Interactive lesson

Green manures, step by step

Interactive lesson: cover bare soil — choosing the plant, sowing, nodules, ending in flower without digging and how much nitrogen is left.

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The whole lesson as text

1. Bare soil is lost soil

A bed left empty from August to April works against you.

No bare beds — The rule: no bed stays bare for longer than 4–6 weeks, and above all not over winter.
Catches nitrogen, loosens — Rye, phacelia, mustard and fodder radish catch nitrogen in autumn with fast roots before it washes out. Fodder radish loosens compacted soil with its deep root.
Legumes add nitrogen — Vetch, peas, field beans and clovers fix nitrogen from the air with the help of bacteria in their root nodules.
A mix is the safest — Rye holds the vetch upright and catches nitrogen; the vetch adds it. Together they cover the soil and smother weeds.

Why: Rain carries nitrogen down out of reach and fine soil down the slope. Sun and frost break up the soil crumbs, and weeds sow seed for the next three years. A plant sown after harvest turns all of this around.

Don't know what to sow? Sow a mix of a legume and a non-legume: it almost always does better than either plant alone.
In spring you cut the green manure and get mulch and worm food right where you need it.

2. Choosing the plant

Each job and each window in the year has a different best plant.

Fast cover — Phacelia reaches flowering in 6–8 weeks, buckwheat in 5–7. Both smother weeds and feed bees.
Not into cold soil — Buckwheat and phacelia are not sown until the soil is above 10 °C (50 °F). Buckwheat is killed by the first light frost.
Legumes and winter — For nitrogen sow legumes: vetch, peas, field beans, clovers. For winter, rye with winter vetch.
Mustard is a brassica — Mustard and fodder radish don't go before cabbage, kale, cauliflower or radishes: clubroot and flea beetles.

Why: Phacelia and buckwheat cover the soil fast and feed bees. Legumes bring nitrogen. For winter, rye with winter vetch is best, because it overwinters and gives the most mulch.

Phacelia germinates in the dark: the seed must be covered with 1–2 cm of soil.
Order winter vetch and crimson clover by July, because in September they are often sold out.