Clay Soil

Improving clay soil

Clay is the most fertile soil most of us will ever garden on and the most exasperating. It holds nutrients and water well, which is the good news; it also holds them so tightly that roots drown in winter and bake in summer, and it sets like concrete the moment it dries. The fix is structure, not fertility: getting the fine clay particles to clump into crumbs so that air and water can move between them. This collection is the set of inputs that do that, from the quick-acting gypsum to the slow builders that pay back over years. Why is my garden soil sticky and heavy, why clay soil cracks in summer and why soil turns to concrete when it dries explain what you are looking at.

Gypsum: the clay breaker that does not change pH

Gypsum is calcium sulphate. The calcium displaces sodium and helps the clay platelets flocculate into crumbs, and because it is a neutral salt it does this without raising soil pH the way lime does, which matters if you also grow anything that likes acid ground. Liquid Gypsum is micronised calcium sulphate in suspension: watered in, it reaches the root zone quickly and is the choice for lawns and established beds you cannot dig. Granulated Gypsum is the slower granular form for working into new beds and vegetable plots. Does liquid gypsum work on clay soil is the honest answer, liquid versus granular gypsum the comparison, and what clay breaker is made of looks at what is in the products sold under that name.

When water runs off instead of soaking in

Dry clay repels water. Rain and hose alike bead on the surface and run to the lowest corner, and the soil beneath stays dry however much you put on. Natural Wetting Agent is a surfactant made with soap nuts and aloe vera that lowers the surface tension of water so it enters the soil. It adds no nutrients and changes no structure; it simply gets the water in, which on hard-set clay is the first job. What is a wetting agent explains the mechanism.

The slow builders

• Volcanic Rock Dust, micronised and Granulated Rock Dust. Basalt weathers slowly, releasing minerals and feeding the biology that binds clay into crumbs. The volcanic rock dust guide sets out what the evidence does and does not support.
• Humic Acid Flakes. Soluble humic substances that help aggregate clay and hold nutrients in a form roots can reach; humic acid benefits for plants covers the research.

Common questions

Gypsum or lime for clay?

Gypsum if your pH is already where you want it. Lime only if a test shows the soil is genuinely acid, because lime raises pH as well as adding calcium. Most British clays are neutral to slightly alkaline, which is why gypsum is usually the right answer.

How long does it take?

Liquid gypsum starts working within weeks; a measurable change in structure takes a season, and the rock dust and humic acid are multi-year inputs. Organic matter, mulched on every year, is what makes it permanent. How long liquid gypsum takes to work has the detail.

Can I use these on a lawn?

Yes; the liquid gypsum and the wetting agent are the two most useful things you can put on a compacted, puddling lawn. See lawn care and is liquid gypsum good for lawns.

The rest of the amendments, including the calcium and magnesium sources, are in soil conditioners; the whole liquid gypsum question set is in the liquid gypsum FAQ.