Ash contains a lot of what the tree had been soaking up from the ground. But some elements in fire become volatile and are lost in the smoke. Things like nitrogen and sulphur. Other things remain, particularly potassium and some of the trace elements and heavy metals. The big down side to ash is the high pH, or alkalinity. Ash can be as high as 10, whereas most plants prefer the 6.5 to 7 range. Passionfruit and Pawpaws like it up to about 8, but they're outside the norm.

That said, I get large amounts of wood debris which I burn in huge piles. The ash I use in the gardens and it does make a difference. But I mulch a lot with leaves, and they tend to be acidic. That helps counteract the alkaline effects of the ash.

Another way to "take the edge off" ash is to use it in compost making. During the composting process everything tends to even out/become fairly neutral.

With Crusher Dust (or Cracker Dust) it depends on what the composition of the original rock was. But usually there is a lot of phosphorus which many plants like, but most Australian natives hate. You'd probably need to have a proper analysis done to really find out what's in crusher dust.

I had a load of crusher dust dropped at my place. A native cycad neaby started to have trouble. Black Wattles started to grow in it and were doing well. Sometimes you don't know what sort of a reaction you're going to get. In places they use it for path ways and around buildings to supress grass. So many things seem contradictory about it, but I think it all gets back to the composition of the rocks it came from.

Thanks Tropic, you are very helpful my friend. I will note this in my little gardening book.

Regards
Nod

More than I will ever need now so will dig it into the gardens. Can I have some comments on what it does for garden soil please.

Increases the alkalinity ... that can be good or bad, depending on whether your soil pH is already alkaline or acidic. You may improve it for garden plants, or you may make it worse.

In other words, until you have a professional soil test done for pH, or know the basic pH characteristics of your area's soil, it's a gamble.

You can easily get pH test kits. But beware, some of them are totally useless, don't even work. Especially the "electronic" ones. A good electronic one is expensive. I got a cheap one from Bunnings. The reading was always 6.5. So I checked it in wood ash and still got 6.5. You can get the type that show different levels by colour change. They're pretty reliable.

Will look into that people, I was thinking there might be a kit out there somewhere.

Thanks again.

Nod

A little I've occasionally spread over the top of the soil and left for a month or two I've found beneficial. Mostly though - such as ash from my wood-fired bar-b-que - I simply spread over my compost bin: a three stage process; fresh stuff left for 3 to 4 months in bin one, then turned into the bin 2 and finally into a third. Turned, watered, dolomite lime added; kitchen waste, lawn clipping, prunings, some blood and bone; it all comes out nice a crumbly which I spread over garden beds other than those with natives in. Veggies and exotics thrive on it.