Topic: Rock Dust

[InfraDig]

With all the rain we have been having, is it time to think about rock dust? I have not used it before. Is it worthwhile? I see B&Q sell it, just under £6 for 10KG.

Thanks for any thoughts!

[Jayb]

I can't give a recommendation, as I've not used it before. But I'm planning on adding some to my poly tunnel beds this year and to the worst flooded areas of the veggie patch, once they become workable, still a while off yet. They grounds had a tough time the last two years and I thought it might add a little something back.

[BarriedaleNick]

I think many people's soils will be low on nutrients this year after all the rain but Like Jayb I cannot comment on Rock Dust as I haven't used it.  I intend to give the site a good manuring this year plus helpings of chicken poo and the lovely waste we get from the local Brockley Brewery.

[goodlife]

I use it all the time..and even now I have several sacks to get spread around the plot.
It is one of those 'funny' things..you cannot quite put your finger on it to describe the effect..BUT, if I really have to try hard. I would say my crops have been extremely desease resistant and particularly perennial crops seem to be in constant production mode  I have mentioned this before..but some years ago I had spillage accident with rock dust sack...the bag did split under apple tree and instead of trying to salvage it all..I just spread it around the root area and left it to it. Ever since that small tree has been cropping its 'socks off' and practically spotless apples...only 'negative' side to it that I have to thin most of the apples away to allow others to grow biggies  That was the start for my rock dust 'obsession'...
I use rock dust with almost any compost mixes as replacement for grit, rockdust is essentially gritty with some dust around the stony bits....I add some in compost bin when it is been filled up...some is always added into planting holes too .
The rockdust effect is not something really obvious nor rapid...but after while you realize that you can tell difference from what the crops have looked before....everything looks very healthy and you find that there is no need to add that much fertilizers neither...it has kind of 'vitamin pill' effect rather than fertilizing/instant feeding effect...plant look kind of 'happy'
The main reason why I use it so liberally around the plot..is that I truly believe that lot of the elements in the dust will end up nourishing me when those veggies are eaten. Lot of shop veg doesn't contain the same amount of vitamins and essential minerals that were available from farmlands generations ago...all spent up. To make myself healthier, I 'feed' the soil first
I convinced our secretary that we need to buy rockdust supply for our shop...and we did, and I promised to buy it all if it doesn't sell. Well, we did sell first order almost instantly..and had to get another pallet full for this year. I was quite surprised some old timers being keen to buy it too...they don't usually go for these 'modern whims'...can't have too much of a good stuff..  

[Digeroo]

I put some on my strawberries and raspberries last year with the hope of improving the flavour.  I also have some green  manures and have put some on two patches to see if it makes any difference, and so far nothing has changed.   I certainly have more significant good effect from charcoal and wood ash (not on raspberries).   

I thought it was the nitrogen and water soluables that leached out rather than the minerals. I would not recommend letting it get wet as the bag become amazingly heavy.  It also blows in the wind so you need a damp day to spread it as you are not supposed to breathe it in.

So far not convinced either way.  It is reputed to reduce diseases.  But it is very difficult to test for not having something.  My apples trees cropped their socks off even without rock dust last year.

I have bought a second bag but not sure whether that is more hope than actual known effect. 

[goodlife]

I think the effects will take longer season or two to really kick in..after all it have to go through many 'creatures' living in soil system to before the 'stuff' become available form for plants. Now I'm claiming that how true my belief is..it is something that I seem to been reading from somewhere...
As for improving flavour for berries...hmm..that is difficult one..there is so many variables to why something might taste really good or not. I can't claim that any of my veg and fruit does taste good/better because of the rockdust, but nor have I really used it for that reason...I have always got rid of those that doesn't deliver with taste wise..that includes big bed of yellow raspberries ...what a waste of plants and effort that was, but I did learn a lesson from it.

[Ian Pearson]

Firstly, I should say I have not used it, but have been thinking about it. This Phd thesis http://theses.gla.ac.uk/617/1/2009campbelllphd.pdf (warning, 385 pages!) includes tests which shows no improvement in growth over using compost as soil amendment. At first this seems disappointing, but then compost works pretty d**n well!
I think it also depends on one's soil type; a fine clay soil already has very fine soil particles, and therefore a massive surface area for mineral transfer. In effect clay is just like rock dust, and would only benefit from rock dust addition if the soil's parent rock contained a specific deficiency. A sandy soil on the other hand would benefit far more.
I think rock dust could be prone to eroding out of soil (either by water transport, or surface wind blow erosion), so adding it to compost, as suggested by Goodlife, where it would be chelated into the humic material seems like the most effective use.

[digmore]

I had the pleasure of living in southern Tenerife for a short while, long before the island disappeared under concrete. The island was covered with tomato farms and banana plantations, the natural flora and fauna were vibrant and abundant.

The water from the volcanic mountains brought down minerals. That water was well manage throughout the plantations and along with other fertilizers it all added possibly to the abundance and quality of the crops.

The soil was a rich red colour but dried out almost to dust.

The inclusion of rock dust in any soil composition in my opinion can only be beneficial if its contents can be defined ie. mineral content.
Rock for rocks sake, doesnt benefit soil unless its clay based.

Unfortunately, two of the side effects of the rich mineral content in the water, was to corrode and fug up the plumbing and to give kidney and urinary problems to the population after drinking the water.

If rock dust is not a fad and its use lasts over, say 5yrs in a controlled situation, it will be interesting to see if its benefits are borne out in crop weights and quality.

Digmore. 

[goodlife]

This Phd thesis http://theses.gla.ac.uk/617/1/2009campbelllphd.pdf (warning, 385 pages!) includes tests which shows no improvement in growth over using compost as soil amendment. At first this seems disappointing, but then compost works pretty d**n well!

THANK YOU for that link...I've only just started to go through it... Very interesting reading indeed..my poor head, it is good 'work out' for it..

[Robert_Brenchley]

I think a lot depends on what sort of rock it is. Silica, which makes up a great many sandstones, will be inert. Limestone and clay we know about. Many volcanic rocks will produce fertile soils because they're made up of minerals which are unstable at the surface and soon break down once they've been ground up fine.

[goodlife]

It took me couple of hours to read the link 'through'.. jumpingly so...and all trials in that thesis were based short term trials.
They ended the papers saying rockdust didn't show having any/or little evidence to show positive fertilizing value but there would need to be more research done for its long term effects as well as different trial situations than those that were used now..agricultural situation and horticultural..as in pot culture.

Well...I've used it 'long term' and would not be without it...

[Digeroo]

I was reading that organic veg has more minerals in it and my logic for using it was that I cannot expect minerals out if I do not put minerals in.   If I keep taking the crops away where do the minerals come from. 

The land had been used for sheep grazing and presume that they used up minerals.   Perhaps there is a case for using bone meal or BFB.

[Ellen K]

I'm interested to read that PhD thesis too but having got to this on Page 2....

No yield effects due to rockdust addition were apparent after 3 years of the field
trial. In addition, rockdust did not impact on plant nutrient content nor did it
affect the soil chemistry despite 3 years of weathering that was considered
sufficient time to release nutrients to the soil.

.....I wont be buying any.

[goodlife]

Code: [Select]

I'm interested to read that PhD thesis too but having got to this on Page 2....

ah..but they did admit in the end of the thesis that the way SEER center cultivate (their crops were impressive)and build up their beds for growing..is totally different than how the test were made so it wasn't conclusive..only that the rock dust didn't have any effect in their way of testing.
But what is 'effects' to them as if you look at the charts..the rockdust addition mixes were constantly 'up there' on the top performers.
And looking at the photos of the plants...they were talking about the 'the amount of bulk' that were measured..yes, some potted plants had much more growth on..but to my eyes they don't look the best.
Neither the thesis did test the results with different plant species..it was very limited test even if the quantity of pages from it is impressive.
3 years were maximum time they did the testing..in 'rock scale' that is nothing. I think I bought my first bags 10 yrs ago or so..and I admit first few of them there wasn't nothing to tell...but now, yes, though all the time I have added all sorts into soil so of course I cannot swear hand on bible that it the result of RD...but the one apple tree I mentioned earlier on..it is in its league of its own..others nearby are ok but nothing like that one particular one..I also have several neighbouring trees lost due 'health' problems..and this one is not effected!
But..I'm happy and carry on using it as it is doesn't do any harm neither..nor there is much difference with price of horticultural grit..so if it does good it is bonus, grit I use anyway..

[goodlife]

Oh and to add...(I've got some 'wind under my wings now')..

Soil biology is very complex thing..any changes in it can take loooong time to alter for new conditions/ additions. If one drops great load of rock dust on it..is there the right 'critters' in sufficient quantity to handle the dust? Does the soil have to 'grow' the 'critter' quantity first?..in which case the dust would just sit there before it has chance to 'do' anything..
There weren't nothing done or said for any research of what would be best cultivation method/conditions (or if anything)to get best out of the rock dust. They just searched it almost as 'straight' fertilizer to see what happens rather than 'there is some positive effects shown..why would that be?'. But at least we know now that the way they used it, in their ground conditions and with those plants and although rockdust mixes seem to perform...in their opionion, it is not good enough..

I don't have very scientific way of putting my thoughts across, but I just cannot help all the questions that surfaced up from the thesis...
I'll step down from 'the box' now...

[goodlife]

I'll step down from 'the box' now...

      Not quite yet..

[/quote]

I was reading that organic veg has more minerals in it and my logic for using it was that I cannot expect minerals out if I do not put minerals in.   If I keep taking the crops away where do the minerals come from. 

The land had been used for sheep grazing and presume that they used up minerals.   Perhaps there is a case for using bone meal or BFB.

Yes..that is what is been happening with commercial agriculture for years..they have almost used the minerals up that was deposited from the glaciers during last ice age. I've just read book about all the problems that is caused with the lack of minerals and such in soils...world wide!

With all the rain we have been having, is it time to think about rock dust? I have not used it before. Is it worthwhile? I see B&Q sell it, just under £6 for 10KG.

So getting back to the original post...I would say now..that rockdust doesn't hurt..but it propably is not the answer in short term..you would be better off with good seaweed meal/extract that will deliver lot of minerals etc, much quicker option though doesn't have that long lasting effect...before it does anything..the  soil needs little bit more warmth and activity first. If you can afford to splash out both, dust and seaweed..why not..!?
I bet you didn't expect this much writing about the rock dust effect...

Now I 'step down'...I promise...

[InfraDig]

Many thanks for all the very interesting replies! I think I will go with goodlife's conclusion, if I can afford it! It is sort of where I was with no real backup. I did find the thesis very useful, in particular the different interpretations people put on the results. Thanks again, everyone, for taking the time to explain your viewpoints.

[goodlife]

Me again..

Seaweed extract is around £3 per bottle and will last you quite a while..seaweed meal, that is ground up dry seaweed plants, small amounts are easily bought from 'horse food & stuff' suppliers..again few pounds per bag, bit more expensive to use as it doesn't go very far as extract does and it takes longer to 'work' as it needs to be 'digested' in soil first..it kind of 'slow release version'.
If you go Seer centre site..they will list their rockdust suppliers..they might just be one nearby you..their 20kg bags cost almost same than B&Q 10kg bags..and it is same stuff!
We bought supply to our allotment shed and 20kg bag will cost me just over £7!!

Here you are..some price ideas...

[Ellen K]

Well, the SEER Center is actually in the business of selling rockdust so I'm a bit suspicious of their data - the same way I'd question Monsanto's data about GMOs.  Neither are independent assessors.

Having had a gander on other forums, the consensus is that the benefit of rockdust comes from its liming effect and as you say it also improves drainage as any grit would do.  And as long as it's cheap enough, it may be good value.