Improving your soil

If your soil scored 20+ in the visual soil assessment, don't be complacent as it can deteriorate if you don't look after it. The following advice on improving soil also applies to maintaining it's good condition.

Improving heavy soil (high clay content)

• Add organic matter regularly. Fork compost into the top 15-20cm of the vegetable garden and annual beds each time you plant. Mulch garden beds in spring and top up over summer. Home-made compost, mushroom compost and bagged compost from a garden centre are all suitable. If using sawdust or wood chips (both from untreated wood), sprinkle fertiliser containing nitrogen on the soil first to avoid depleting soil nitrogen reserves as the woody material decomposes.
• Use bulky manures such as sheep pellets or animal manures. It's a good idea to mix them in the soil as they can get hard and crusty on the surface if they dry out, and some types smell.
• Grow green manure crops such as ryegrass, oats, mustard, barley or lupins. Sow in autumn, cut them down in early spring and dig in.
• Drain the soil if waterlogging is a problem. Also, prevent run-off going into the garden.
• Stay off the soil when it's soaking wet. Don't dig or cultivate when very wet or very dry.
• Start a new patch: In cold areas dig the soil in autumn, leaving it in rough chunks for frost and rain to break down. In warm areas dig in spring or early summer, break it down with a fork and mix in organic matter. From then on, in all areas, try to cover bare soil with mulch to protect it from the pounding of heavy rain that can cause a hard surface crust later when it dries out.
• Apply lime or gypsum. See Sweet and sour.
• Alternatively, avoid planting in the soil altogether.
  Build raised beds up to 50cm high for trees and shrubs, 15-30cm for annuals and vegetables (see our article on Growing vegetables for more on raised beds). Fill with enough bought-in good-quality topsoil, a garden mix such as Living Earth or Dalton's Garden Mix, or a topsoil/garden mix combination. You can plant directly into this. Earthworms and soil micro-organisms will eventually combine it with the upper layer of soil, and plant roots will grow down into it. This is an expensive solution but allows you to establish a garden relatively quickly. Some garden mixes dry out quickly, so need regular watering in summer. A layer of newspaper under the mix helps kill off existing weeds.
• Mix coarse sand or pumice into the top 15cm or so of soil.

Improving light soil (high sand content)

• Again add lots of organic matter, both mixed in and as a mulch, to conserve moisture - sandy soils dry out rapidly.
• Where practicable add silt and clay by mixing with bought-in topsoil.
• Use bulky animal manures (as already mentioned in the section for improving heavy soils).
• Nutrients wash out of sandy soils readily so you may need to feed them to get good growth. Use fertilisers of organic origin (they release their nutrients relatively slowly) or slow-release types. Or apply soluble fertilisers little and often. But be aware that constant use of highly soluble fertilisers may discourage soil organism and biological activity.
• Grow green manure crops but make sure to dig them in while there's still plenty of moisture to aid decomposition.
• Don't raise garden beds - the soil will just dry out more quickly.