The least expensive organic fertilizer in the world is – cover crops!
Cover crops for gardens are simply plants that are planted to cover your soil, especially during the off season.
And they can also be used during the growing season, interplanted with food crops or even in ornamental beds.
But they do much more than just cover the soil. Garden cover crops:
- Reduce nutrient leaching, increase fertility and increase organic matter without the added expense of bringing in fertilizers and organic matter,
- Control weeds and plant predators without every spraying a pesticide, as well as attracting beneficial insects and microbes without ever bringing in earthworms or ladybugs,
- Prevent erosion, break up compacted soil, improve both drainage and water retention, all without rototillers or compost or buying mulch
This is a small patch of clover and vetch I’ve let stay through the summer.
…And much more. Healthier soil, less work – what’s not to like?
The most common types of cover crops are legumes and grasses…
Legume Cover Crops
Legumes host nitrogen-fixing bacteria in their root nodules.
Fortunately, they contribute more nitrogen than they need for their own use, especially when they’re chopped down before going to seed.
Then their roots and leaves are allowed to decompose in the soil.
Some of the most popular overwintering legumes include vetch, various types of clover, fava beans, bird’s-food trefoil, cowpeas, and winter peas.
Which ones you use depends on your needs, but it’s most important just to pick one and roll with it.
Vetch has very high overall nitrogen production, while perennial white clover is a popular living mulch for use in orchards and ornamental gardens.
Red clover is often used as a dependable winter annual in eastern North America, while the tall and beautifully colored annual crimson clover is great for regenerating a fallow bed through summer in the west.
I’ve seen Austrian field peas, planted thickly in fall, completely displace persistent weeds in wildly overgrown beds. The peas sprout early in spring, shading the soil before the weeds have a chance to get going.
Grass Cover Crops
Grasses are great for creating lots of organic matter, controlling weeds, and reducing leaching of nitrogen and other nutrients.
They’re like chefs who can make a tasty and plentiful dish out of the leftover scraps.
They’re useful if your soil has a lot of nitrogen and other nutrients after harvest, because they’ll help prevent these nutrients from leaching away.
They also build humus effectively by growing fast and contributing cellulose and lignin.
Grasses are handy for their sheer exuberance – crowding out weeds with heaps of organic matter and by producing unfriendly root-zone “allelopathic” chemicals.
Because of those chemicals, it’s important to wait several weeks after removing the grass in spring before you seed vegetables.
High-carbon grasses take a lot longer than nitrogen-rich legumes to break down, though, so they may not be a great choice if your soil’s low in nitrogen, or if you need to plant in a hurry after turning in your garden cover crop.
The workhorses of winter cover crops for gardens are cereal rye and annual ryegrass. Oats can also be a good choice in areas with cold autumns and wet soil – they’re one of my favorites for my area.
Buckwheat, while not a true grass, is great for poor soils and for use in the shoulder season rather than over winter. And there are others, like barley, sorghum, and winter wheat.
Choosing Cover Crops For Gardens
I always try to mix a grass and legume – this is clover and oats (and garlic peaking through).
Among the many cover crops for gardens that are available, certain species and combinations are universally popular.
You’ll find that growers in your area may favor particular plants or grass-legume pairings, such as rye and vetch.
For home gardeners, the best way to select a cover crop is often to try a mix rather than choosing just one.
That way something should do well, whatever weather and soil conditions you have.
If you start with the basics, you can follow up on success by experimenting.
When to plant cover crops? I usually sow my cover crop seed in late summer/early fall so it can establish a little bit before winter. Then it will take off in spring.
Harvesting The Cover Crop
Cover crops for vegetable gardens are removed a few weeks before it’s time to seed, and usually at least a week before you transplant.
Giving the soil a few weeks to rest before you plant allows the cover crops to begin releasing nitrogen into the soil, and gives the allelopathic chemicals released by grass roots time to break down.
You’ll want to hoe down (I don’t mean the folk dance) most of your cover crop.
It’s best to incorporate it lightly into the top few inches of soil and leave some of it as a mulch, or second best would be to move it to the compost bin.
Farmers mostly use herbicides to kill the crop, but we’re trying to support the life in our gardens rather than kill it, so it’s worth relying on somewhat more labor-intensive tools like the hoe.
Any questions about cover crops for gardens? Or what do you use? Let me know below!