Further to my first blog about our backyard bitumen challenge, the following provides more detail about how I dealt with the road base and started improving our ‘gutless’ sandy soil.
Once we had removed the bitumen we had to consider whether to keep the underlying road base or remove it and have soil brought in. I have been asked what made up the road base and the answer is I’m not sure. I believe it was a heavily compacted layer of blue metal of varying sizes and rock / blue metal dust, the depth of which varied from a few centimetres to 10-15 cm. Removal seemed like a very expensive project and given that our interest for our home garden tended more towards native and waterwise plants we thought we might be able to work with what we had.
Some internet research gave us reason to hope that all was not lost. One article in particular, about a successful native garden that had been established in road base, was very encouraging. Whilst this garden was in Queensland and I think the benefit of the road base there was drainage, it was enough to convince us that it was worth sticking with our road base and giving it a shot.
I must admit though, there are times when I have regretted this decision. When I see gardening programmes where the gardener / presenter plunges their spade or fork seemingly effortlessly into the ground to dig a planting hole, I am very jealous! Our early planting sessions commenced with a pick to hack a hole through the road base to the sand below.
In order to give our plants a (hopefully) reasonable chance of survival, I use, depending on the plant, compost and/or a commercial soil improver, a clay additive and a slow release fertiliser. Perth’s soils are often referred to as ‘gutless’. This translates to a lack of water (and therefore nutrient) holding ability, very little organic matter and poor soil structure – none of which are good news for the gardener. So what to do? Adding compost is a good start but the addition of clay is also said to help immensely.
Western Australia has 2 locally produced clay based products designed to turn our gutless sands into soil. These products are Sand Remedy and Soil Solver. I first came across Sand Remedy a few years ago, and have been using it since. When I first starting planting in our backyard, the soil was highly hydrophobic. Any water would just run straight off and pool at the lowest point. It would take a long time to be absorbed into the soil. Sand Remedy definitely helped with this problem.
When planting I put a smallish amount in the planting hole and mix it with the existing soil, backfill around the plant and then sprinkle some Sand Remedy around the plant, scratch it in lightly and water. If the soil is still water repellent, I add some more Sand Remedy around the top of the plant and water again. I also water plants in using Seasol and am a big fan of this product. It has definitely brought some plants ‘back from the dead’ for me.
Sand Remedy is a bentonite clay product whereas Soil Solver is based on kaolin clay, and there appears to be a bit of a debate as to which is best for the garden. I have heard, but don’t know whether this is accurate or not, that Soil Solver might be a bit rich for some of the more sensitive natives, such as those from the Proteaceae family. The websites for these products are Sand Remedy and Soil Solver. I would be interested in any feedback you have in relation to either of these products.
A 5kg tub of Sand Remedy will set you back about $37. At the application rate stated on the tub, 5kg will cover 16sqm to a depth of 100mm. However, the website also states the following “For new garden beds in very poor, sandy soil, a much higher once-off application of up to 1kg per square metre, dug in to a depth of at least 100mm and up to 300mm will provide lasting improvement in water holding ability of the soil”. A 15kg bag of Soil Solver costs about $25 and the recommended application rate is 7.5kg per sqm.