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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.
The road base and sand after the removal of the bitumen
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.
Water droplets on hydrophobic sandy soil
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.
Soil Additives
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.
20kg tub of Sand Remedy & 15kg bag Soil Solver
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 (left) and Soil Solver (right)
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.
Hi Amanda, my passion is for soil and I have been really happy with the way Soil Solver transformed my sandy garden. Moving here from Devon in UK where it is naturally a fertile loam soil, gave me heartaches with our sandy conditions in Perth for decades. Such a great result from the product, and it was a natural progression to become involved in the business when the opportunity came up.
Anyway, I just wanted to reassure you that Soil Solver is not detrimental to any native plants, even Protocea. In fact native plants establish more easily, grow larger and live longer in soil improved with Soil Solver. It has been used in many, many native gardens with great success. The trace elements and cations are in a balanced supply in the form of rock minerals and are not rock phosphates!
The amount of any type of clay needed to improve the ability of sand to hold water and nutrients, or to overcome water repellency, is the same whatever type of clay it is. Smaller amounts are used to overcome water repellency, and larger amounts are needed to increase the water and nutrient holding ability of sandy ground.
The scientists at UWA in current turf trials sponsored by the Water Corporation have recently confirmed that 5% clay (7.5kgs per sqm in the top 10cm) is needed to make a significant increase to plant available water in sandy ground. Clay holds very little water that is available to plants, and silt holds more.
Hope that this helps your understanding of adding clay and silt as a soil improvement method, it is a great boon to gardeners and well worth doing.
Good luck with your garden, you certainly have a challenging start to your ground!
Joy thank you. Where do we get silt from ?
I mix common bentonite clay cat liťter into a slurry and pour it on the garden. Works a treat on the extremely poor silica sand based, water phobic soil of the Rainbow Beach area.
I’ve also been using bentonite kitty litter on my terrible hydrophobic clayey sand here in Sydney and I think it’s helping too.
ive heard alot about this method, but am very skeptical about its application. is there any links on the web with the before and after using kitty litter into poor soils and showing its results?
Hi Tolga – not sure why you’re sceptical about using bentonite clay? The beneficial effects of bentonite in sandy soils is well documented eg http://www.petercoppin.com/pdfs/amending_improving_gutless_sands_soils_perth_wa.pdf
Clumping kitty litter made from bentonite is sodium bentonite rather than the preferred calcium bentonite but it’s widely available from supermarkets and a much cheaper way of buying it. If you’re concerned about adding sodium to your soil, I’d combine it with some gypsum which has calcium that will replace the sodium. But you do have to read the kitty litter packet/bag carefully as many brands are made from lots of other things – recycled paper, rice hulls etc
yeah, i just discovered this product this year and conducting some trials to grow fruit trees and veggies. about $30 for 15kg
any updates from your end?
I have used Soil Solver in my garden beds and am very pleased with the result.
Coastal location with mostly sand. Mixed Soil Solver with compost and manure and the difference is amazing.
Maybe cost prohibitive for large garden beds but definitely worth trying.
where can I buy it in south australia
Masters stores may get it in for you in SA, they have recently opened a store over there.