Green manure is one of the best and cheapest investments for organic garden soil. 🌿 An empty bed never stays empty — instead, green manure is sown to improve soil structure, fix nitrogen and feed earthworms. Based on the ÖMKi (FiBL) 2024 guide, here is how.
🌿 The most important green manure plants
| Plant | Sowing time | Main effect | Note |
|---|---|---|---|
| 🌼 Phacelia | Mar–Aug | Excellent soil loosener, bee forage | Best all-purpose green manure |
| 🌱 White mustard | Mar–Aug | Biological soil disinfection, weed suppression | Don’t sow after brassicas! |
| 🌿 Crimson clover | Jul–Sep | Nitrogen fixation 100-200 kg N/ha/year | Legume — essential in rotation |
| 🌾 Rye + vetch mix | Sep–Oct | Winter protection, nitrogen fixation | Best autumn cover mix |
| 🌱 Oil radish | Jul–Aug | Biological deep-loosener, nematode suppression | Thick taproot breaks up clay |
📅 When to sow green manure?
Late summer (August): After harvest, immediately sow phacelia + white mustard. They fix nitrogen, prevent winter leaching, and provide bee forage until September. Autumn (Sept–Oct): Vetch-rye mix for winter protection. Work in shallowly in spring. Spring (Mar–Apr): Phacelia germinates from +5°C — one of the earliest sowing opportunities.
✂️ How to incorporate?
- 🌸 Timing: at the start of flowering — nitrogen content is highest
- 🔪 Chop or mow before incorporating
- ⛏️ Shallow incorporation (10–15 cm) — deep incorporation causes anaerobic rotting
- ⏳ Wait 2–4 weeks after incorporation before planting
- 🌾 Alternative: cut and leave as mulch on the surface
✨ Summary
Green manure is one of the cheapest and most effective soil improvement methods — one packet of phacelia seed goes a long way. The empty bed works for you. 🌿
🔗 Related articles
- Earthworms and Soil Life – your garden’s best ally
- Improving Garden Soil – bio-intensive soil regeneration
❓ Frequently asked questions about green manure
Why must green manure be incorporated shallowly (10-15 cm) rather than deeply?
Deeper soil layers have less oxygen, so a large amount of fresh green biomass buried there decomposes anaerobically, producing foul gases and compounds that are toxic to plant roots. Shallow incorporation keeps the material in the oxygen-rich topsoil, where aerobic microbes break it down quickly and safely.
Why do you need to wait 2-4 weeks after incorporating green manure before planting?
As microbes break down the fresh biomass, they temporarily tie up soil nitrogen for their own growth, and intermediate breakdown compounds can inhibit germination or harm young roots. The waiting period lets these processes finish and releases the nutrients for the next crop.
Why shouldn’t white mustard be sown as green manure after brassica crops?
Mustard and brassica vegetables belong to the same plant family, so they attract and sustain the same soil-borne pests and diseases, such as clubroot. Sowing them back-to-back keeps that pest and pathogen population going instead of breaking its cycle.
Why is flowering the ideal moment to incorporate green manure?
A plant’s nitrogen and biomass content peaks around flowering, just before it redirects energy into seed production. Incorporating later, once seed has set, means dealing with woodier, harder-to-break-down stems and lower nitrogen content, since the plant has already moved its nutrients into the seeds.