← Liquid gypsum FAQ

Why is my soil like concrete when it dries out?

Because the crumb structure has broken down and the fine particles have settled into a dense layer. On clay that disperses, rain does the breaking and drying does the setting.

Hard is not the same as capped

Two different faults produce a surface you cannot get a fork into. The first is compaction: the soil has been squashed, usually by feet, wheels or building work, and the air spaces have been pressed out through the profile. The second is capping, where only the top few millimetres have sealed while the soil beneath is reasonable. Dig down with a trowel. If the hard layer is a crust you can break through into decent soil, it is a cap. If it stays dense at a spade's depth, it is compaction, and no liquid fixes that.

How a cap forms

Soil holds together as crumbs because something binds the fine particles: calcium bridging between clay plates, fungal threads, roots and the gums that soil organisms produce. On clay that disperses, that binding is weak. Rain, which is close to distilled water, dilutes the salt concentration in the surface film below the point at which the clay holds together, and the plates come apart. Quirk and Schofield described this threshold in 1955 and it is still the standard account.

Once the particles are loose they wash a few millimetres down and block the pores beneath. The surface then dries into a dense, structureless skin. That is why the same soil can be a puddle one week and set like pavement the next.

What to do about it

Stop the impact and rebuild the binding. Mulch takes the force out of raindrops, which is most of the battle, and keeping the ground covered with plants does the same job. Compost and well-rotted organic matter feed the organisms that produce the binding gums, and that effect is durable in a way a mineral dose is not.

Two things to avoid. Do not dig or walk on clay while it is wet, which smears the structure you are trying to build. And do not add sand to clay in small amounts, which fills the gaps between clay particles rather than opening them.

Where liquid gypsum fits

Gypsum works on exactly the mechanism above, but only where the clay actually disperses. Dissolved calcium raises the salt concentration in the surface water and holds it above the threshold, so the clay stays flocculated instead of coming apart. On clay that does not disperse, the structural benefit is weak, and Washington State University Extension is blunt about that.

If the test comes back milky, Dr Forest Liquid Gypsum goes on with a watering can and needs no digging in. If it comes back clear, spend the money on compost instead. How liquid gypsum works has the mechanism in full, and the rest of the liquid range covers the feeding side.