Green manure, use cover plants to fertilize the next harvest!
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A carpet of mustard, phacelia or clover thrown across an empty plot within days of harvest: green manure is simply fast-growing cover whose roots bind the soil and thread through it, leaving it lighter. Cut and bury it before it sets seed and it rots down into nutrients for the next crop.
Green manure is what fast-growing plants used to cover the ground are called after a plot has been harvested. Medick, clover, mustard, phacelia, white lupine, rape… these are all useful plants.
If sown in the vegetable patch as soon as the ground is bare, they keep weeds from settling in, avoid erosion due to rain, and for places with high slopes, they guard against landslides. Their roots hold the soil together and thread through the ground, making it lighter. Once they’re buried, they break down and provide nutrients that make it richer.
Which green manure for which plot?
The plants sold as green manure are not interchangeable: soil type and the crop that follows both narrow the choice. Here is what the article says about each of them.
Whatever you plan to grow later on the plot can influence the decision, too.
Planting green manure
Green manure is sown just like a lawn, simply broadcast on soil that has simply been run over with a rake. You can sow at the beginning of spring, the end of summer or in fall, before it freezes. A good practice is to sow just after you’ve harvested.
Broadcast seed, cover thinly, firm down and water
Cover with a thin layer of soil, press down, and water.
Germination will only take a couple days.
The plants can stay in place from 2 to 6 months depending on the species.
After that, before the plants bolt or go to seed, mow the green manure on the patch or cut it with a scythe, dry it for a few days and turn the soil over to bury it with a spade. Four to eight weeks later, depending on the plant, you can start your seedlings and regular crops.
It is also possible to use cut green manure for mulch, to protect spring seedlings.
How to choose your green manure?
Medick is one of the best covers for clay
Depending on your soil type, some plants will do a better job than others. Medick and mustard are great green manure for clay soil, while phacelia will grow on any type of soil. Whatever you plan to grow later on the plot can influence the decision, too.
Clover locks nitrogen from the air into the soil
Best avoid growing Brassicacaea or cruciferae (radish, cabbage, watercress, turnip…) after mustard, rape or turnip rape, because the same diseases can transfer to all of these species.
Conversely, clover is recommended after brassicaceae plants because it locks nitrogen from the air into the ground, and the brassicacaea or cruciferae tend to deplete it.
Laure Hamann
Written by Gaspard Lorthiois | Loves helping out, especially when it comes to growing things. Worked in herbal medicine, runs a farm, and dabbles in tech. Master's degree and engineer.
