Cover Crops Growing Guide

Cover crops, also sometimes called green manures, are plants you grow not to eat, but to improve your soil. They’re quick to grow, inexpensive and a natural way to replace nutrients that summer crops have used up.

Most gardeners sow cover crops in autumn after harvesting, especially in beds that won’t be used over winter.

Why cover crops are so useful

Cover crops do a lot of jobs at once:

• Replace nutrients: As they grow, they pull nutrients from deep in the soil. When you dig them in, those nutrients become available for your next crops.
• Add organic matter: When the plants break down, they feed the soil and help it become more crumbly and easier to work with.
• Support soil life: The roots and decaying plant material feed microbes, worms and fungi - all the things that make soil healthy.
• Reduce weeds: A thick cover crop blocks sunlight, stopping winter weeds from taking over.
• Protect soil from weather: Rain and wind can wash nutrients away over winter. Cover crops act like a blanket, holding everything in place and helping prevent erosion.

Which cover crops to grow

Two of the most popular options are mustard and lupin. They each bring something slightly different:

• Lupins: Add organic matter and fix nitrogen - meaning they naturally add nitrogen to the soil, which is great for leafy greens and other hungry crops.
• Mustard: Adds organic matter and can help reduce soil pests like wireworm, which often attacks root crops such as carrots and potatoes.

A good mix is three parts lupin seed to one part mustard seed. This gives you the benefits of both. Other cover crops include oats, phacilia and chicory.

When and how to plant cover crops

• Sow in autumn once your summer crops are finished.
• Scatter the seed over the bed, rake it in lightly, and water well.
• Let the cover crop grow through winter. It will protect the soil while you take a break from gardening.

When to ‘chop and drop’ your cover crops

When digging your cover crops in, timing matters. To get the most benefit:

• Cut down and dig the cover crop into the soil before it starts to flower, usually in late winter or early spring.
• Aim to do this when the stems are still green and soft, not woody.
• Try to incorporate it before the plants reach about 50 cm tall.
• Do this 4–6 weeks before you want to plant your next crop, so the plant material has time to break down.
• For example, if you want to plant tomatoes in mid October, dig in your cover crop around early September. After digging it in, leave the soil to rest so the organic matter can decompose and release nutrients.

Tip! ‘Chop & drop’ your cover crop using a weed eater, hedge shears or similar.

Extra ways to boost your soil

Alongside cover crops you can add other gentle soil conditioners to support the breakdown process and improve fertility:

• Gypsum or Tui Lime helps the plant material and organic matter break down faster.
• Tui Sheep Pellets or Tui Blood & Bone complement what your cover crops provide and add extra nutrients.