Clay Soil - Gardening Australia (2024)

FAQs

How to improve clay soil in Australia? ›

The lack of large pore spaces in clay soil restricts water and air movement, resulting in easily waterlogged and anaerobic soils. The only practical way to improve this is the routine addition of plenty of organic matter (can be compost or manure) and fostering the activity of earthworms and soil micro-organisms.

Clay is a great soil to have in your native garden – it's full of nutrients and retains water. BUT, not all natives like it! In fact, most plant labels say, 'well drained soils', which can put us off. However, I've been growing native plants in clay for over 20 years and have had many successes.

Amending your soil properly can overcome heavy, compacted clay and get it back on track for healthy lawn and garden growth. Adding materials such as organic compost, pine bark, composted leaves and gypsum to heavy clay can improve its structure and help eliminate drainage and compaction problems.

Generally, soils that contain greater than 30% clay are considered unacceptable as topsoil material because soils with high clay content slow water infiltration and air penetration. Clay soils can be difficult for roots to penetrate, and can be very hard for gardeners to cultivate.

Clay soil loves added humus, that decaying plant and vegetable matter that good compost becomes. Although composting can be a high art form, if you simply add decomposing plant matter like leaf mold, coffee grounds or kitchen peelings you continually improve your clay soil and improve its fertility as well!

The first step is to add gypsum to the soil. Apply gypsum at 1 kilo per square metre, digging this into the top 10-15cm well. Gypsum works on the clay, breaking it up into small crumbly pieces making it easier to work with and also improves drainage.

Organic matter is one of the key ingredients in amending a clay soil. Organic matter helps with drainage as well as adding nutrients and improving the soil's texture. A great source of organic matter is composted chicken manure pellets (Super Booster, Blood & Bone Plus or Super Growth).

Avoid using sand or peat moss as an amendment to compacted clay soils as they will make the problem worse. Rather, consider adding high-quality organic compost, pine bark, composted leaves, and/or gypsum. These products will help improve the structure of the soil and eliminate compaction issues.

Lime is used to fix clay soil. If you have acidic soil such as Georgia Red Clay the lime can help reduce it. This will eventually be lost in areas with high rainfall. But most clay is alkaline and adding lime will make things worse.

Bark, manure, leaf mold and compost are among the organic amendments commonly used to improve clay soil, Brewer noted. Applied to the soil surface, these materials form a protective blanket that slows evaporation and reduces soil hardening.

What vegetables grow best in clay soil? ›

Best Vegetables for Clay Soil

Lettuce, chard, snap beans and other crops with shallow roots benefit from clay soil's ability to retain moisture, and broccoli, Brussels sprouts and cabbage often grow better in clay soil than looser loams because their roots enjoy firm anchorage.

Soil that is too heavy on clay may require the addition of sand, but in general, the key to fixing imbalance soil is to blend it with organic matter. Mixing organic material into the soil attracts beneficial organisms that create a higher quality, loamy soil over time.

To create a real change in a clayey soil structure, you would need to add a 1:1 ratio of sand to clay. Considering the actual volume of clay soil underfoot, that equates to a lot of sand. It is far more practical to use organic matter to help break up clay soil.

Adding lots of organic matter such as compost, farm manure, or shredded leaves to clayey soil will allow it to drain more easily and hold the right amounts of water and air for better plant growth and increased biological activity. Adding sand can be tricky and typically is not recommended to be added to clay soil.

Quick take: Clay soils drain slowly, and sandy soils drain quickly. For this reason, the thinking often goes that adding or tilling sand into a clay soil will improve the drainage characteristics. Unfortunately, this generally won't work and there are better ways to improve the drainage and quality of the soil.