Improving your soil is about replacing the nutrients your plants consumed during the growing season, and adding organic matter to improve the structure. From well-rotted manure and bags of specialist compost to leaf mould and rock dust, here are some of the most effective ways to replenish the soil in your garden ready for the year ahead.
When to feed your soil
Autumn is the traditional time to think about soil replenishment and adding compost is the most common way to achieve it. Aim to spread approximately half a wheelbarrow load of quality product per square metre, then roll up your sleeves and dig it into the soil. During the winter, worms will feed on the compost, dragging it deeper into the ground and incorporating it into the soil for you.
Compost works by encouraging soil particles to clump together to form what are called ‘soil aggregates’. This helps soil to develop a good structure, by which we mean, it drains better, holds more water without becoming sodden, and is less susceptible to erosion from the elements. Nutrients in the compost are also distributed throughout the soil, making it more fertile.
Any ruminant animal dung makes good fertiliser but they do vary in nutrient composition so check that you’re buying what your soil needs. Chicken manure is also a great option with a high concentration of nitrogen – buy this in pellet form and spread it thinly in accordance with the manufacturer’s instructions.
If you like to use manure, make sure it’s well-rotted. It takes at least three to four months to make manure safe, but composting it for at least six months is better. The composting process is essential for breaking the material down and for killing off pathogens that might make you ill.
Fresh dung also contains ammonia which, as well as smelling nasty, can ‘burn’ plants. Applying manure to your garden before it’s had time to break down encourages flies and isn’t very good for your plants either, tending to make them leggy and overly foliferous at the expense of productivity.
Non-animal derived compost
Compost takes many forms including mushroom compost, leaf mould and your own kitchen compost. If you’re buying it for bulk application rather than for planting seeds or topping up containers, it’s a good idea to find out if your local council can supply it from their municipal green waste composting service.
Council compost ‘heaps’ often get much hotter than domestic compost so are more likely to kill off any nasty bugs than your own, cooler, garden bin. However it can sometimes contain plastic and twigs. Check for compost filtered to 20mm that complies with the UK’s Compost Certification Scheme.
The term ‘green manure’ refers to quick-growing plants sown during the autumn and winter months, which you cut down while they’re still green and then dig into the soil during the spring. This class of soil improver nourishes the soil, protects it from erosion during heavy rain, and helps to keep weeds under control.
Mustard leaves and ryes scavenge for soil nutrients via their root systems 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, preferably in autumn after you have lifted your vegetables.
A note of warning: Don’t let these plants run to seed before you cut them back and dig them into the soil or you’ll have a weeding headache to contend with.
Legumes (clovers, peas and beans) also make great green manure. These plants have nodules on their roots housing bacteria which 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.
Crops like 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.
Made from crushed volcanic rock which is particularly high in minerals, when you add a bag of rock dust to the soil, the natural weathering process releases minerals and trace elements throughout the growing season. Using this fertilisation technique is not only effective, it also helps the fight against climate change because the calcium and magnesium in the dust converts atmospheric carbon into carbonates and locks them away in the soil.
Autumn is the time to put back the nutrients your summer crops absorbed from the soil as they grew and ripened. Part of the annual gardening cycle, it’s good gardening and helps make sure your soil is in tip top condition ready to give your spring sowings the best of starts.
Lead image: Ericaceous Compost from Suttons