In permaculture, one of our main preoccupations is that of building soil and fertility. It’s a means by which the practice of permaculture food production is something far more significant than mere sustainability or organic gardening. The idea is to have a positive, not just neutral, effect on our landscapes and the planet. Breaking even isn’t enough; we have to revitalise.
Under this creed, taking care of our gardens and the soil life within them has moved us away from conventional, “Green Revolution” style farming techniques of heavy irrigation, chemical fertilisers, and reduced biodiversity. This methodology, of course, also ultimately incorporated (and relies upon) a slurry of biocides. Instead, permaculture has adopted systems that are more cooperative, and less combative, with nature.
There are many means by which we keep soils fertile and, in fact, improve upon them. We avoid tilling. We mulch heavily and plant diversely. We look to perennial food sources rather than the more demanding annuals most of the world’s food production focuses on. Nitrogen-fixers are used and we compost. Plus, amongst numerous other low-maintenance and cyclical efforts, we plant cover crops.
Why Plant Cover Crops?
With anything we do in permaculture, we are looking for function stacking, ecosystem enhancement, and easy (but environmental-friendly) application. Cover crops are very much in line with all of this. They are yet another example of a designer’s ability to utilise natural cycles to enhance natural systems. Cover crops are doing several things:
- Adding fertility: Cover crops, particularly those with nitrogen-fixing abilities, enhance the fertility of the soil. Aside for nitrogen-fixing, though, the simple act of feeding our cover crops right back to the earth creates a continually loop of nutrients that can rival compost and manure.
- Improving soil texture: Plants can be specially selected because they have roots that break up compacted soil—think daikon radish—or roots that hold together loose soils—the fibrous roots of annual rye. Regardless, the organic matter added both below and atop the surface will improve soil texture.
- Preventing erosion: Cover crops protect the soil from drying out in the sun and being carried off by wind. They hold the soil in place during the rain, while at the same time, buffering the rainfall so that it doesn’t compact the garden.
- Increasing moisture retention: Adding organic matter to the soil dramatically increases the moisture retention, the matter sponging up the water when it’s there and holding it in place so that’s available when rains are sparse.
- Stopping weed growth: An empty garden is an invitation for weeds, but cover crops, which are typically grown densely, fill the niche weeds would take and, by design, will outcompete the plants we might not want growing somewhere.
Furthermore, there is a lot to be said for the fact that they are simply keeping the soil active.
When to Plant Cover Crops
Basically, the best time to plant a cover crop is anytime there isn’t something growing in a garden or field. Rather than allowing the garden to sit stagnantly, the cover crop will keep the soil life occupied while providing all of the benefits listed above, ultimately supplying the mulch for the next planting cycle.
With that in mind, two common times to plant cover crops are in the summer lull between early spring crops and fall plantings, as well as over the winter. For the summer crop, the goal is to get something up and gone in a short span of time. It’s not a bad idea to sow shortly before or right after the spring food crops are gone. For winter cover crops, the crux of success is choosing plants that will do well in the frigidness of your particular climate then getting them in the ground soon enough for them to establish before temperatures drop too much.
What are Some Good Cover Crops?
The answer to this can be simple, and there are plenty of standby plants to choose from. That said, it wouldn’t be the permaculture way to choose a cover crop arbitrarily. Instead, we’d want to define “good” as providing some particular function we are after. In other words, what do we want to accomplish with the cover crop? Are we looking to break up compacted soil? That might require something different than wanting a quick turnaround or a low-growing canopy or a boost in nitrogen. Cover crop plants, when chosen thoughtfully, can accomplish more.
- Buckwheat: This is the go-to, quick-turnaround cover crop for the summer lull. It’ll grow into something worthy of mulch in less than two months. It is also good for cultivating in lacklustre soils, such as in the beginning stages of soil conditioning, and can overshadow weeds. It must be cut before it sets seed.
- Clover: A nitrogen-fixing legume, clover is good for adding fertility, and the blooms will also attract pollinators. Clover is also good at suppressing weeds and tolerating a variety of conditions. There is a good type of clover to grow in most places.
- Cowpea: Another nitrogen-fixing legume, cowpeas are a tender, summertime cover crop that’ll put some fertility back in the soil. They are quick growers, have deep-reaching taproots, and attract beneficial insects even without flowering. They won’t tolerate cold.
- Hairy Vetch: Hairy vetch is a hardy, nitrogen-fixing cover crop. It should be planted about a month before the first frost, and it will grow throughout the winter, presuming snow cover isn’t an issue. This popular cover crop will rebound big-time in the spring, creating a lot of biomass before being cut down for spring garden mulch.
- Mustard: A popular choice in Britain. Mustard is a popular choice because it has a compound, glucosinolates, which helps get rid of soil-borne pests and diseases. It’s considered a biofumigant. Mustard is cool season crop that will winterkill a little below freezing. If it is allowed to set seed, it will come back.
- Oats: Though they lack to the nutritional wallop of other cover crops, oats are considered a versatile cover crop and good for planting in mixes, working cooperatively with radishes and clovers. They are also a great choice for particularly, maybe overly, moist soils.
- Radishes: There are several types of radishes commonly used as cover crops. They are renowned for providing a good canopy, alleviating compaction, and scavenging nutrients. Radish roots are left in the soil to create biological pathways for other roots to establish.
- Rye: There are both annual and perennial winter (aka cereal) rye. Both are good for breaking up soil, over-wintering, and biomass. It is often planted in conjunction with a nitrogen-fixing legume, such as hairy vetch or clover.
Include Cover Cropping
An erroneous assumption is that cover cropping, aka green manure, is only for large-scale applications. In fact, garden beds, too, will benefit greatly from including cover crops in the cultivation rotations. Many growers will actually plant some nitrogen-fixing cover crops as intentional weeds beneath mature, month-old annual crop plants. In essence, this is the line in which a cover crop becomes a living mulch. Normally, though, cover crops are sown like small patches of lawn. It’s also important to cut the greenery down about three weeks to a month before planting.