What is liquid gypsum?

Quick answer. What is liquid gypsum? Ordinary gypsum, calcium sulphate, milled finer than flour and suspended in water so you can put it on with a watering can or sprayer. It isn't truly a liquid. Water holds only about 2.5 g of gypsum per litre, so most of it stays as fine particles and you shake the bottle first. It adds calcium and sulphur without changing soil pH.

By Joe Barrington, founder of Dr Forest · Published August 2026 · Updated 6 November 2026

Why I sell liquid gypsum

It arrives ready-made and I pack it here in Stockport. I added it to the range because it is for everyone who grows. In the UK most of it goes to people with clay, poor drainage or waterlogging, and that is a fair reason to buy it. It is also a really good soil conditioner, and I would recommend every grower uses it at least twice a year. For edible crops, apply it before you plant and again before the flowers start. It pays where calcium or sulphur is what is holding your plants back, and the calcium strengthens the plant's cell walls.

Is liquid gypsum a solution or a suspension?

A suspension, and that is the heart of what liquid gypsum is. Water holds about 2.5 g of gypsum per litre at room temperature, and no amount of stirring gets more into solution [2] [3].

The Liquid Gypsum I sell has roughly 830 g of gypsum in every litre of concentrate. Mixed at the lawn rate of 10 ml in a litre of water, that puts about 8 g of gypsum into each litre in the can, more than three times what the water can hold. So even after you dilute it, most of what lands on the soil is fine solid particles. To carry a dose at the clay rate fully in solution, a 20 m² lawn would need about 100 litres of water instead of 20.

Solid particles settle. In still water a 5-micron gypsum particle sinks about 6 cm an hour, so the bottle forms a white layer at the bottom between uses, and a can stays mixed for as long as it takes you to water. Shake the bottle hard before you measure, and give the can a swirl if you stop halfway.

What does micronising do?

The one I sell is milled to an average of 5 microns. Weight for weight, that gives the gypsum about 400 times the surface of a 2 mm granule, and finer gypsum releases its calcium and sulphate faster in lab tests [4]. The 2.5 g ceiling stays where it is: above about a micron, particle size only changes how fast gypsum gets there [2].

Size also decides whether you can spray it: five-micron particles pass a 200-micron sprayer filter and stay in suspension while you water. A kitchen grinder leaves grains in the hundreds of microns, and even a 100-micron grain sinks 7 mm a second, so it is on the bottom of the can within a minute or stuck in the filter.

What is liquid gypsum, chemically?

Gypsum is calcium sulphate with two molecules of water locked into each crystal: CaSO₄·2H₂O. Pure gypsum works out at 23.3% calcium and 18.6% sulphur by weight, in line with agronomy guidance [5]. Anything sold as gypsum claiming a lot more calcium has been heated to drive the water off, or isn't gypsum.

Labels can confuse. UK and EU fertiliser rules declare calcium as CaO and sulphur as SO₃, so the same pure gypsum reads 32.6% CaO and 46.5% SO₃. Nothing has been added: it is a different way of counting the same calcium and sulphur.

Liquid Gypsum is gypsum milled fine and suspended in water. It carries 19.55% calcium and 15.31% sulphur, weight in volume, which reads as 27.35% CaO and 38.23% SO₃. That is 195 g of calcium in each litre, and the gypsum is suspended with fulvic acid.

How does liquid gypsum work once it reaches the soil?

Watered on, the particles wash into the top of the soil and release calcium and sulphate into the soil water a little at a time, topping it up as roots take them out, so each dose works as a small reserve. Gypsum is a neutral salt, so it adds calcium without raising pH; to change soil pH you need lime or sulphur instead.

Clay and organic matter hold on to calcium, so most of it stays near the surface: in a 26-year Australian trial on sodic soil under sugarcane, most of the calcium from gypsum stayed in the top 25 cm, though some reached 1.25 m [6].

As a general root drench, shake the bottle, mix 5 ml fresh into a litre of water and water it over one square metre, before planting and again before flowering or fruiting, never onto frozen ground or into standing water. The dose before flowering matters most for tomatoes, because blossom end rot in tomatoes comes down to calcium reaching the fruit, and steady watering counts as much as the calcium. Whether it will change the structure of your clay depends on the clay. My guide to whether liquid gypsum works on your clay shows you how to check, and gives the full clay and lawn programmes.

Questions people ask

What is liquid gypsum?

Liquid gypsum is ordinary gypsum, calcium sulphate dihydrate (CaSO₄·2H₂O), milled to particles a few microns across and suspended in water. It is a suspension because water holds only about 2.5 grams of gypsum per litre.

Is liquid gypsum water soluble?

Only slightly: water holds about 2.5 grams of gypsum per litre at 25°C. Most of the gypsum in liquid gypsum stays as fine solid particles, which is why you shake it.

What is micronised gypsum?

Micronised gypsum is gypsum milled to particles measured in microns, thousandths of a millimetre. Finer particles release calcium and sulphate faster, though milling doesn't change how much gypsum water can hold.

Is liquid gypsum a fertiliser?

Yes, it supplies calcium and sulphur in forms roots can take up. It has no nitrogen, phosphorus or potassium, so use it alongside a general feed rather than instead of one.

Is liquid gypsum allowed in organic growing?

Organic growing rules allow gypsum where it is of natural origin. It contains no carbon, so it isn't organic in the chemist's sense, and natural vs synthetic gypsum covers how to tell which kind you have.

Joe Barrington

Founder of Dr Forest, Stockport. Joe formulates and blends his own Dr Forest feeds. Liquid Gypsum arrives ready-made, and he packs it in Stockport.

Sources

1. Rakkar, M. and LaBarge, G. (2024). Response of soils and crops to gypsum application in Ohio. Ohio State University Extension fact sheet ANR-0153. ohioline.osu.edu
2. Lebedev, A.L. and Kosorukov, V.L. (2017). Gypsum solubility in water at 25°C. Geochemistry International 55(2): 205 to 210. doi:10.1134/S0016702917010062
3. Abrol, I.P., Yadav, J.S.P. and Massoud, F.I. (1988). Salt-affected soils and their management. FAO Soils Bulletin 39, section 4.4.1, Amendments. fao.org
4. Tang, J., Bullard, J.W., Perry, L.N., Feng, P. and Liu, J. (2018). An empirical rate law for gypsum powder dissolution. Chemical Geology 498: 96 to 105. doi:10.1016/j.chemgeo.2018.09.013
5. Incitec Pivot Fertilisers. Gypsum. Agritopic fact sheet. incitecpivotfertilisers.com.au
6. Green, H., Larsen, P., Koci, J., Edwards, W. and Nelson, P.N. (2023). Long-term effects of gypsum on the chemistry of sodic soils. Soil and Tillage Research 233: 105780. doi:10.1016/j.still.2023.105780