Some super benifical fall-planted cover crop plants: daikon, vetch, rye and wheat.

A fall cover crop of wheat, vetch and daikon radish fills the space between rows of summer millet that has finished.

The late summer/early fall  is the perfect time to think about fall planted cover crops.  Cover cropping is not just for big acreage, it’s great for gardens and even small container gardens.

The main objectives of planting a cover crop are to maintain soil fertility by holding or adding carbon and nitrogen in the soil and by controlling weeds. Cover cropping also attracts bees, other beneficial insects and can prevent erosion.

Permaculture principle: Use niches in space and time.

A less than fertile garden bed. After harvesting potatoes this is an open niche. If I don’t fill it the weeds will be happy to take advantage of the disturbed soil.

In an ecosystem a niche is an opening or availability of physical space for something to live in and grow.  The time element is important because the same physical space can have many different niches depending on the time of day and the season.  Sudden changes in an ecosystem lead to distinct openings. For example, a wildfire in a pine forest: fire opens all sorts of niches, even as it destroys existing ones. The aspen trees which have been struggling in the shade of the evergreens suddenly get light and they burst into growth, filling the niche.

By understanding the principle of niches we can pay attention to openings and make strategies to fill them with productive and useful elements. Planting cover crops is a great way to put the principle of niches into action.

Fall cover crop favorites:

Daikon radish

Raphanus sativus var. longipinnatus. A volunteer daikon radish, a member of the brassica family.

Here’s a young daikon radish already digging into the soil.

Daikon is a work horse of the garden. It has delicious edible roots, greens and seed pods. Bees and beneficial insects love its abundant flowers.

Its deep tap root can punch into heavy clay soil and if left unharvested will decay quickly, opening the way for oxygen and moisture that helps feed soil fertility.

Daikon germinates and grows quickly even in marginal soil, shading out nearby plants and weeds. However, it does need additional irrigation to thrive here in Western Colorado.

In the heat of late spring and summer, daikon bolts quickly to seed and the root gets pithy and tough. If edible roots are desired, early to mid September is the best time to plant. Harvest will be after the root is sweetened by frost.

The root will freeze and die over the winter, so re-seeding is necessary in the spring. Daikon is also a great spring cover crop, it will not produce great edible roots, but grows quickly, feeds the bees with abundant flowers and chokes out weeds. The immature seed pods are also a tasty addition to stir fries and salads.

Hairy Vetch

Vicia villosa, hairy vetch or winter vetch.

Vetch is known for its cold hardiness and ability to fix nitrogen. It forms a relationship with special bacteria in the soil that pull nitrogen from the air and ‘fix’ it in nodules on the roots. If the right bacteria is not already present in the soil it can be added as an inoculant coating on the seeds.

The nitrogen it ‘fixes’ will be mostly used by the vetch itself, however nearby plants can also benefit. The nitrogen available to other plants is increased substantially if the vetch is cut down before it goes to seed, releasing the stored nitrogen into the soil. If you dig up a vetch plant look for little pink nodules on the roots.

Vetch can take advantage of fall moisture to germinate and start growing, its frost tolerance allows it to continue to grow even as other plants freeze and die. In the spring it rebounds quickly and smothers out weeds as it adds nitrogen to the soil. It has a semi vine habit that climbs up other plants and structures.  It also has beautiful purple flowers that attract tons of bumble bees.

 Winter Rye and Winter Wheat

Triticum aestivum, winter wheat.

A thick winter rye cover crop with vetch starting to climb up.

Over wintering grains germinate in the fall, get established and then patiently wait until spring to burst vigorously into growth.  Many of the plants we don’t like, aka: weeds,  also germinate in the cold. They go dormant across the winter and emerge in the spring when there is available moisture in the soil. The niche that is filled by these weeds can be filled by productive and useful crops. Winter rye is a bit more hardy in the cold and can germinate almost up to freezing temperatures; it will start growing around 40 (F) degrees in the spring.  The thick matted roots (carbon) help create good soil structure and make great habitat (and food) for beneficial life in the soil. Winter grains ‘soak’ up free nitrogen that might other wise wash  away when nothing is growing, since nitrogen can be water soluble.  They then ‘carry’ the nitrogen into the next growing season. When dried, the stalks (straw) are high in carbon that make a great mulch and slow fertility builder.

Creating a ‘guild’ of cover crop plants

‘Guild’ is a permaculture term used to describe groups of plants (and/or animals) that work well together. A guild is similar to an ecological community. Instead of occurring naturally, a guild is designed with the intention of grouping plants together that will mutually benefit each other and also serve specific functions for us.

Green manure

A one shovel soil profile. The lower part is pure clay, but above it topsoil is starting to from after one season of cover cropping.

Chlorophyll gives leaves their green color, but all living ‘greens’ are also rich with nitrogen. When a green plant dies, as it turns brown, the nitrogen is released back into the air. However if we cut a green growing plant and dig it into the soil, bury it in mulch or add it to a compost pile, the nitrogen becomes available as food for life in the soil.  This is multiplied if we are cutting a nitrogen fixing plant like vetch. See my quick soil science post for more info on how this happens.

The process of ‘turning in’ a cover crop should be done 2 -4 weeks before planting the next crop in order to allow time for decomposition. The wait time will depend on how actively your soil is decomposing. This type of cover cropping is often called a “green manure”.

Growing our own mulch

If a cover crop is not turned in then it will grow to its full term and produce seeds which can be harvested for food or for planting future cover crops. The leftover organic matter can be collected, composted or simply let to rot over the winter. If we cover crop the entire garden area then there will always be plenty of mulch when needed, with the added benefits of soil conditioning and added carbon from the roots, and beneficial insects enjoying the flowers.

Putting it all together

This guild of plants – daikon, vetch and rye/wheat – work in harmony to protect bare soil from the sun and wind. They buffer heavy rain and reduce potential erosion.

Planted together, the daikon germinates first and grows quickly, creating shade and protection for the vetch and rye or wheat. These cover crops can be cast right into an existing garden and allowed to germinate under the other plants as they finish ripening and are harvested.  As fall progresses into winter, the daikon gets its tap root into the soil, but its broad leaves freeze and let more sunlight onto the vetch and rye. In the spring both the vetch and rye and/or race to use the sun and moisture. The vetch provides nitrogen for the rye or wheat, and the rye provides a trellis for the vetch to climb up. A thick and deep cover is formed.

While this is a simple three species cover crop guild for over the winter there are many more beneficial plants that can be added. The summer has a whole other set of plants. In situations where a perennial cover is desired there is yet another amazing group of plants.  So, pay attention to niches and fill them with as many useful and beneficial plants as you can find.

Some more examples of cover crops and niches