Growing Cover Crops will Improve Your Soil
Adding organic matter to your soil is one sure way to improve the soil, encourage earthworms, provide plants with more nutrients, provide better growing conditions and harvest tastier, healthier food for yourself and your family to enjoy.
Green manure is created by leaving uprooted or mown crops to wither on a field so that they serve as a mulch and soil amendment. The plants used for green manure are often cover crops grown primarily for this purpose. Typically, they are dug or plowed under and incorporated into the soil while green, prior to full flowering can occur. Green manure can play an important role in sustainable annual cropping systems either on a large scale or in your own backyard food garden.
There are many ways you can add organic matter, and an easy one is to allow nature to add it for you. By planting a green manure crop, you will be adding nutrients to the soil, as well as out-competing potential weed species in the down-time and fallow months in your garden. A green manure crop is simply a crop grown in order to be cut down and dug in after the peak of its growing season. The best time to cut down your green manure crop is just as the first flower buds appear, the plant will be almost at its peak size and you will get the maximum amount of bio-mass from it, without it draining its resources into producing fruit. Generally, you don’t want to allow your green manure crop to flower as all the energy and nutrients from the plants will go into the flowering and you want those nutrients put back into your soil.
There are a variety of plants you can use as a green manure, and what you choose to use will depend in part on what climate you are growing in, as well as what you anticipate you will grow in the soil after the green manure crop has been dug in. For example, legumes, such as peas or beans, which fix nitrogen in the soil are a great green manure crop to grow prior to planting lettuces, kale, bok choy, coriander and other leafy greens – they will thrive because of the additional nitrogen which has been provided by the leguminous green manure crop.
Legumes are generally a fairly easy to grow green manure crop and can be used all year round or seasonally to add bio-mass to your soil. Legumes are generally lower in carbon and higher in nitrogen than grasses. This lower C:N ratio results in faster breakdown of legume residues.
For a winter cover crop you can grow annuals such as crimson clover, peas, broad beans, hairy vetch or subterranean clover. Make sure you prepare the bed well with a light tilling to open the soil up a little before planting. Start your planting after you have had two or three good rains in Autumn/Fall which will make the soil damp enough to encourage the seed to sprout. Add the seeds and cover them over. If you live in an area of winter rains, the seeds will be sprouting soon enough, depending on how much warmth is left in your soil – the warmer the soil, the sooner they will sprout, so don’t leave it too far into the winter season to get your seed in the ground. Left to its own devices a winter annual crop can be ready to cut and turn in within 12 or so weeks – the longer you leave it the more bio-mass you will have, however don’t leave it beyond flowering as the nutrients in the plant will be lost through the flowering process and won’t be available to go back into your soil. I grow a winter annual cover crop in my vegetable garden and get it back into the ground quickly prior to my spring planting.
Planting legumes as a cover crop will:
• Fix atmospheric nitrogen (N) for use by subsequent crops (follow your legumes with leafy greens – they will love it!)
• Reduce or prevent erosion
• Produce biomass and add organic matter to the soil
• Attract beneficial insects
• Reduce weeds
Perennials like white clover or red clover can be grown year round and biennial legumes like sweet clover make great cover under longer term plantings such as in your orchard. If you choose a perennial or biennial crop, then you will simply need to leave it longer before you cut it into your soil. These are both great in an area where you are growing fruit trees as you will disturb the soil less often and can simply cut the green manure down once a year, leaving it as mulch for your fruit trees, providing them with some protection through the summer months and helping the soil to retain moisture for longer.
Brassicas and Mustard plants are not only great for quick growth, they also emit chemicals as they grow which may be toxic to soil borne pathogens and pests, such as nematodes, fungi and some weeds. The mustards usually have higher concentrations of these chemicals. They are great to put in the potato patch after you have harvested your vegetables and are also great around fruit trees to prevent soil based diseases. If you are keen to keep your soil clean, then consider growing cauliflower, broccoli, kale, cabbage, turnips in your rotation after potatoes. Most of these have long tap roots too, so will help to reduce soil compaction when the soil is moist and easier to penetrate. My experience is that I get a lot less white cabbage moth in the cooler months too, so the manual pest control I have to do is a lot less than if I grow these vegetables in winter.
Mustard is a term that is applied to many different botanical species, including white or yellow mustard (Sinapis alba, sometimes referred to as Brassica hirta), brown or Indian mustard (Brassica juncea) and black mustard (B. nigra (L.). Mustards are easily grown in summer or winter areas where the risk of freezing is low. Once planted, you should have a crop ready to turn in, in around 6 weeks. Cut the crop in and water the area – this will help to release the glucosinilates ( a naturally occurring pungent substance) which are key to bio-fumigation. Plant the seeds 1-2 inches deep in the soil and grow them as a monoculture in a specific area of your garden. Make sure animals such as cattle, horses or pigs can’t get access to them as they will make them sick. Chickens on the other hand love them!
Using Bio-Mustard and Brassicas as a cover crop will:
• Prevent erosion
• Suppress weeds and soilborne pests
• Alleviate soil compaction
• Scavenge nutrients
• Act as a biofumigant – cleaning your soil
Lucerne, also known as alfalfa, is a perennial which makes a great cover crop. It is a cool-season perennial commonly grown for feeding livestock but also makes a great cover crop and soil conditioner. Being drought tolerant and the long deep roots will help to minimise soil compaction and draw nutrients up from a long way down in your soil structure. Lucerne is a natural source of nitrogen. It’s ideal for improving the soil and providing erosion control. When growing alfalfa, choose an area with plenty of full sun and good drainage as it doesn’t like wet feet. Also look for an area with a pH level between 6.8 and 7.5. Plant seeds about a half inch (10mm) deep. Simply sprinkle the seeds evenly onto the soil and cover lightly with dirt. Use about 50gm of seeds per square meter and space rows about 50cm apart.
You should begin to see sprouts within 7-10 days. You can keep them growing for as long as you like – the longer they grow, the longer those deep tap roots will grow! You can also cut it down several times a year and it will come back. It is a great crop to grow as an understorey in your orchard, where you will not want to be continuously disturbing the soil. Once cut, you can feed it to your livestock or leave it as mulch for the trees.
Using Lucerne/Alfalfa as a cover crop will:
• Prevent erosion
• Suppress weeds
• Encourage bio-drilling – alleviating soil compaction
• Attract beneficial insects during flowering
• Produce biomass
• Add organic matter to the soil
• Fix nitrogen in the soil
Using a combination of cover crops in different situations will provide your soil with increased bio-mass and improved nutrition availability for your plants, whether they are annuals or perennials. You can also plant a mix of cover crops in one bed; this will give you multiple benefits of different varieties. The exception to this is the brassicas – they are better planted on their own, because of their fumigation ability.
Cover crops will encourage soil working earthworms to aerate and fertilise your soil, giving your plants the best chance of producing delicious, nutritious food for you and your family. Colourful cover crops such as bachelor’s buttons and crimson clover will not only improve soil, they'll beautify your garden beds. Why not try a cover crop this season in that spare space you have – the very least it will do is supress the weeds and provide mulch and bio-mass for next season.
For great advice on getting started in your garden, or for tips on how to improve your vegetable yield, this book is a great thought provoker to help you think about how you can get more from your garden, without spending all your pay!