When growing gardens, one of the most important parts of doing it sustainably is keeping the soil fertile. Of course, it’s best to avoid doing this chemically because that would not be good for our food or the environment, and in fact, it ultimately is not good for the soil either. Many organic gardeners opt to add compost and natural amendments every year. But, one of the great tricks of the trade, the one most likely overlooked, is growing winter cover crops.

While it may seem counter-intuitive to cultivate more stuff to keep soils full of nutrient, the fact is that cover crops work differently than harvested crops. They are grown as a gift back to our garden beds, something just for them because they so willingly feed our fruits and vegetables for the rest of the year. With that in mind, winter is the perfect time for doing this because, of course, most of the gardening we do happens from spring to fall.

So, how do cover crops work?

The Benefits of Growing Cover Crops

Cover crops come with a bounty of benefits. In fact, it makes so much sense to grow cover crops that it’s hard to understand why everyone who grows a garden doesn’t. Not only are cover crops low-maintenance, but they make life easier on both the gardener and the crops.

1. Cover crops improve soil fertility. Essentially, these are crops that we grow in the garden for the express purpose of cutting them down in place to add organic matter. Cover crops rival both manure and compost because they naturally nurtures microbes below the surface, too.
2. Cover crops improve soil texture. In addition to supporting microbial life, the roots of cover crops can help with loosening soil, breaking it up and/or gluing it together.
3. Cover crops prevent erosion. Firstly, having plants growing in the soil helps to ease the impact of both rain, which can compact the soil, as well as wind, which can whisk it away. Additionally, the roots hold the soil in place.
4. Cover crops improve moisture retention. Organic matter in soil helps to keep moisture around because it acts like a sponge. This makes gardens drought resistant, which means less watering.
5. Cover crops prevent weeds, diseases, and pests. Because cover crops provide a canopy over the soil, weeds are less likely to pop up. The active soil life that cover crops Support help to destroy pathogens, and cover crops provide habitat for predatory insects, as well as pollinators.

Source: waferboard/Flickr

Choosing the Right Kind of Plant

Cover crops, despite “crop” being in the title, are not plants we are growing to harvest for ourselves. They are plants grown specifically to improve the garden, so they have to have traits well-suited for this task. Some of these traits are:

• nitrogen-fixing nodules on the roots, a common characteristic of leguminous plants, such as clover, vetch, and alfalfa.
• drilling root structures, like with daikon radish, that helps to break up compacted soil and, when decomposing, create biological pathways for other roots.
• matting root structures, such as with wheat, which work well to prevent erosion and create crumby soil texture.

Often cover crop farmers will use a mix of these specialized plants to get multiple benefits from the cover crop combination.

Choosing the Right Time to Plant

In reality, anytime a garden isn’t growing food crops is a good time to have it in cover crops. For example, buckwheat is a famously fast-growing summer cover crop that gardeners will plant in for a quick, fertility-building turnaround between early spring gardens and fall plantings. But, winter is ideal for cover cropping because much of what we grow in the garden requires warmth.

In general, for a winter cover crop, it’s best to plant them in September (early autumn), but they can be planted even later in mild climates. This usually works out very well because that’s when the last vegetables come in from the summer garden. Cover crops can been started around the mature plants that are still producing or sown right after the final harvest.

Source: Wisconsin Department of Natural Resources

The Best Winter Cover Crops

The best winter cover crops are those that can tolerate cold temperatures, particularly the temperatures wherever they are being grown. In other words, when choosing a winter cover crop, consider your winter. Here are some classics:

• Field peas can withstand temperatures down to 10 degrees Fahrenheit.
• Fava beans create a lot of biomass and survive sub-zero temperatures.
• Clovers come in good variety, with some that can withstand minus 20 degrees.
• Oats are a good choice for wet soils and work down to 15 degrees.
• Barley survives down to zero and can deal with dry, even salty soil.
• Annual ryegrass is another sub-zero classic that absorbs excess nitrogen.

How to Plant Cover Crops

When planting cover crops, they are broadcasted densely, as one would do when planting grass. Then, they are typically cut down before they have a chance to go to seed. Some growers like to turn them into the soil, but no-till practitioners will simply cut them and allow organic material a couple of weeks to dry out into a layer of mulch.

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