Soil improvement is a permanent part of good gardening.
The finest border I have ever seen was at the RHS Harlow Carr Garden in Harrogate, North Yorkshire. Enormous perennials flowered profusely, some towering above my head. Not one plant was supported; no stakes, canes nor string. In most gardens they’d have collapsed, but here they stood proud.
I asked the then curator, Matthew Wilson, what magical plant food they used. ‘None,’ he replied. ‘We just maintain good soil with home-made compost, spread each year.’ Soil teems with life, from microbes and fungi to larger invertebrates, particularly earthworms. These play a crucial part in freeing the nutrients locked up in organic matter. Fungi also help plant roots to absorb nutrients.
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The right balance
Soil types vary. But to support healthy plants, they all must contain minerals, organic matter, air, water and living organisms. For good structure, soil must have the right balance of solids, air and water. Each particle will be coated with a film of moisture but there must be space for air to permeate.
If any of these constituents is lacking, soil health will decline. In nature, most soils are self-sustaining. But with extra care, gardeners can improve the structure and condition even of poor soils, for better results. The easiest way is to bump up levels of humus (non-living, fine organic matter).
For that, you need plenty of compost and a population of worms. Compost brings the humus, and worms work it deep into the soil. That was how Matthew Wilson achieved those sumptuous borders at Harlow Carr. It is also how you can turn heavy clay soil into a workable growing medium or, conversely, turn sand into moisture-retentive earth.
You can buy compost but it’s better to make your own by recycling garden waste. On a small scale, you can do it with a compost bin. These come in all shapes and sizes from your local gardening and plants retailer.
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Natural soils vary hugely. Some are gorgeous to work with, others hellish. Heavy clay soils are the slowest to improve, but every barrowload of spread compost helps. Never walk on clay soils before they have dried, even if that means planting later. Don’t dig too deeply, either. Allow the compost to boost organic levels from the top down.
The lightest, sandiest soils also benefit from organic matter, for the opposite reason. In clay, humus improves drainage, resulting in a better structure. In sand, it improves moisture retention, nutrient storage and helps plants to survive drought. You can walk on sandy soils, even before they have fully dried after rain. To beat summer droughts, you will need to cultivate and sow early each year.