The next few months are a really good time to think about putting the nutrients back into soil that have been used up over the past growing season.
The traditional way of doing this is by incorporating manure or compost. Use about half a wheel barrow per square metre and dig in. The worm activity over the winter will help to pull it in deeper. If using manure then make sure it’s not too fresh – apart from the smell, fresh manure releases ammonia which will damage or kill plants. Make sure that any you use has been left to rot down for at least 6 months. Compost can take many forms; mushroom compost, leaf mould, your own garden compost or why not see if your local council can bulk supply. It’s often available from your local recycling centre although reports vary about the quality. Council compost ‘heaps’ frequently get much hotter than domestic compost so are more likely to kill off any ‘nasties’ than your own cooler garden bin but we have had reports that it’s often full of plastic and twigs – so best to check it out before you order bags and bags of the stuff!
However if you don’t fancy all that digging in then Green Manure may be the crop for you. Fulfilling a number of purposes, green manure covers a range of crops from mustards and ryes to peas and beans (legumes) all of which will not only put nutrients back into the soil, but will also act as cover crops, preventing soil erosion and run off during heavy rain and also stopping weeds from taking hold.
Mustards and ryes scavenge for soil nutrients via their good root system and this is then released into the soil when the crop is dug in and decomposes. It’s extremely easy to grow – simply rake over the soil to loosen the top and scatter the seed and rake again. Make sure it’s well watered in. You can use at any time that you have an empty space for at least 6 weeks but are normally sown in autumn after you have lifted your vegetables. Watch carefully as it needs to dug in before it starts to set seed. Depending on weather conditions this may not be until early spring but if the weather is very mild then you may have to do it a lot sooner. Leave for at least 2 weeks before sowing a new crop.
The legume group (clovers, peas and beans) have swellings on their roots (nodules) that house bacteria that are able to incorporate atmospheric nitrogen (as well as phosphate and potassium) into proteins. The bacteria ‘harvests’ the nutrients and gives it to the plants in exchange for sugars etc. Crops such as broad beans and runner beans (but not french beans, which do not nodulate well in the UK) can be cut down at the end of harvest and their roots dug in to release the nitrogen over winter. In addition legume flowering plants such as lupins, sweet peas and brooms also nodulate well and can enrich the soil.
Another new and usual way of adding nutrients to the soil is to use Rockdust. It’s made from volcanic rock which is particularly high in minerals; the crushed rock is added to the soil and the natural weathering process releases minerals and trace elements throughout the growing season. The use of rock dust is championed by Scottish couple Cameron and Moira Thomson who have used it to convert their six acres of infertile land into soils capable of producing cabbages the size of footballs, onions bigger than coconuts and gooseberries as big as plums. They also assert that their technique can also help the fight against climate change as the calcium and magnesium in the dust converts atmospheric carbon into carbonates. There is more about rock dust in this article in The Independent.