Volcanic rock dust- any good?

[More basil]

Today I spent the morning spreading a ton of volcanic rock dust over a very large vegetable garden where I work as a trainee. The dust was bought by the garden owner who swear by it. However, the 'old hand' gardeners I work with are somewhat sceptical to its benefits.

So I am curious-what do people think? Is it any good or are my arms aching in vain? It is alleged to add more nutrients to your veg and generally improve the soil. I know volcanic soil is fertile but I don't know if dusting your veg bed could really make a difference.

[mothhawk]

There's an old thread here about it...

http://www.growfruitandveg.co.uk/gra...ust_69010.html

[Martin H]

I'm a sceptic on this.

Firstly, it seems to me that unless you are on unusually mineral-deficient soil - i.e. peat soil or very hungry sand/gravel soil - there's no logic to why it should make a significant difference. On my clay soil I think organic matter to open it up should release plenty of minerals from the clay.

Secondly, I bought a bag to mix with the multi-purpose compost and see if it made a difference to the flavour of my tomatoes. I was surprised by how coarse it was; I was expecting like talcum powder but actually it was quite gritty. It would take a few tens of thousands of years for those pieces to break down enough to release the minerals for the roots to absorb.

Finally, I didn't notice any difference in my tomatoes. Not scientific I know but I'm not persuaded enough to try a proper trial.

I'd be interested to hear other views though, see if it changes my mind at all.

[Martin H]

Ooh I see I posted in the old thread too, I'd forgotten! At least I'm not contradicting myself...

[More basil]

Thanks both- The old thread made an interesting read. And yes, it is indeed quite gritty though I shouldn't like to spread it when very dry as some of it would be dusty enough to be breathed in. It was spread on clay soil so I would imagine adding more structure to the soil would be more beneficial as there are plenty of nutrients in the soil already. (We also spread copious quantities of mushroom compost.)

[veggiechicken]

Ooh I see I posted in the old thread too, I'd forgotten! At least I'm not contradicting myself...

You posted on http://www.growfruitandveg.co.uk/gra...ust_76517.html too Martin

[KevinM67]

How much would a ton of volcanic rock dust cost ?

[More basil]

Not cheap. Think around £250...

[Snadger]

It cost me a fiver for a kilo in two boxes! I used it around my tomatoes which were ok, but I didn't do a control so they may have been ok anyway!

[More basil]

Hmm, yeah, things are on a somewhat grander scale in my 'work garden'. In my extremely modest pots only home garden I agonize over the price of a bag of compost... But it's good fun to try (largely organic) gardening on a big scale.

[FeedTheSoil]

Not needed

I fell for the sales patter a few years back but its not needed as far as I'm concerned, what soil is deficient of rock?

Soils are made up of rocks (sand, silt and clay), its just different size particles with sand being the biggest and clay the smallest. Rock contains all of the nutrients required to grow plants. The key is to get the biology functioning correctly in the "soil food web" and its via these symbiotic relationships with fungi and bacteria that makes these nutrients available to the plants. He would be better served by spending the money on organic matter as this makes bacteria thrive which brings in the worms to eat them, releasing their nutrients in the process. Even better get making his own hot compost and use it to innoculate the soil like a probiotic, it gets these natural cycling (nutrients, water etc) functioning correctly in a short time.

That all said it could be useful if your growing for a long time in pots in a peat only compost. You would need to innoculate your roots with mycorrhizal fungi to make it available to the plants though.