of decayed cover crops can be seeded and transplanted into, and then it should all be covered up with mulch once the seedlings are established.
Once you have nurtured your soil microbes and have restored your garden back to her original, biodiverse fertility, there is very little you will need to do in terms of yearly soil preparation. Disturbing the soil, needlessly aerating it year after year with machines – this is a finicky, unnecessary step to soil prep invented by humans. Good gardeners know this and live by this. If we take care of our microbes, they will take care of themselves and us.