Brisbane has many soil types ranging from poor nutrient carrying Sand, deep red loamy soil, dark alluvial soil and clay.
The most widespread is shallow, gravelly red and yellow loam over a deeper layer of heavy clay. In many parts of Brisbane, soils are often low in nutrients, compacted and poorly drained due to large-scale urban development which has changed the landscape dramatically.
Many of our houses and gardens started their life as farming land of a heavy clay soil and to transform these areas from bare and compact clay to beautiful landscaped gardens, extra time will need to be spent preparing the earth and required knowledge of the products to use.
The main characteristic of a heavy clay soil is the small particles from which it is made up from with very little pore space, in essence, clay soil has very fine particles, tightly compacted. The problem generally isn’t one of nutrient deficiency but rather structure. Clay soils tend to have a high water holding capacity, drain very slowly and lack required aeration. All these characteristic create a very poor growing medium and a difficult environment for plant roots. The solution is to basically add various elements to your soil to create an open, more air-filled and more freely draining structure to promote better root growth.
Four handy tips dealing with Clay Soil
1. Add Organic Compost
2. Use Gypsum
3. Build Up
4. Use Mulch
Add organic matter, such as compost and manure, to the clay soil by forking it through the top 20 cm. Products such as Earthgrow Soil Conditioner and Clay Breaker, Enviroganics Premium Compost and Mushroom Compost are perfect. But remember, these composts can alter pH levels, so the key is to plan ahead and know what you intend to plant. Adding compost improves soil structure by binding the clay particles into larger crumbs. Another additive is Coarse River Sand, though there is no nutritional benefits.
Gypsum is a form of calcium sulphate, which also helps to break up clay soil and bing particles into larger crumbs. Mix it through the soil while incorporating the organic matter mentioned above then water in well. You can use between 0.5-1kg of gypsum per square metre of garden bed.
Build Your Garden Up:
Don’t dig down, build up! When planning a new garden bed, consider raising your beds and focus your energy on the topsoil through the methods above. Don’t dig holes for new plant down into heavy clay, instead improve the topsoil so the plants can establish in a friendly environment. As the plant grows, matures and strengthens the root system will explore into the heavier clay.
This is often the best method when establishing a vegetable and herb garden as it allows much easier access to your crop, plus far more control over the soil quality.
Mulch Your Beds:
Because of the tiny particles, clay soils have a tendency to cake up and dry out in the hot sun. This means the soil will become extremely hard and hydrophobic (water repellent). To avoid this problem, always spread a good layer of organic mulch over the soil after planting, and regularly throughout the lifetime of the garden. It is always best practice to schedule a spring working bee and top up your soil, mulch and fertilise to prepare your garden for the hot summer!
A Clay Soil Planting Scheme
1. Scaevola ‘Purple Fusion’ is a perfect ground cover as it grows very flat and low and needs very little trimming. It has excellent drought and cold tolerance. It grows in full sun or very light shade and flowers from September through to December.
2. Lomandra ‘Shara’ is a tough and hardy grass like plant. This tufting Lomandra grows to 40cm high and 50cm wide and can tolerate drought, frost and wet feet. It suits full sun through to moderate shady conditions.
3. Lilly Pilly ‘Sublime’ like many of its brothers and sisters, is great for screening and hedging. With a lovely dense form can grow to 5m tall and around 2-3m wide. It can tolerate both drought and cold, but prefers a sunny spot with only moderate shade.
Clay and Lawns
If you are fortunate enough to be planning a new lawn over a clay base many of the same rules apply as for a garden bed. Your options include attempting to improve to soil structure through the addition of coarse sand, organic compost and gypsum. Depending on the size of the area, achieving this by hand might be a bit too much hard graft. If you can get a machine such as a bobcat or dingo involved your job will be far easier. The second option is to build your soil up with imported topsoil such as Mineral Commercial Underturf Blend or Ultagrow Hydrocell Soil. You will need at least 100mm of loose and free draining soil to achieve good results.
If your lawn is already established, once again gypsum and coring or aeration may be your best form of attack. Using a corer you remove small plugs of the existing clay soil, which can then be top-dressed with a sand/gypsum blend. Remember, you won’t achieve instant results using this method, but over the course of a few treatments your soil structure will improve dramatically.