Green manures

To make your floor more alive!

Green manures remain unknown to many gardeners. However, this ancient practice is the basis of organic cultivation and enormous benefits result from its use.

Plants grown as green manure serve as temporary ground covers before being buried in the soil to enrich it with essential minerals for vegetable crops.

The advantages of green fertilizers

• They weaken and smother weeds.
• They prevent erosion, leaching and drying out of the soil by protecting it from the sun and wind.
• They improve the quality and structure of the soil.
• They enrich the soil with organic matter.
• They produce reserves of potassium, phosphorus or nitrogen.
• Their flowering attracts many insects and pollinators.
• They break the cycle of disease.
• They make excellent mulch when left on the surface after mowing.
• They help water seep into the earth when they are buried.

Backdoor cultivation

We call “backdoor green manures” those that we cultivate before or after the main crop.

Before a perennial or nutrient-demanding crop

The green manure technique is associated with crop rotation. Divide your garden into different sections and reserve one each year for growing green manure (two to three repetitive sowings throughout the season). The following year, plant the most demanding vegetables such as cucurbits (squash, pumpkins, cucumbers) and nightshades (tomatoes, eggplants, potatoes).

Before establishing plots of perennial vegetables or small fruits (asparagus, Jerusalem artichoke, raspberry, strawberries, etc.), sow successive green manures over two full seasons; the soil will be well enriched and perennial weeds (quackgrass and others) will be much less numerous.

After a main crop

In summer or at the end of the season, sowing green manure will enrich the soil, but it will also prevent erosion by covering your vegetable garden during the off-season. As soon as a crop is harvested and no other is planned to replace it, sow green manure, even in small spaces.

*After the garlic harvest at the end of July, or that of cool weather vegetables such as radishes, spinach and kohlrabi.

Intercropping

Green manure in intercropping is grown close to the main crop, for example, in alternate rows or in alleys to the sides of the main crop beds. It can be sown at the same time as the main crop or at a different time. Green manure sown at the same time has the advantage of not requiring any additional soil preparation. Legumes (peas, fava beans, clover) are easier to plant in intercropping than in cover crops.

At the ecoumene, we sow rows of rye or oats between the rows of cucurbits during their growing season. In a small garden, intercropping of fodder peas can be done with, among others, lettuce or garlic crops. In this case we can make rows of green manure alternating with the rows of the main crop.

Note: this method requires more attention, because the intercrop must be able to produce a good root and vegetative system without harming the main crop.

Variétés

Cultivated before or after your vegetable species, the grasses, brassicas and legumes used as green manure contribute to the health of the soil each in their own way.

• Grasses root deep and take up the nutrients found there, particularly nitrates, which are more mobile and easily leachable.
• Mustard and buckwheat are champions for extracting phosphorus, while cruciferous vegetables in general win the prize when it comes to potassium.
• As for legumes, they have no equal in fixing nitrogen drawn from the soil or captured in the air.
• In addition, all provide the soil with a good quantity of organic matter.

To know

• Before sowing, the stems and leaves of the plants grown in that location are cut.
• We work the soil and rake to eliminate clods.
• Sow densely with a seeder or broadcast.
• We rake again to mix the seeds with the soil on the surface.
• Water the seedling well to ensure rapid germination.
• Weeding is not necessary, but the flower spike of weeds should be trimmed with pruning shears before setting seeds.
• For a nitrogen supply which increases soil fertility, we mow the green manure before or at the start of flowering.
• For a carbon supply that increases the organic matter in the soil, we mow the plants at maturity (after flowering), in autumn or the following spring.
• Mowing is done with a mower or brush cutter. Annual species like buckwheat and oats have the advantage of not surviving the winter and can simply be buried in the spring.
• The mowing residue is left to dry on site before incorporating it into the first few centimeters of soil.
• After burying, dig lightly while incorporating ripe compost.
• We avoid deep burial.
• We wait two weeks before sowing another variety.
• We do not sow green manure from the same family as the crop planned for this location.

Oat —Avena sativa

Poaceae family

Seeding rate: 2 kg/100 m2

• Oats are a fast-growing grain that grows in all soil types. Germination takes place between 5 and 14 days.
• It can be sown as soon as the soil can be worked in April and until the beginning of September in soil between 1 and 24°C.
• It is broadcast and the plants are returned to the soil as green manure after 30 to 65 days.
• It is well adapted to cold conditions, but does not survive the winter.

Field bean – Vicia faba

Fabaceae families

Seeding rate: 2 kg/100 m2

• The field bean excels at fixing nitrogen in the soil.
• It resists cold well and tolerates poor or clayey soils and high levels of mineral salts.
• It can be sown as soon as the soil can be worked in April and until the beginning of September, in soil between 1 and 24°C.
• The seeds germinate in just 3 to 6 days.
• Sowing is done 10cm between the plants and they are returned to the soil as green manure after 30 to 65 days.

Mixed oats and peas – Avena sativa and Pisum sativum

Poaceae and Fabaceae families

Seeding rate: 2 kg/100 m2

• Oats and field peas form a very interesting duo:
• Peas grow at the same speed as oats, and are also very resistant to cold, still growing very late in the season.
• It provides the soil with a rich contribution of nitrogen.
• This mixture covers the ground very well, making it virtually impossible for weeds to establish.
• As with oats, this mixture is used over a period of ideally 2 months, before or after a main crop.

White mustard — Sinapis alba

Brassicaceae family                                          

Seeding rate: 500 g/100 m²

Mustard's rapid growth is just one of the qualities that make it an excellent green manure.

• Its deep roots excel at breaking up heavy soils and its aerial parts buried in the soil provide it with a first-rate nitrogen supply. 
• Its role as a nematicide is very interesting in plots where potatoes have been grown.
• Because it grows very quickly and does not fear root competition, it covers the soil without delay and protects it from erosion.
• Because it can grow 50-80 cm tall in a single month, mustard sowing can be done in spring, summer or fall.

Broadcast sowing, followed by raking to lightly bury the seeds

Fodder peas — Pisum sativum

Fabaceae families                                          

Seeding rate: 2 kg/100 m²

Forage peas benefit from inter-sowing, because their climbing stems benefit from a support to cling on.

• Compared to oats, the root mass of peas is very low, but its capacity to fix nitrogen in the soil is almost double.
• Unlike other green manures such as mustard, the aerial parts of the pea grow almost as much in soil previously enriched with compost or not.
• Its rapid growth and great resistance to cold allow it to be sown early in spring or autumn with excellent results.
• The dried aerial parts decompose very quickly in spring.

Buckwheat — Fagopyrum esculentum

Family Polygonaceae

Seeding rate: 2 kg/100 m2

• The growing time of buckwheat as a green manure is 30-65 days. Its well-branched root system allows good structuring of the first centimeters of soil.
• This plant is a phosphorus extractor which purifies the soil. It turns out to be the most effective for smothering weeds.
• Its flowers attract many beneficial insects.
• Very sensitive to cold, buckwheat must be sown once the risk of frost has passed (from the beginning of June to the end of July in soil at 15-25°C).
• The seeds germinate in 2 to 6 days and the plants are returned to the soil as green manure after 30 to 65 days.

Autumn rye — Secale cereal

Poaceae family

Seeding rate: 2 kg/100 m2

• Rye has a large fibrous root system that captures nitrogen from the soil very efficiently.
• This biennial variety survives harsh winters and uses soil moisture early in spring for rapid growth.
• The seeds are sown by broadcast on any free plot from the beginning of September to the end of October and germinate in 3 to 6 days (soil temperature between 1 and 20°C).
• The young plants are buried the following spring, two to three weeks before the vegetable crops are established.
• Their burial is more laborious when they are mowed at their full maturity.

white clover – Trifolium repens

Fabaceae family

Seeding rate: 1 kg/100 m2

• This slow-growing clover spreads by stolons and is a champion in the fight against soil erosion.
• Nodules present on its roots transform atmospheric nitrogen into mineral nitrogen.
• It tolerates poor soils and drought, but prefers cool, moist soils.

Updated 27.07.2023/XNUMX/XNUMX: spelling corrections and modification to the section on intercropping.