Green Manure: Optimise Your Soil This Year

Written by Betty Green

Food crops need several nutrients in relatively large quantities during the vegetative or growth period, especially nitrogen

To grow healthy, tasty vegetables, getting nutrients into the soil before planting is critical. Food crops need several nutrients in relatively large quantities during the vegetative or growth period, especially nitrogen.

Unless your soil is regularly replenished with nutrients, it can quickly become barren and unyielding. Digging in organic matter or compost will help readdress the balance. Another option is green manure.

Try growing vetch throughout the winter underneath blackcurrant bushes. Then, hoe the vetch off in the spring and leave the foliage to decompose. The blackcurrant bush will take up the extra nitrogen when it needs it most.

Green manures are plants that are specifically grown to benefit the soil. They do this in several ways:

• By adding valuable nitrogen

• By improving drainage and water retention

• By repressing weeds

• By enticing advantageous insects and predators

Low-growing green manure like trefoil is excellent for covering the bare ground between rows of tall crops like sweetcorn and avoiding weed growth.

Green manure plants are quick growers, meaning the soil can benefit from green manure just a few weeks after sowing.

How It Works

Nitrogen Fixing

The roots of green manure plants run deeper than other crops grown in the garden, so they can source nutrients from a vast area. Plants hailing from the legume family, such as clover, alfalfa, soybean, peanut and rooibos, absorb nitrogen from the atmosphere and fix it into their roots.

Legumes have symbiotic rhizobia bacteria living within their roots. The bacteria produce nitrogen compounds and store them in nodules on the roots, which are then used to grow the plant. In return for nitrogen, the plant supplies the bacteria with photosynthesis-derived sugars and other nutritional elements to keep them alive.

Once a green manure plant hits maturity, dig it back into the soil to allow its nutrients to return to the earth so crops can take advantage. This nitrogen influx also helps provide for the soil’s microbial life, increasing its health tenfold and creating a healthy and rich growing medium. Those following no-dig techniques can still work with green manure. Instead of digging in, leave the cuttings on the surface to act as a mulch or hoe it in.

Improved Soil Structure

Green manures can help correct any problems with soil structure, whether too heavy and clay-like or too sandy and delicate. The green manure has a broad and deep burrowing root mass and can aerate dense soils for better drainage. In addition, the roots bind to the soil particles in light, sandy soil, acting as a sponge to soak up nutrients.

Weed Suppression

Nature rapidly occupies bare soil, generally in the form of weeds. A cover crop of quick-growing green manure, like mustard, will snuff out any pockets of rebel weeds, saving you a lot of work in the garden. White clover is a great long term cover crop, eventually suffocating the weeds and building up precious nitrogen stores in the soil.

Pest Control

The bright flowers of crimson clover or blue tansy attract bees and hoverflies, both of which are excellent weapons against aphids! Research shows that some flying pests can become confused and deterred if they cannot recognise the outlines of their food plant. Try planting brassica with trefoil or vetch to conceal the silhouette of the crop and prevent cabbage root fly. Slug predators like beetles and frogs love the damp environment of a green manure cover crop.

Practical Ways To Use Green Manure

If you have inherited overworked soil in a new garden or allotment, try growing only green manure for the first season. Although you will have to wait longer for your veggie crops, when you do start growing, your soil will be much healthier and reward you with a much better yield.

You can sow some green manure crops in autumn to keep the soil covered during winter. Grazing rye or winter vetch will fit the bill perfectly. Then, once spring is on the way and the air warms up, dig the crops into your soil to get the media teeming with nutrients in anticipation of your summer veg haul.

Green manures can be used as catch crops, which are quick-growing plants that can be sown between seasons to use soil that would otherwise be standing empty. Try planting green manure after harvesting crops like potatoes; mustard is a good option.

BIO Betty Green has two passions in life: plants and food, which is perfect considering the two go hand in hand. Betty is a dedicated gardener and self-taught cook who is big on organic produce and sustainability. With a large family of four children to feed, she has been slowly increasing her portfolio of garden produce for her growing repertoire of delicious recipes. Betty loves writing about plants, cooking, and sustainability.