Green crops are also known as cover crops or manure crops and are grown for the nutrients and organic matter that they give back to the soil. This is a natural method of soil maintenance that will boost and replace nutrients and encourage earthworms and other micro-organisms. These crops are also a way of adding rich organic matter to the soil and helping to stop the soil compacting during winter. Most people plant green crops in early autumn to replenish the garden for spring planting.

The most common types of green crops are: 

• Blue Lupin – a quick growing, nitrogen fixing crop suited to cooler climates.
• Barley – adds protein, nitrogen and organic matter to strengthen the soil structure.
• Oats – used to combat soil erosion and to help break up hard clay soils.
• Mixed grain – adds nitrogen and organic matter to the soil as well as helping to prevent wire worm.
• Mustard – cleans up harmful soil fungi and provides good control of  wireworm and nematodes, which often ruin root crops such as potatoes and carrots. Mustard is a good weed suppressant suited to cooler climates but do not use this crop if you are planting cauliflower, broccoli and other brassica in the same area the next season.
• Broad beans – return nitrogen and organic matter to the soil.
• Peas – add nitrogen to the soil and are incredibly useful for making pea straw for mulching in spring.

Plant the green crop when it is raining because it is essential the seed does not dry out when germinating. You know the crop is ready to be dug into the soil when it flowers in late winter-early spring, but note that the stems should still be soft and watery. Chop the foliage off near the ground and dig it into the first 15cm of soil. An alternative method is to leave the foliage on the garden and then cover it with a layer of compost. By adding Blood & Bone Fertiliser or animal manure you will speed up the breakdown of the crop, but wait at least three weeks after digging in the crop before planting the next crop of spring vegetables.

Whichever green crop you choose they are a good cheap way to add organic nutrients to your soil.