← Liquid gypsum FAQ

Why does clay soil crack in summer?

Clay minerals shrink as they dry and pull the ground apart. It is normal behaviour for clay soil, and no feed or conditioner stops it.

What is happening below the surface

Clay particles are flat plates, and several of the minerals that make up British clay hold water between those plates. As the soil dries, that water leaves and the plates pack closer, so the whole soil mass loses volume. The ground has nowhere to go but inwards, and it splits. The British Geological Survey puts the zone where soil moisture swings enough to matter at roughly the upper 1.5 to 2 metres, occasionally deeper where tree roots are drawing water out.

How badly a soil cracks depends on which clay minerals it holds. Smectites, montmorillonite among them, take up the most water between their layers and move the most. Kaolinite-rich soils barely shift. That is geology rather than gardening, and it is why one garden opens up every August while the garden two streets away does not.

Is the cracking itself a problem

For plants, mostly it is a water problem rather than a structural one. Open cracks let rain run straight past the root zone and down into the subsoil, so a light summer shower does less for a border on cracking clay than the rain gauge suggests. Cracks also expose root hairs to dry air. Shallow-rooted plants and anything planted that season feel it first.

Cracking near a house wall is a different question and not a gardening one. Shrink and swell subsidence is a recognised structural hazard in the UK, and if cracks are opening against a wall or a path, that is a conversation with a surveyor rather than something to feed.

What actually reduces it

Organic matter is the honest answer. Compost and mulch hold moisture in the top layer and slow the drying front, so the soil swings less between wet and dry. A mulch two or three inches deep over moist soil in late spring does more for summer cracking than anything you can pour on. Keeping the ground planted helps too, because bare clay dries hardest.

Do not fill the cracks with sand or grit. It does not bind the soil, and when the clay swells back in autumn the material is simply squeezed into the profile where it does nothing useful.

Where liquid gypsum fits, and where it does not

Gypsum does not stop shrink and swell. That is mineralogy, and calcium sulphate has no effect on how much water a clay layer holds between its plates. What gypsum can do is help clay that disperses hold together into crumbs, which is a separate fault that often sits alongside cracking. If your soil also caps and seals after rain, the two problems are worth telling apart before you spend anything.

Does liquid gypsum work on clay soil covers the distinction in full. If you already know your clay disperses, Dr Forest Liquid Gypsum is micronised natural calcium sulphate suspended in fulvic acid, and sits alongside the rest of the liquid range.