Improving the soil involves two aspects - firstly adding more nutrients and secondly adding humus (organic material like garden compost or manure) to improve the structure.
Adding organic material makes the soil airier and this aids root development and tends to improve drainage on heavy soil. Once the organic material breaks down, after a year or so, the process may need repeating.
The main consideration is your soil. Those on heavy clay may wish to follow the Great Dixter method of adding coarse grit to heavy clay to improve drainage.
Adding grit has the advantage of being permanent and clay is already a fertile medium. Once the digging is done it would then be possible to top dress with a sprinkling of a slow-release fertiliser like blood, fish and bone every March and September.
Related: improving clay soil.
Many plants, including most silvers and tap-rooted plants like eryngiums and verbascums, prefer a poorer diet. So soil improving needs to be targeted in certain areas - where vegetables are to be grown, or where moisture-loving plants like phlox are to be planted.
Make your own compost heap
Making your own compost heap is the first step to good soil, within six months you will have your own free, friable soil improver. Making your own compost can provide a great source of nutrients for your garden as well as using up leftover food and garden waste.
Related: guide to making a compost heap.
Double digging (for manure and compost)
Double digging involves removing one spit (or a spade's depth) of soil. The bottom of the trench is then roughly dug over with a fork to break it up to improve drainage.
At this stage garden compost or manure can be incorporated into the trench and covered with the remaining soil to make a raised fertile mound. This is perfect for legumes (like peas and beans) and you can even fill one of these trenches with vegetable waste and leave it over winter.
Buying in manure
Animal manure can be a problem
I am old enough to remember that when a horse went down a London street everyone would rush out with a bucket and shovel to collect the precious muck.
One horse apparently produces between 1600 and 1800 pounds per year and in Susan Campbell’s The History of Kitchen Gardening she describes the perfect diet for a horse kept for its manure. It’s quite a thought. But these days most horses are bedded out on woodchippings rather than straw and this makes their manure less user friendly.
A modern problem - aminopyralid
Animal manure has caused great problems for gardeners because some batches have contained a chemical that kills crops and many gardeners have had problems over the few years.
The problem has been linked to a new herbicide called aminopyralid (a hormone weed killer) being used on grassland by the farmers. The animals either feed on the grass, or ingest silage during the winter months.
The residues come out in the manure. The most sensitive crops affected are tomatoes, peas, beans, carrots, potatoes and lettuce.
Many farmers now buy in fodder and they may not know whether it’s been treated or not. But manure from cows and horses, once so valued by the vegetable gardener, is now to be viewed cautiously. For this reason I have stopped buying in manure, but it has made my compost heaps even more necessary.
Apparently a good way to tell if the manure is fine is to buy a tomato plant and repot it using some of the manure.
Related: planting green manure.
Green garden waste
Councils all across the country now have green waste collection schemes and they sell their compost. Schemes vary because many councils sell it straight to a commercial compost company. Others seem to sell their own.
Ring you council offices to find out their system. If you can buy it cheaply you will be able to dig this straight in without fear of unwanted seedlings.
Mulching is double-edged sword when it comes to improving the soil because the decomposition process uses up nitrogen on the soil surface - robbing the ground of nutrients.
The way round this is to use a nitrogen feed (like chicken pellets or powdered 6X chicken manure) before you apply your mulch of bark.
The other golden rule is to always mulch wet, warm soil to trap moisture. Mulching on dry soil prevents rain penetrating the ground.
Related: mulching to save moisture.
Feeding your soil
Slow-release fertilisers are much better at releasing nutrients in the best way. Blood, fish and bone is generally the best and the powder is easy to spread.
There are water-based fertilisers that deliver a fast rush of nitrogen and they promote a lot of soft leaf. This soft growth is unattractive to look at and more prone to pets attack - it’s almost a gourmet meal for aphids. It could be used on brassicas, but isn’t suitable for strawberries in flower.
If you want to promote flower and fruit opt for a tomato feed or make your own comfrey tea.
Related: making your own comfrey tea.