Is green manure a mystery to you? Wondering where to start? Sounding very confusing and complicated?
Fear not, we have a super simple guide to demystifying the world of green manure. By the end of the article, we guarantee that you will no longer be a green manure virgin!
In a super simple, non-technical, and jargon-free way, designed to help those that have never sown green manure before, the 5 steps will cover the following topics: Crop / Soil / Time of year / How to sow / Digging in.
By the end of the 5 topics, you will be clear on what to do and how to do it. So that you can have beautiful soil, naturally...just like Rekha!
Checkout Rekha on Instagram and see her beautiful soil!
For the last 5 years, Rekha has used green manure and you can see how it has improved her crops and her soil...the natural benefits of green manure are plain to see!
We shall start the series with the Crop...
The first question to ask is...do you need to fit into a crop rotation plan?- If you want to avoid a build-up of soil pests & diseases it’s important to follow a crop rotation plan [here]
- The usual rule is Roots (Carrots) > Legumes (Peas, Beans) > Brassica (Cabbage)
- For example, Winter Tares is part of the pea/bean (legume) family,
therefore you wouldn’t sow before peas & beans. But it can replace in a crop rotation plan and will add nitrogen to the soil which will be beneficial to the next crop of leafy brassica’s
- There are green manures that don’t need to follow a crop rotation plan such as:
Buckwheat Forage Rye Phacelia
These types of green manure would be used primarily to add organic matter to the soil, whilst also offering the benefit of weed suppression.
If you want more advice about what to sow in different soil types, then we have an easy to follow summary guide which shows which green manure variety to sow based on your soil requirements, you can find it [here]
The start point, regardless of soil type, is that the soil is going to have to be dug over and free from weeds
- You then need to know what type of soil you have. Certain green manures are used in specific soils only and if you want to get the maximum nitrogen/soil benefit then you need to match the green manure with the right soil, for example, Lupins would be used in acid soils, whereas Alfalfa is not suitable for acid soil but loves dry soil
- Watch Monty Don sow Forage Rye to help get to grips with his own clay soil problem [click here]
- It’s not always necessary to sow based on specific soil, certain green manures such as Italian Rye will suit most soils and will act purely as a soil improver by increasing the organic matter
3. Time of year
- Green manure is thought of as mainly an autumn/winter crop due to its ability to assist in reducing the impact of soil erosion from the winter rains and allowing the roots to grow deeper into the soil to assist with aeration and breaking up heavy soils such as clay. However, they also offer similar benefits in summer months, with the leafy foliage acting as a defence against the drying effects of sun and wind. They truly are an all-year-round beneficial plant
- Green manure crops can be part of a garden crop rotation, growing in a planting bed or allotment for a full season. A good home garden/allotment green manure strategy is to use green manure crops as catch crops. A catch crop is a filler crop; it grows in a vacant spot before or after a main crop. A catch crop can be interplanted with your main crops.
- The time of year needs to be taken in to account depending on your needs, for example, you may want a quick annual cover crop such as Fenugreek, which takes less than 10 weeks from sowing to digging in, or alternatively, cut down and left on the soil as mulch or composted. Sow spring green manures as soon as the soil can be worked in spring. Spring green manures can grow for 6 to 10 weeks before main crops are planted.
Or you may wish to sow a long-term crop like White Clover for over-wintering
- Over-wintering.... winter green manures can be sown as soon as the summer harvest comes out of the ground. When possible sow the winter green manure at least 6 weeks ahead of the first killing frost. Typically, green manure is sown in autumn so that they will help to prevent the nutrients in the soil being washed away with the winter rains and have sufficient time for the root system to develop to help open-up heavy soils. They maybe legumes such as Winter Tares (vetch) or non-legumes such as Forage Rye both of which are hardy green manures that will grow throughout winter before being dug into the soil in spring.
If sowing in clay soil, one option is to incorporate the green manure ahead of winter so that the frosts can help to break the soil down.
- Green Manures can also be used as an interplanting-crop, or catch crop. Main season green manure crops serve as a living mulch to keep down weeds and slow soil moisture erosion. Sow main season green manures as an under crop - that is, wait for 3 to 4 weeks after sowing your main crop then sow the green manure as an underplanting. Yellow Trefoil, for example, is a low grower that can be sown in between taller crops that have open canopies like tomatoes, potatoes, sweetcorn & especially long-standing brassicas which overwinter. Dig in after harvests, or leave to over-winter to help suppress weeds.
- Full season green manure: can be planted as part of crop rotation for a full season. A full-season green manure crop will knock down most perennial weeds and will reduce pest root populations. Full-season green manures can also feed the soil. Put full-season green manures in your four-year crop rotation plan.
The good news is that whenever you need to sow, there is a green manure solution. Our summary guide helps you make the right choice based on your timing requirements, you can read it [here]
4. How to sow
Sowing green manure is easy. Here are the steps:
- Prepare the soil by digging it over and removing any weeds, break up any clumps, rake the seedbed evenly to a fine tilth and then lightly tread the soil
Rekha preparing for Green Manure
- Determine the square feet/metres that you intend to sow
- For small green manure seeds broadcast sow the green manure (e.g. scatter evenly) this ensures you get good coverage for weed suppression. Larger green manure seeds such as Field Beans and Forage Peas can be sown in furrows 10cm apart in rows 20cm apart to a depth of 5cm
- Rake over the seedbed and water well
- Keep the seedbed just moist until the cover crop germinates and becomes established. If the weather is very hot keep the seedbed from drying out by sprinkling straw over the seedbed. If birds start digging up the seed, lay a loose spun poly row cover over the planting bed.
For a fuller explanation on how to sow green manure, you can read our guide [here]
5. Digging in
The 4 steps of digging in:
- Green manure should be cut down before flowering when the stems are soft and ‘green’
- Dig the green manure into the top 15cm of soil
- Or alternatively, the green manure can be left on top of the soil as a mulch and let the worms drag down the organic matter
- Wait 30 days before sowing the next crop
- Chop up top growth (foliage) into smaller pieces, use the edge of a spade but you can also use shears especially if the foliage is too coarse or long. Turnover and dig in foliage and green manure roots with a spade into the soil to a depth of 15cm. Do small areas at a time. Gently tamp down the soil with the back of a rake and then rake the soil to a fine tilth.
- Foliage can be removed or composted if it is too coarse or too hard to dig in or if you just prefer to. Then either dig in roots by turning over in a small section or if you wish to leave in situ and plant seedlings through roots. This last method is only suitable for annual types that die off once very closely topped, perennial green manures like clovers will continue to grow.
- Leave 4 weeks before sowing seed especially with green manures like Forage Rye and Winter Tares as they have a chemical that once released inhibits the germination of small seeds – great against weed seed germination but not so for veg seeds. However small plants/seedlings are not affected and can be transplanted within a couple of weeks.
- It is best to dig in or top green manures before they start flowering and especially before they go to seed. The stems become woody and they are harder to break down in the soil. However you may wish to allow a few to flower especially the Clovers or Phacelia as their flowers are havens for bees & beneficial insects – they will just need careful management to ensure they do not go to seed unless you wish them to.
- And for those who follow a 'No dig' approach...same method involved in cutting down the green manure, but instead of digging in just leave the cuttings on the surface and it will act as a mulch, or hoe in. Otherwise, the cuttings can be removed and simply composted.
After all that hard work you can now be confident that you and your soil will reap many benefits from incorporating green manure into your crop rotation plans...
- Organic matter – lots of leafy green manure vegetation helps to increase the organic matter in the soil. Better than horse manure – that you don’t know where it's come from and what's in it
- Nitrogen – green manure can either add nitrogen to the soil or it can lift the nitrogen closer to the surface, thereby super boosting crop growth
- Leaching – using green manure over winter prevents the rain from washing the soil's nutrients away
- Pests – green manure provides cover for frogs, beetles and other natural predators that feed on pests such as snails and slugs. Also helps deter some of the crop pests, for example using a low growing green manure to deter carrot fly or mustard to help combat wireworm in a potato crop
- Weeding – anything that reduces the need to weed has to be a good thing. Well, green manure does just that. Does away with the need for artificial weed barriers, harmful chemicals, and dodgy horse manure!
Welcome to the world of Green Manure...a truly super plant in your vegetable plot or vegetable garden...create beautiful soil, naturally.
#greenmanure #GYO #growyourown #nomorebaresoil