Gardening Tips Week 22: Cover Crops

What to do this week

This is the time of year when you might be starting a new garden bed — maybe your first, maybe an extension of your existing garden — which makes it a good time to talk about cover crops.  As with crop rotation, which we discussed last week, cover crops are often incorrectly assumed to belong in the realm of agriculture, but they also have their place in urban gardens and other small operations.

Cover crops are really useful tools for the gardener, even the home gardener. They can bind nutrients, stop soil erosion and cover bare spots so you don’t get erosion and weed pressure. Different cover crops are good for different things: buckwheat, for example, doesn’t add a lot of organic matter to the soil, but is really good at shading out weeds with its broad leaves. Oats and other cover crops from the grain family are handy because they encourage things in the soil called vesicular-arbuscular mycorrhizae (VAM), fungi which help with nutrient uptake, particularly phosphorus.

Flowering buckwheat cover crop. (Source: The Campus Community Garden http://web.uvic.ca/~ccgarden/buckwheat-covercrop/, University of Victoria)

Flowering buckwheat cover crop. (Source: The Campus Community Garden, University of Victoria)

One good technique for small cover-crop use in a way that doesn’t disturb the soil but maintains its structure is to dig the soil a bit, roughly, then sow a crop of buckwheat right away. The buckwheat will shade out the weeds, rhizomes and quack grass, strangling them out. After the buckwheat starts to flower, you mow it down and sow another cover crop of oats. That will winter kill, and leave you a lovely garden bed for next year. Your patience will be rewarded. This is a way of opening up new ground for planting that not only doesn’t disturb the soil, it actually contributes to it.

You can use other things as cover crops. Some options are legumes, clover or alfalfa. I use forage kale because I get to eat it as well as benefit from it as a cover crop. Kale and brassicas in particular will break nematode cycles. With the brassicas, you have to be sure to mow them down before they flower or they will become weeds. This is also important with buckwheat. The extra work is worth the effort because they are very helpful for soil structure. Oilseed radish is very good for breaking up compacted soil. It sends a long taproot through the soil and will loosen it up for you.

Legumes are mycorrhizae neutral while brassicas discourage it. You may think you would want something that discourages mycorrhizae, and often you do, but if you have a problem with quack grass, a kale or other brassica cover crop rotation will really help because it will make the soil less receptive to that particular perennial weed.

It is worth repeating that you don’t want any cover crop to become a weed, so unless it is a crop that will die over winter, you have to mow it or cut it down in some way before it produces its own seed. Even that resulting organic matter can be a help. Leave it in place. What I do with my buckwheat-then-oats formula is that I scatter the oats when the buckwheat is grown, and then I mow the buckwheat down. The oats will sprout up through the cut buckwheat. Later, if you mow the oats when they are still green, they will break down very quickly and contribute further to your soil. Next spring you will just have to turn the soil over lightly, reducing the amount of tilling you must do. Eventually, you will find that you do have to do some digging, but the less tilling you do, the less you are disturbing your soil structure. If you sow the oats late enough and just leave them, they will die over winter. The mass on the ground will function as mulch, and protect the soil from winter erosion. Oats are not perennial, so you will not have an oat field to deal with in the spring.

Some people use winter rye for winter protection because it adds huge amounts of biomass, but you have to till it under in spring to kill it because it does not winter kill. With oats, they just die, but you do get less biomass. It is always important to think about what your particular bed needs, and pick a cover crop that meets those needs.

I started by talking about the use of cover crops to prepare new beds. In the city, it may be more common to cover the area with cardboard, keeping it moist all summer, inviting the worms to prepare your bed. That is a very useful technique, but as I have explained, you can achieve other objectives with cover crops while you are at it. You can contribute to soil structure by adding useful organic mass, or work against particular weeds. Nature will always fill an empty spot, so it is a good idea to avoid empty spots in your garden. If you don’t, nature will give you something that you might not want. Consider putting a cover crop in spots in your garden that you haven’t planted yet, or that are just getting left behind. That way you decide what is growing.

 

 

 

Market gardener, farmer, workshop leader, seed-saver, political candidate and mother, Michelle Smith has spent over 30 years coping with the challenges of our bioregion and in the process has built a store of practical and technical knowledge. The Inverness resident has served on the board of Seeds of Diversity Canada and represented Alternative Producers with the Federation of Agriculture but can do nothing about her hair. She is pictured with a head of Club Wheat, a seed that shares her approach to hairdressing.

 

 

 

Backyard food gardener Madeline Yakimchuk caught the food-security bug in the early ’90s through Cuba’s Urban Agriculture Department, taking her first permaculture course and planting her first garden. She can often be found discussing food security, nurturing a plant-based lifestyle or trying to give away vegetables. Professionally, she is GRYPHON media productions but sometimes uses la bruja in her volunteer work, most notably in managing the garden column, which begins life as a telephone interview.

 

 

 

 

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