How to use Gypsum on Clay Soil

Gypsum is a mineral that helps to improve the physical structure of the soil and reduce the pH.

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For those gardeners who are used to working with clay soils, there’s no need to tell you about the virtues of gypsum.

However, if you’re new to gardening with clay soil, you might be wondering what gypsum is and why it’s such a good addition to your heavy clay soil.

What is gypsum?

Gypsum is a soft mineral often found in shallow lake beds, especially salt lakes.

In scientific language, it’s known as hydrous calcium sulphate or CaSO4.2H2O.

In Victoria, for example, gypsum deposits are mainly found in the Mallee and Wimmera districts and in northwestern Victoria. 

How does gypsum work?

When applied to alkaline soils, as many clay soils are, gypsum helps to improve the physical structure of the soil and helps to reduce the pH.

In other words, the addition of gypsum helps to break up the soil into smaller, crumblier pieces.

This not only makes the soil easier to work with but also helps to improve the drainage of heavy clay soils.

This is particularly important because heavy clay soils can become quite waterlogged and the clay can often bind the nutrients in the soil, making them unavailable to plants.

As an added bonus, gypsum also adds nutrients such as calcium and sulphur to the soil.

How to use gypsum clay breaker

Richgro gypsum clay breaker is available at Bunnings.

There are various ways that you can use gypsum clay breaker to help improve your soil.

For new garden beds

  1. Spread 1 kg of powdered gypsum for every square metre of soil.
  2. Dig the gypsum into the soil at around 10 to 15 cm deep.
  3. Water well.

It’s important to note that it might take at least a couple of months for the gypsum to make any difference to the structure of the soil.

To get a quicker result

When planting new trees and shrubs, you can add a handful of powdered gypsum to the bottom of the planting hole and then, add some liquid clay breaker which will work a little faster.

Once you’ve planted the tree or shrub, water well with a filled watering can that you’ve added a little more liquid clay breaker too.

How to use gypsum on your lawn

For lawns grown on clay soils, compaction can be a fairly common problem.

You can use gypsum on your lawn to alleviate the compaction and help your lawn to grow better.

Here’s what to do:

  1. First, you want to aerate your lawn. You can do this with a garden fork or lawn aerator by poking holes all over the lawn area. Alternatively, you can hire a rolling aerator if you have a larger lawn area to cover.
  2. Spread 1 to 2 kg of gypsum for every square metre of lawn area.
  3. Rake in the gypsum as best as you can and water well.

The best time to do this is in autumn or winter as it will give the gypsum enough time to work on the structure of the soil before the grass springs back into strong growth again.

How long does gypsum take to work?

In general, you’ll find that it will take around 2 to 3 months for the gypsum to have a positive impact on the structure of your soil. 

On the other hand, liquid gypsum is much faster acting. In fact, it will start to work on the soil structure immediately but will take around 6 to 8 weeks to make significant improvements.

How to determine if your soil needs gypsum

If you have heavy clay soil, you know that it will benefit from an addition of gypsum.

But what about if you’re not sure whether your soil is clay or not?

Here’s a little test that you can do:

  • Grab a jar with some clean water in it.
  • Put some of your soil into the jar and shake it until the water goes milky.
  • Let the jar rest for about 5 to 10 minutes. If the water is still milky and not clear, then your soil will benefit from an addition of gypsum.

Where to buy gypsum for soil?

You can find bags of gypsum for sale at your local garden centre or Bunnings.

In fact, any hardware or produce store should have bags of gypsum that you can buy to add to your soil.

FAQ

How much of the gypsum should you add to your clay soil?

As a general guide, you should add gypsum at a rate of 1 kg for every square metre of soil.

Is liquid gypsum better?

Liquid gypsum has the same properties as the powdered form except it will start working faster to help break up clay soil. In fact, it starts working immediately after applying.

Is it possible to apply too much gypsum to the soil?

Gypsum should be applied in the recommended quantities on the pack. If you add too much gypsum it can result in the elimination of essential minerals such as iron, magnesium, and manganese.

Photo of author

Annette Hird

Annette Hird has an Associate Diploma of Applied Science in Horticulture. She has worked in a variety of production nurseries, primarily as a propagator. She also had the responsibility of a large homestead garden that included lawn care, fruit trees, roses and many other ornamental plants. More recently, Annette has concentrated on improving the garden landscape of the homes that she has lived in and focused a lot of energy on growing edible plants as well. She now enjoys sharing her experience and knowledge with others by writing articles about all facets of gardening and growing plants.