(…or, why I mulch and compost….)
Robbie over at Palm Rae Urban Potager made a great post about the importance of soils. With the 21st being ‘Save the Soils’ day, I thought I’d share a bit of info about what is under my feet.
To say that my soils are sandy and rocky is an understatement.
What passes for topsoil in much of Australia is in fact nothing more than ancient decomposed rock particles. This describes my yard: the soil is a mix of decomposed Sydney sandstone, Ironstone and a little bit of Granite.
The most surprising feature is that there is almost no organic matter: this is partly because the whole garden is on a steep slope and organic matter washes away in rain, but even in the lower parts of the garden, there is almost nothing. Despite this, the garden manages to house over a dozen very large, healthy trees (native and exotic).
But, as you can see from my humble attempts in this blog, even these impoverished soils support plant life. If it weren’t for the high rainfall in this area and the rock minerals present as a result of the decomposition of ancient stones, creating a garden in just sand and rubble would be seriously challenging.
Challenging alright…who has light beige coloured top soil?
Then there are the rocks…..any time I create garden beds, I dig, mattock and lever out vast amounts of them. These are just some of the piles in out-of-the-way parts of the garden:
But these rock piles are slowly being re-used to create edging, raised beds and dry-stone retaining walls….
……and the little bits of rubble will be spread under pathways with a decorative gravel layer on top and it will be used to make Swales once I have finished terracing the site.
A great thing about these dry-stone walls is that they make fantastic insect-hotels – in fact they are the original insect hotels, long before the term was even invented! Pick up any of the stones and there all sorts of insects (both good and bad); lizards, spiders, centipedes, ants, woodlouse, etc using these as shelter and as their own supermarket…although in this supermarket, all the insects feast on each other.
Naturally I make my own compost, but obviously it’s no where near enough for a 1000m² (¼ acre) of garden.
There are of course positives to having this soil type: in addition to being very free-draining, sandy soils are easy to dig, don’t waterlog and because of all the rock nutrients, have fertility despite no organic content.
But it needs more organic matter, lots more.
Now as I can’t make enough compost (yet – each batch takes a few months) for the rate of new garden beds I am making, I have to bring in the next best thing – mulch.
I would mulch anyway to both conserve soil moisture as well as stopping run-off during heavy rain and protecting the soil from freezing in winter.
I use Sugar Cane mulch which is a by-product of sugar processing (once upon a time it was just burnt). Sugar cane mulch contains Nitrogen, Phosphorus, Potassium, Calcium, Magnesium and Sulphur so actually adds nourishment as well as enriching the soil structure. The mulch breaks down quickly and doesn’t deplete Nitrogen from the soil like bark mulches can. Nor does it change the pH like pine-bark or pine needles. Here is an example of the soil after only 6 months of mulching with Sugar Cane:
Compare that with very first photo! Much more brown, much less beige – heck, there’s even a hint of black, just like soil should be!
I just need to add another 20cm/8″ of this sort of organic matter, as well as leaf mould (another reason why I have planted so many trees), before I have anywhere near what most people take for granted as the soil under their feet.
But at least it is much, much easier to fix a sandy soil than a clay one, so for that, I’m grateful! And there is one piece of advice that I learnt many years ago: “Feed the soil, not the plant“.
Happy Gardening and Happy Soil Day 🙂