Green Manure
A green manure crop is one that is grown over a season when the bed is not in use, often autumn and winter, and later tilled into the soil to improve the fertility. A green manure crop grown over autumn and winter also prevents the soil from eroding and compaction when not in use.
They are sometimes referred to as "cover crops". A cover crop should be tilled under about a month before
you plant.
This can present a problem in areas where the soil wet in
early spring. In these regions, plant your cover crop early so that
it can be tilled under in late autumn to decompose over winter. The damage
done by working wet soil outweighs the benefits of the green manure. Before
planting, clean up the garden area and remove all crop debris. Rake
the soil to remove clumps, and sow the seeds when rain is expected.
PROPERTIES AND USES OF GREEN MANURE
- Fast growing
- Smothers the soil to prevent weed growth.
- Replaces and holds nutrients.
- Improves soil structure.
- Utilises and "fixes" atmospheric nitrogen (Leguminous plants).
- After digging in they increase the organic matter content of the soil.
If at any time of year the soil is bare for six weeks or more, especially in the winter, nutrients will be lost through leaching from rain, snow and wind erosion. Green Manure helps to break the force of winter rain and maintains a more even soil temperature and moisture content.
Many green manures have root systems that grow deep to tap resources unavailable to some crops. Others produce a fibrous root system to help build structure in the soil, and many have flowers that attract pollinating insects.
GROWING GREEN MANURES.
Chose the type you require. This will depend on how long you wish to fill the space and when you are going to do it. Green manures are listed here with cultural information to help you choose.
Sow the seeds. Allow the plants to grow. Keep them watered and weeded if necessary.
When the soil is needed or when the plants are about to flower, cut them down and dig them in. The nutrients contained in the plants will be released for the benefit of the following crop.
WHEN TO GROW.
Apart from the depths of winter (Dec to Feb), there is a green manure crop that can be sown. You need to choose a type that will grow quickly at the time of year you wish to sow and also one that fits in with the amount of time you have free on your soil.
WINTER MANURES
Land is traditionally dug over and manured in autumn, then left bare over winter. Many nutrients can be lost during this time due to the leaching action of rain and snow.
Green manure that will survive the winter can be sown in the autumn while the soil still has some warmth left in it. In the spring this crop can be dug in. The nutrients held in the plants during the growing period are released after a period of two to three weeks and become available to a newly sown or planted crop.
GREEN MANURE FOR LATE SUMMER OR AUTUMN SOWING.
These will withstand moderate to hard frost for a long period and can be cut down in the spring.
- Alfalfa (Medicago sativa)
- Alsike Clover (Trifolium hybridum)
- Essex (Merviot) Red Clover (Trifolium pratense)
- Grazing Rye (Secale cereale)
- Phacelia (Phacelia tanacetifolia)
- Trefoil (Medicago lupulina)
- Winter field beans (Vicia Faba)
- Winter Tares (Vicia sativa)
GREEN MANURE FOR SPRING AND SUMMER SOWING.
These need to be quick growing to fill spaces for a short period. They are not generally frost hardy.
- Bitter Lupin (Lupinus angustifolius)
- Buckwheat (Fagopyrum esculentum)
- Fenugreek (Trigonella foenum graecum)
- Crimson clover (Trifolium incarnatum)
- Mustard (Sinapsis alba)
ALFALFA |
|
| Botanical Name | Medicago sativa |
| Sowing time | March to July |
| How to sow | Broadcast at 2 to 3 grams per square metre (1/8oz/sq yd) |
| Size (height) | 100 to 150 cm |
| Winter hardy | Yes |
| Nitrogen Fixer | Unlikely |
| Term of growth | Perennial. Grow for several months or more than one season. |
| When to Dig in | Anytime. |
| Difficulty digging in | Medium effort if young. Hard if left for more than one season. |
| Notes | Very deep rooting. Will grow on most soils. Dislikes acid or waterlogged soils, but drought resistant. Keep grazing animals away |
BEANS, Winter Field |
|
| Botanical Name | Vicia faba |
| Sowing time | Early September to Late November |
| How to sow | 10cm Deep in drills 15 to 20 cm apart (6in apart) |
| Size (height) | 60 to 90 cm |
| Winter hardy | Yes |
| Nitrogen Fixer | Yes |
| Term of growth | Overwinter |
| When to Dig in | Before flowering |
| Difficulty digging in | Medium effort |
| Notes | Will grow on loam or heavy clay. Not drought resistant. Slow to germinate. Sow close together to prevent weeds growing between plants. Cheap if you save your own seed |
BUCKWHEAT |
|
| Botanical Name | Fagopyrum esculentum |
| Sowing time | Mid March to Late August |
| How to sow | Broadcast at 10gm per square metre or thinly in shallow rows 20cm apart (1oz/sq yd) |
| Size (height) | 80 cm |
| Winter hardy | No |
| Nitrogen Fixer | No |
| Term of growth | 2 to 3 months |
| When to Dig in | Before or during flowering |
| Difficulty digging in | Easy, no effort. |
| Notes | Grows on poor soils. If allowed to flower, attracts Hoverflies to aid pollination of crops. Attracts bees and hoverflies |
CLOVER, Asilke |
|
| Botanical Name | Trifolium Hybridum |
| Sowing time | Early April to late August |
| How to sow | Broadcast at 2 to 3gm per square metre (1/8oz/sq yd) |
| Size (height) | 30 cm |
| Winter hardy | Yes |
| Nitrogen Fixer | Yes |
| Term of growth | Several months |
| When to Dig in | Anytime |
| Difficulty digging in | Medium effort. |
| Notes | Will withstand wetter soils than other clovers but more prone to drought. Shallow rooted. Better on low pH than other clovers |
CLOVER, Crimson |
|
| Botanical Name | Trifolium incarnatum |
| Sowing time | Early March to late August |
| How to sow | Broadcast at 2 to 3gm per square metre (1/8oz/sq yd) |
| Size (height) | 30 to 60 cm |
| Winter hardy | Mild winters only |
| Nitrogen Fixer | Yes |
| Term of growth | 2 to 3 months or overwinter |
| When to Dig in | Before flowering |
| Difficulty digging in | Medium effort. |
| Notes | Prefers sandy loam soil but will tolerate heavy clay. Large red flowers attract bees. |
CLOVER, Essex or Red Merviot |
|
| Botanical Name | Trifolium pratense |
| Sowing time | Early April to late August |
| How to sow | Broadcast at 2 to 3gm per square metre |
| Size (height) | 40 cm |
| Winter hardy | Yes |
| Nitrogen Fixer | Yes |
| Term of growth | Several months |
| When to Dig in | Anytime |
| Difficulty digging in | Easy, little effort |
| Notes | Prefers good loamy soil. Can be mown or cut several times per season and used for compost. |
FENUGREEK |
|
| Botanical Name | Trigonella foenum graecum |
| Sowing time | Early March to late August |
| How to sow | Broadcast at 5gm per square metre or thinly in 15cm shallow rows. (1/8oz/sq yd) |
| Size (height) | 30 to 60 cm |
| Winter hardy | Mild winters |
| Nitrogen Fixer | No |
| Term of growth | 2 to 3 months |
| When to Dig in | Anytime before flowering |
| Difficulty digging in | Easy, little effort. |
| Notes | Prefers good drainage but will tolerate heavy or light soil. Cut tops, leave roots |
LUPIN, Bitter |
|
| Botanical Name | Lupinus angustifolius |
| Sowing time | Early March to late June |
| How to sow | In rows 15cm apart, 2 to 3 cm apart in the rows. 3 to 4 cm deep. |
| Size (height) | 50 cm |
| Winter hardy | Mild winters |
| Nitrogen Fixer | Yes |
| Term of growth | 2 to 3 months |
| When to Dig in | Before flowering |
| Difficulty digging in | Easy, little effort. |
| Notes | Prefers light slightly acidic soil. Foliage not very dense. Deep rooted. Goes with dug-in sods. Good for compost |
MUSTARD |
|
| Botanical Name | Sinapis alba |
| Sowing time | Early March to mid September |
| How to sow | Broadcast at 3 to 5gm per square metre or thinly in rows 15 cm apart (1/8oz/sq yd) |
| Size (height) | 60 to 90 cm |
| Winter hardy | Mild winters |
| Nitrogen Fixer | No |
| Term of growth | 2 to 3 weeks or up to 2 months |
| When to Dig in | Before flowering, toughens up after flowering |
| Difficulty digging in | Easy before flowering |
| Notes | Prefers moisture retentive, fertile soil. A member of the Brassica family, so crop rotation cycle must be considered. Densely sown can clear wireworm |
PHACELIA |
|
| Botanical Name | Phacelia tanacetifolium |
| Sowing time | Mid March to Mid September |
| How to sow | Broadcast at 2 to 3gm per square metre or thinly in rows 20cm apart (1/8oz/sq yd) |
| Size (height) | 60 to 90 cm |
| Winter hardy | Yes |
| Nitrogen Fixer | No |
| Term of growth | 2 months in summer. 5 to 6 months overwinter. |
| When to Dig in | Before flowering |
| Difficulty digging in | Easy, little effort |
| Notes | Grows in most soils. Quick to grow in summer. If left, will produce mauve flowers which bees love. Seed may be hard to find: once begun. grow your own |
RYE, Grazing |
|
| Botanical Name | Secale cereale |
| Sowing time | Mid August to late November |
| How to sow | Broadcast at 30gm per metre or thinly in rows 20cm apart (1 oz/sq yd) |
| Size (height) | 30 to 60cm |
| Winter hardy | Yes |
| Nitrogen Fixer | No |
| Term of growth | Autumn to spring |
| When to Dig in | Before flowering |
| Difficulty digging in | Hard work |
| Notes | Grows in most soils. Keep watered during germination, else yield is poor. Sow thickly to smother weeds. Heavy cover, good on most soils |
TARES, Winter |
|
| Botanical Name | Vicia sativa |
| Sowing time | Early March to Mid September. Avoiding June. |
| How to sow | Broadcast at 20gm per square metre or in rows 15cm apart and 4 to 5 cm deep |
| Size (height) | 50 to 75 cm |
| Winter hardy | Yes |
| Nitrogen Fixer | Yes |
| Term of growth | 2 to 3 months or Overwinter |
| When to Dig in | Up to flowering |
| Difficulty digging in | Easy, little effort |
| Notes | Prefers heavy soils. Dislikes light or acid soil. Produces dense cover. |
TREFOIL |
|
| Botanical Name | Medicago lupulina |
| Sowing time | Mid March to mid August |
| How to sow | Broadcast at 1.5 to 3gm per square metre |
| Size (height) | 30 to 60 cm |
| Winter hardy | Yes |
| Nitrogen Fixer | Yes |
| Term of growth | Several months to a year |
| When to Dig in | Anytime |
| Difficulty digging in | Medium effort. |
| Notes | Will grow in most soils but dislikes acid. Can be used for undersowing. Dense foliage |
