Green Manure Crops
Ten Good Reasons to Grow a Green Manure Crop!
- They're cheap and easy to grow.
- A packet of green manure seeds is easy to carry home - unlike a large sack of animal manure!
- They can increase soil fertility.
- They improve soil structure and help prevent soil erosion.
- They encourage efficient use of land. So why not grow a green manure crop on your unused land this winter?
- Most green manure crops are very attractive to wildlife.
- Bare soil encourages weed growth, so green manure bare ground to keep weeds in check.
- By taking up nutrients from the soil, green manure crops prevent them from being washed
away when it rains.
- Some green manure plants (legumes) are nitrogen fixers.
- Green manuring increases the humus content of the soil.
How does Green Manuring Work?
Traditionally, green manure crops are sown and allowed to grow, either until the land is needed
again or until the plants have reached a certain growth stage. At this point, they are cut down,
dug in to the soil and are left to decompose, releasing vital plant nutrients back into the soil
which are then used by the next crop. Obviously, if you are using strict no-dig, veganic gardening methods,
then digging the crop into the soil is not really an option. But if you don't want to dig,
then green manure crops can also be composted or used as a mulching material instead. (More information on this later.)
Which Green Manure Plant Should I Use?
There are many varieties of plants which are suitable for use as a green manure crop and some of these are
listed in the table below. (Comfrey and sunflowers can also be used for this purpose too.)
However, if you do not have enough land left, to devote entirely to growing
a green manure crop, it is also possible to sow some green manure crops (e.g white clover) on
paths between beds. And crops, such as field beans, can even be sown in between rows of vegetables
in your raised bed system if you are short of space. Mixtures of green manure plants can also be
used. For example: fieldbeans/mustard; or vetch/clover/rye. If you would like more information on
sowing a mixture of green manure crops and some idea of the proportions of seeds to use, then
you should consult Vohan News. Issue 1. Pages 10-12. Copies of this publication can be obtained
from:
David Graham, Anandavan, 58 High Lane, Chorlton, Manchester M21 9DZ. (Phone: 0161 860 4869)
When selecting the crops that you are going to grow, you should bear in mind the following points:
- Choose either a quick or a slow-growing crop - to fit in with the time that the land will be
left vacant.
- The season of the year. (Not all varieties will survive the winter.)
- Whether you want your crop to fix nitrogen or not.
- Your soil type and how much drainage it offers.
Note: Plants marked * are all nitrogen fixers.
| NAME | LATIN NAME | WINTER HARDY | SOWING TIME | WILDLIFE VALUE | GROWING TIME |
|---|
| Alfalfa | Medicago sativa | Yes | Apr-July | Bee | 1-2 mths or a few yrs |
| *Winter Field Beans | Vicia faba | Yes | Sept-Nov | Bee plant | overwinter |
| Buckwheat | Fagopyrum esculentum | No | March-Aug | Hoverfly nectar | up to 2-3 mths |
| *Clover, Alsike | Trifolium hybridum | Yes | Apr-Aug | Bee plant | 1-2 mths or a few yrs |
| *Clover, crimson | Trifolium incarnatum | Possibly | March-Aug | Bee plant | 2-3 mths |
| *Clover, Essex red | Trifolium pratense | Yes | Apr-Aug | Bee plant | 1-2 mths or a few yrs |
| Fenugreek | Trigonella foenum graecum | Possibly | March-Aug | Butterfly nectar | 2-3 mths |
| *Lupin, bitter | Lupinus angustifolius | Possibly | March-June | Bee plant | 2-3 mths |
| Mustard | Sinapis alba | Possibly | March-Sept | None | 2-8 wks |
| Phacelia | Phacelia tanacetifolia | Yes | March-Sept | Bee plant | 2 mths(summer), 5-6 mths (winter) |
| Rye, grazing | Secale cereale | Yes | Aug-Nov | Bee/caterpillar food | autumn-spring |
| *Trefoil | Medicago lupulina | Yes | March-Aug | Bee/butterfly nectar | up to a few yrs |
| *Tares, winter | Vicia sativa | Yes | March-Sept | Bee/butterfly nectar | 2-3 mths or overwinter |
Note: Both, winter field beans (Vicia faba) and grazing rye (Secale cereale)
can still be planted this month, according to the table above. So, there may still be time to
green manure some land this winter! However, I would recommend that you try sowing a few seeds
first, in order to find out if they will germinate. I sowed field beans outside in
October and so far they have not germinated. However, my plot receives no sun at this
time of year and you may find that you are able to germinate field beans successfully in November,
if you have a sunny spot in your garden. It is of course perfectly possible to germinate the
seeds indoors and plant them outside later, if you are having any difficulty. I did this
and despite a battering by recent gales, I now have field beans growing in my tomato
patch. And, if all else fails, then field beans can also be sown early in the year - so delay
sowing your seeds until the spring!
When is the Crop Ready for Use?
On the whole it is better not to leave your green manure crop in the ground for too long, as land
occupied in this way can not be used for growing other crops. Also, if green manure plants get too
old, then they can become tough and will take longer to decompose and be incorporated into the soil by
soil organisms. For most green manure crops, it is usually recommended that they are cut and used before they
flower.
How to Use Green Manure Crops
Usually, green manure crops are cut down and dug into the top 15-20 cm of soil with a spade.
But, veganic gardeners, or anyone else who wishes to avoid digging the soil, can simply hoe off
young plants (or chop down older ones) and leave them on the soil surface as a mulch.
If plants are chopped down, then to prevent any regrowth of the stubble, cover the ground with a
light-excluding mulch (e.g. black polythene/newspaper) until you are sure that the green manure crop is
dead. If you are in a hurry to start replanting the ground, then you can of course simply plant through the mulch.
In any case, you will need to allow several weeks before planting the next crop in the mulched area,
in order to give the mulch some time to decompose and release its nutrients back into the soil.
Alternatively, if you do not wish to use your crop as a mulch, then you can compost it instead.
Composting is in fact a very good way of using up any crops which have been allowed to get too
old and tough!
Suppliers of Green Manure Seeds
You may be able to obtain a stock of green manure seeds locally, either from a garden centre,
or from a gardening shop. But, if this is not possible, then seeds can be obtained from
one of the following mail order suppliers:
- The Organic Gardening Catalogue (Address).
Stocks of the following varieties of green manure seeds are listed in their 1997 catalogue:
alfalfa, agricultural lupins, agricultural mustard, buckwheat, 4 varieties of clover,
fenugreek, field beans, Phacelia, tares, trefoil and Hungarian grazing rye. They also produce a
very useful leaflet called 'Gardening with Green Manures'. Price 0.75
- Suffolk Herbs (Address)
- John Chambers' Wild Flowers (Address)
This company offered a good selection of green manure crops in their 1996 Catalogue. Seeds sold by the kilogram.
(Minimum quantity 1/4 kilogram.)
Back to November 1997 Issue
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Copyright © Pauline Lloyd 1997.