Green manures for spring
 (Read 100+ times)
By Emma Cooper
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Spring is a busy time for gardeners, with seeds to be sown, digging and planting to be done, and the first weeds making an appearance. Green manures may not be the first things that you think of to sow, but there are many green manures that are ideal for spring sowing and bring many benefits to your garden.
At this time of year there are two primary benefits to sowing a green manure. If you have bare ground that you’re not going to cultivate in the next few weeks then sowing a green manure helps to avoid weed problems and add fertility to the soil. Choose the green manure you sow according to the amount of time your soil will be fallow – there are varieties that mature in a few weeks and some that can be left in place for much longer times. This is an ideal way to get a new allotment under control – cultivate a small portion for now, and sow green manures on the rest until you’re ready for more.
Green manures are crops grown specifically to add nutrients to the soil. They are dug into the ground before they flower and get tough and woody, and left to rot down and add organic matter. Some green manures are also nitrogen fixers, able to actively add nitrogen to the soil and make it more fertile. If you’ve got a patch of soil that will be vacant for 2-3 months, then sowing a nitrogen-fixing green manure will give your next crop a big boost. Some green manures can even be used to under sow permanent plantings – adding fertility as they grow, without disturbing your perennials.
You can also grow a patch of green manure to cut and use as a mulch elsewhere, or to provide green material for the compost heap.
When you’re choosing a green manure to sow in spring, you need to take several factors into account. The first is the sowing time, as some can be sown earlier in the year than others. The second is the length of time that you want the green manure to be in place for. The third is what benefits you are hoping to achieve – do you need a nitrogen fixer, or are you looking for a green manure that gives excellent weed suppression? And last, but by no means least, if you are using green manures on your vegetable plot then you need to keep your crop rotation in mind – some green manures are from common vegetable families, and need to be used in accordance with the rotation.
Nitrogen fixers you can sow in early spring include Crimson clover and lupin. Both can be sown right through into summer, are left in place for 2 or 3 months and prefer lighter soils. Fenugreek is also a nitrogen fixer, if you have suitable bacteria in your soil, and prefers well-drained soil. Fenugreek will inhibit seed germination – good for weedy plots, but you will have to wait several weeks after digging it in before you can sow seeds. Transplants will be unaffected.
Trefoil is another nitrogen fixer. Its claim to fame is that it can tolerate some shade and is very low growing – ideal for under sowing hungry plants, and you can leave it in place for months (it may even survive the winter).
Mustard is quick growing, needing only 1 to 2 months in the soil. It’s a member of the Brassica family though, so be careful with your crop rotation. Phacelia needs a month longer, but isn’t related to vegetables. And if you can let a small patch flower, the bees around your patch will love you for it.
As spring moves on you can sow Essex red clover, a nitrogen fixer that can be left in place for up to 18 months. You can even sow winter tares for a quicker nitrogen boost – they take 2 to 3 months to mature.
And by late spring you can be sowing alfalfa, a nitrogen fixer that should be left in place for a year or longer to have the most effect. Buckwheat is the best choice for poor soils, giving a nutrient boost in 1 to 3 months.
Whichever green manure you choose, remember to dig it in (or cut it down, if you follow the No Dig approach) before it flowers, when the growth is softer and will be incorporated into the soil more easily. Then sit back and let the earthworms and other soil creatures do the rest of soil improvement for you.
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Author Bio Box: Emma Cooper
Emma Cooper has a weekly gardening podcast, The Alternative Kitchen Garden, all about growing your own food in an environmentally friendly way. Check out her website for her gardening blog and more articles.
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