Garden Menu
Green Manures
Green manures are quick growing cover crops grown from seed with the long term aim of digging them into the soil to benefit the soils fertility and structure. Some plants such as Forage pea, Tares and clover have the advantage of fixing nitrogen from the air to the soil while growing, whereas Mustard has a sterilising effect when dug into the soil and its fibrous nature improves soil texture.
Green manures are a useful means of keeping cover over bare, fallow ground to prevent the growth of weeds and prevent leaching of nutrients from the soil. If helpful, they can be grown during the winter between vegetable crops to maintain ground cover.
Green manures are dug in a few weeks prior to the land being used for another crop. Therefore it is important to sow the seed well in advance to ensure the green manure crop develops fully. Plants should be dug into the soil before the stems become woody or tough and in many cases before they start to flower.
From the home sufficient point of view, green manures are a valuable and cheap means of improving soil quality while suppressing weeds and saving time on fallow ground. Many can also be utilised as fodder or grazing for livestock.
Both annual and perennial plants are used as green manures, some of these include:
- Alfalfa (Medicago sativa) aka. Lucerne
- Borage (Borago officinalis)
- Buckwheat (Fagopyrum esculentum)
- Comfrey (Symphytum officinale) Comfrey is an excellent green manure. If preferred, the leaves can be harvested and steeped and composted in a container of water to produce a liquid fertiliser rich in nitrogen and potassium!
- Crimson Clover (Trifolium incarnatum)
- Fenugreek (Trigonella foenum graecum)
- Blue Lupin (Lupinus angustifolius)
- Mustard (Sinapis alba) Part of the Brassica family. Do not use in rotation prior to growing brassica crops such as cabbages as there is a great risk of disease such as club root.
- Phacelia (Phacelia tanacetifolia)
- Red Clover (Trifolium pratense)
- Winter field beans (Vicia faba)
- Winter Tares (vicia sativa)
| Name | Plant family | Persistence | Height (cm) | Sowing period | Benefits |
|---|---|---|---|---|---|
| Alfalfa | Pea (Fabaceae) | Perennial | 75 | April - July | Nitrogen fixing |
| Borage | Borage (Boraginaceae) | Annual | 30 | March - May | bulky material |
| Buckwheat | Knotweed (Polygonaceae) | Annual | 30 | March - May | Cover crop, food for wildlife |
| Comfrey | Borage (Boraginaceae) | Perennial | 100 | April - July | Deep roots help break up heavy soils, liquid fertiliser, bulky compost material |
| Crimson Clover | Pea (Fabaceae) | April - September | Nitrogen fixing, | ||
| Fenugreek | Pea (Fabaceae) | Perennial | 60 | April - August | Nitrogen fixing |
| Bitter Lupin | Legume (Leguminaceae) | Annual | 150 | March - July | The best nitrogen fixer |
| Phacelia | Borage (Boraginaceae) | Biennial | 80 | March - September | Good for bees and insects, quick ground cover |
| Red Clover | Pea (Fabaceae) | Perennial | 40 | April - August | Nitrogen fixing |
| White Mustard | Cabbage (Brassicaceae) | Annual | 150 | March - September | Bulky material, Bio sterilant mustard has a natural soil steriising effect. |
| Winter Tares | Pea (Fabaceae) | Annual | 75 | March - September | Nitrogen fixing |