Sahara desert storms alter native US soils permanently. Mt St Helens altered native US soils permanently. Any windblown or water carried deposition alters the soils. And if those deposits are inorganic and become locked into the soil matrix by plants, they can alter them permanently. That's how most (all?) soils are built. But that alteration isn't (necessarily) to the existing soil, it's through the creation of a new higher layer of soil.
So yes, you can certainly topdress with red volcanic sand. What won't happen, however, is it won't incorporate itself into the existing soil and lighten it.
Because we are on limestone, the soil here is...well there really isn't any. We have a limestone base covered with limestone rubble interspersed with organics. With out root cover and constant deposition of organics both of those quickly erode/decompose/dissolve and disappear leaving a bare limestone surface. So there's really no such thing as inorganic soil here other than what's been placed here by windstorms and volcanoes and the final biodegradation products of the bits of silica and other minerals the plants manage to extract from the rock layer over time. Once we started topdressing with granite sand every few years, the plants all did much better because we introduced an enduring layer. We alternate that with annual leaf fall and organic mulching. The net effect though isn't to alter what's below, it's to raise up the soil column and the garden. Given the chance, the plants are doing this anyway, we're just speeding up the process. The physical height doesn't raise that much because the organic materials below are continuing to break down. A continuous cycle of that does eventually add a permanent soil to the landscape.
California is different. I suspect your soils are all inorganic depositions to begin with. So over time they won't be shrinking down like ours as all the organics are consumed. You'd simply be piling a new layer of different composition on top and that may not be as beneficial as it is for us. However, if you piled a thick enough layer on top you'd be giving the plants an entirely different substrate in which to grow. In the few cases where we've rototilled over the years, as we're stripping a bed out and recreating it, tilling in organics hasn't resulted in a permanent benefit. But tilling in granite sands most definitely has as it carries those further down into the soil column, and they stay.
John
Austin Tx
On Friday, February 5, 2021, 10:56:21 PM CST, Robert Lauf via pbs <pbs@lists.pacificbulbsociety.net> wrote:
Current practice by whom?
On Friday, February 5, 2021, 11:52:35 PM EST, Nan Sterman via pbs <pbs@lists.pacificbulbsociety.net> wrote:
I can’t comment on the red volcanic sand in particular but don’t incorporate it into your garden soil. You can’t alter native soils permanently, and current practice is to plant into native soils only, without any amendments, regardless of what you are planting.
Nan in So Cal
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