Know Your Dirt
Soil is generally rated by its fertility and texture. Fertility depends on essential nutrients, such as nitrogen and phosphorus, and a pH that makes these nutrients available to plants. Texture refers to the size of the soil particles and their cohesiveness. You can check the quality of your soil - some garden centres will do this for you - but a quick way to get an idea is to look at your plants health. If they're doing well then chances are your soil is doing a good job, but if they're looking sickly, yellowing or need a lot of feeding, then maybe your soil needs testing. And if you are worried about chemical pollutants, avoid the use of inorganic fertilisers, and artificial pesticides or fungicides.

Soil Improvers
If the pH is unbalanced then you can add things like lime to raise alkalinity or sulphur to raise acidity. (This needs to be done slowly so that you don't shock the plants though.) If you need to add nutrients then if you can you should use organic fertilisers such as composted vegetation, composted animal manure or green manure. Organic material is the best thing to add because it helps the fertility and texture of the soil at the same time. Decaying organic matter releases nutrients over a period of time, helps sandy soil by retaining water and corrects clay soil by making it looser and allowing air water and roots to move around. It also encourages microbial activity and provides nutritional benefits.

Dump the Chemicals
Chemical pesticides and fungicides may help your flowers look good but they can easily enter the food chain, killing everything from vital worms and bees up to frogs or even hedgehogs. Chemicals can also spread through water, polluting ponds, killing fish and affecting plants a long way from the spot they were used. So if you have to fight slugs and other unfriendly critters, look for natural alternatives if possible, replacing slug pellets with nematode worms, for instance.

Planting Suggestions
If you want to improve the quality of your soil you could try growing green manure. These are crops grown on unused soil which are then tilled and allowed to decompose in the ground. While they grow their roots help keep the soil loose and the plants themselves help suppress weeds. Good examples of green manure are lupins, Italian rye grass or buckwheat. Plants such as clover and vetch also add nitrogen to the soil.

Get Inspiration
Get tips on soil improvement from the Soil Association, and from Alan Titchmarsh at Crocus.