Protect and enrich the soil with a vegetal cover.

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Vegetation cover is in agriculture an intermediate culture between two production crops. Do not confuse with a “cover” of the soil, that is to say the fact of covering its soil with mulches, green manures, mounds of culture, and especially the thatched roofs.

Sexy subject, is not it? Why did you decide to talk about plant cover in an article, when it’s an agricultural practice and our subject is the garden? Because plant cover crops are an alternative to plowing – which deteriorates the life of the soil – and to mulching – which requires inputs of materials very quickly unsustainable if we have a little surface. Anyone who has already mulched a garden of 200m ² can tell you about it. 
Clearly, plant cover is the future of agriculture and the natural garden .

The challenges of using a plant cover

Improve fertility

We had already spoken in our article about the difference between the “earth” and a living soil of the root property to promote life to them. Comparatively, mulched soil is more alive than bare soil, but densely planted soil is even more so. 
Roots allow living organisms to survive more deeply, and allow for better diversity. The result is increased fertility . As a result, as long as the crop lasts, the soil is fertile, it breaks down the organic matter and makes it available for the next crop.

Fix nitrogen

Fixing atmospheric nitrogen is a unique property of plants of the family Fabaceae , through symbiotic bacteria. This is important because for some soils nitrogen is an overall fertility limiter, so you have to start by stocking it before you fertilize it. 
Decomposers – bacteria and fungi – feed on ammonia (NH4 +), so a nitrogen-poor soil will also be unable to start its carbon cycle, or it will idle.
Traditionally, this problem was addressed by spreading manure on poor soils grown in crops, followed by nitrates in the chemical area. Seedlings of Fabaceae are an interesting alternative because their decomposition feeds the soil gradually, unlike conventional fertilizers. This is important if we want the soil life to adapt gradually.

Avoid weed invasion of crops

In the natural garden there are not really weeds, just plants that germinate where the conditions are right for them, and can show imbalances – see our article on bioindicators . However, the use of specific cutlery can avoid the installation of some unwanted spontaneous because too difficult to remove for the installation of the new crop.

Nourish local life

In addition to feeding the soil, grassland plants generally used as cover crops host a great many insects– including pollinators, and predators of parasites – and vertebrates. An intermediate crop in the kitchen garden serves as a refuge for a useful life – or not, it is free – for the gardener.

Protect the soil.

Plant roots protect the soil from erosion, leaching of nutrients, and compaction by rain . We regularly hear that we must never leave a bare ground, and all plant covers meet this need.

Define your need

The vegetation cover potentially has various properties to meet the issues mentioned above. Before defining which species come into the one you plan to sow, you need to define the need. Here are the three most common cases.

Preparation of a soil never grown

Looking at species that grow naturally can help you know if you need to decompact, enrich, or fertilize instead. This is explained there .

Fertilization of an already cultivated soil

If you grow a garden, you should know that most vegetables do not energize the soil. So after one or more crops this one needs plants that contribute to its fertility. It is therefore interesting to sow a “green manure” – which is also a “green fertilizer”, by the way. Green manures are typically sown between a spring crop and a late-season crop, or fall. They stay in place for a few months – often 3 to 6 – and then they are destroyed by mowing or grubbing to spread them on the ground where they serve as mulching.

Soil protection

    • For the winter : a rich and healthy soil can not remain if it is not protected during the winter, so there are blankets that do not serve as fertilizer, but first of all physical protection.
    • In -season : light soils must be “armed” by constantly roots, the risk that erode the seasons. Some very specific cutlery are involved, for example, in the fixation of dunes or shorelines.

Which species for what use?

White mustard : its first interest is its very fast emergence which takes speed of the other plants. It also prevents the leaching of nutrients. Sowing in spring or autumn. Phacelia : a good melliferous plant that uses its deep root system to raise nutrients and decompact the soil. Sowing in spring until summer. 

Alfalfa : this Fabacea is not only intended to feed pets, it fixes atmospheric nitrogen. Sowing in the spring. 

Vetch : another Fabaceae that fixes nitrogen from the air, and can also attract bees and auxiliaries. Sowing in spring or autumn. 
peaspeas also participate in nitrogen fixation. Sowing in spring or summer.

Oats : use with caution because it is sometimes difficult to get rid of, but oats dig deep into the soil to feed and protect it densely. Sowing in spring or autumn until December. 

Beans : or fababeans. Still a nitrogen fixator that is conventionally used in winter cultivation, to protect the soil and fertilize it. Sowing in spring or autumn. 

Buckwheat : easy to grow on difficult soil, buckwheat fixes nutrients and converts them into organic matter. Sowing in the spring. 

Lin : his interest is mainly to promote biodiversity, because it sometimes germinates more slowly than other species. Sowing in spring or autumn.

The list does not stop there, there are many beneficial annuals on the ground.

Important tips:

  • The more species you mix, the better the soil fertility , thanks to the diversity of decomposers and physicochemical processes.
  • We did not mention here the white clover , which is a good cover, but is a little difficult to remove because it is a perennial rooted well. It is however quite valid for a permanent cover.
  • You can of course add annual flowers – cosmos, blueberries, nigelles – in your mix for fun!

Install the plant cover.

We proceed by sowing, as for a turf. The idea is to prepare its surface finely – to the rake – after having decompacted a few centimeters. No need to “pass the tiller” before this kind of sowing, which makes him lose part of his interest, which was to avoid plowing. 
Then it is advisable to sow regularly, on the fly. Mixing your seeds with sand in a bucket allows you to have a visual cue to control the regularity of the sowing. Finally, it is necessary to “roll” its sowing, which consists of tamping the soil to the surface to bring the seeds into contact with the soil. 
Depending on the season, it may be necessary to water the first few weeks.

Dr. Kimberly Seltzer

Postdoctoral Scholar, UC Berkeley Research Assistant, MIT

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