Laterite

[Rogan]

Recently, while exploring a well-developed laterite horizon near where I live, I noticed several small bulbs growing firmly rooted in the laterite and looking very healthy indeed. For those who don't know, laterite is a very porous residual rock type that is derived from the decay and subsequent leaching of bedrock. Once all the silica and clay minerals have been leached from the rock a porous, honeycomb-like structure cemented by various iron hydroxides and aluminium oxides is all that is left.

Now for my questions (if I may?):

Has laterite ever been used as a substitute for tufa in alpine cultivation ?

Do you necessarily need an alkaline (lime rich) medium for successful alpine cultivation or would an acid medium such as laterite be OK as well - I suppose this depends on the plants being cultivated?

I have included a photo of a chunk of laterite with rooted bulbs so you can see where I'm headed with this.

[Lesley Cox]

You're right Rogan, it depends on the plants being cultivated. I would imagine there could be many acid-loving plants which would find a good home in this stuff or at least, plants which don't need lime (which is most things). If it could be drilled or chiselled like tufa, you could try many small primulas, ramondas, tiny rhodos, etc etc. While some plants can't tolerate lime, almost all which enjoy it can still live without it.

[Rodger Whitlock]

One possible drawback: laterite is notorious for very poor nutrient retention. The Coast Range of Oregon (between the Willamette Valley and the Pacific Ocean) is largely ancient lateritic soils; as a result, the area is good for nothing much but growing trees. "The Roadside Geology of Oregon" has a reasonably detailed discourse on the subject.

This is the problem that afflicts both Africa and the Amazon basin: the actual soil is extremely poor, and nutrients are only retained by virtue of intense biological activity. Cut down the jungles, plant some commercial crop, and very shortly you have a soil with no fertility whatsoever; a soil that, even worse, won't retain fertilizers.