Cover crops, or green manures, are a great way to protect ground that would otherwise lie bare over winter. Dig them in and they’ll help to build up your soil’s organic matter – which is great news for the vegetables that follow! The end of summer is the perfect time to sow a cover crop for winter. Read on or watch our video to discover exactly how to do it.
Why Grow Cover Crops?
Cover crops are plants grown to protect or improve the ground for future crops. Keeping soil covered over winter protects it from erosion and helps support all the beneficial life associated with it. It also gives weeds less opportunity to establish, meaning cleaner beds for sowing or planting in spring. Dig the cover crop into the ground at the end of winter and it will rot down to add valuable organic matter, helping to feed the plants that follow.
Which Cover Crops to Grow
Cover crops with deep or fibrous roots such as cereal rye help to improve soil structure by breaking it up. Others, like mustard, grow very fast to produce lots of lush foliage that can be incorporated into the soil after just a few months to boost its organic content. Mustard is a particularly good cover crop for clay soil, where it can be dug in before winter so frosts have a chance to break the soil up. Prolific salads such as mache or corn salad may also be grown this way.
Poor Soil / Hungry Crops
Some cover crops directly add nutrients to the soil by fixing nitrogen at their roots. Examples include winter field beans and peas, clover and vetch. These are all types of legume and are a great choice for sowing before nitrogen-hungry brassicas such as cabbage.
Phacelia can be sown in late summer in milder areas – or wait until spring if winters are cold where you are. Phacelia is very good at suppressing weeds and will improve your soil’s structure. The flowers are stunning and a major draw for bees and hoverflies, so consider leaving a small patch to flower to attract them. Buckwheat is another good example, offering numerous benefits for weed suppression, soil enrichment, and as a source of nectar for beneficial insects in spring.
Check the planting times in our Garden Planner to pick the right cover crop sowing time for your area.
How to Sow a Cover Crop
To sow a cover crop, start by roughly digging the ground over. Remove all weeds, especially perennial ones. Tamp down the soil with the back of a rake then scatter, or broadcast, your seeds evenly across the soil surface. Don’t sow them too thickly. Rake the seeds into the soil, tamp down with the back of your rake, then water the ground if it’s dry.
The chunky seeds of winter field beans may also be sown in rows. Use a spade or hoe to dig out trenches about two inches (5cm) deep. Space the trenches eight inches (20cm) apart. Now sow them so they’re around four inches (10cm) apart then fill in the trenches to cover them.
Digging in a Cover Crop
In most cases it’s best to dig your cover crop into the soil before it begins to flower, perhaps leaving a few for early beneficial insects. At this stage the stems will still be soft, making them easier to cut up and dig in, and quicker to rot down. Incorporate the foliage into the soil or simply cut it off and leave it on the surface as a mulch for the worms to dig in for you, covering it over with cardboard if you’re concerned about weeds springing up. Cover crops should be dug in at least one month before sowing or planting so they have enough time to begin decomposing.