Rock wool instead of vermiculite?

viktorio on 12/26/2010, 4:51 am

Hello.

This is my first post here, I am a newbie.
Merry Christmas to all and greetings from Bulgaria!

I am planning to start my first SFG soon but I have difficulties finding vermiculite on our market. They sell it small bags at crazy prices - 10 times more expensive than in US!

My question to you is - can I use Rock Wool instead of Vermiculite?
I can find Rock Wool in granules here, in big bags. It is successfully used in hydroponics, as far as I know. Rock Wool pH is alkaline, close to vermiculite, holds water very well, drains well.

What do you think?

LaFee on 12/26/2010, 6:21 am

Hello, Viktorio, and welcome to our forum!

I'm not familiar with rock wool in granules, but if it's all you say it is (and is used in hydroponics) then it should work well for you. The purpose of the vermiculite is to keep the mix light and fluffy and to help hold water...so if the rock wool does the same (and is safe to use in gardens) then it will do the same job.

I'm LaFee, and I'm waiting for the snow to melt here in France, but I think I'm going to be waiting a long time this winter!

Please feel free to ask anything -- there are lots of friendly people here with lots of knowledge to share.

viktorio on 12/26/2010, 7:10 am

Hello, Lafee.
Thanks for your reply.

The rock wool seems light enough - in density it varies between 50-120 kg/m3 usually. Coarse vermiculite varies between 60-80 kg/m3, so I guess those granules should be OK.
Holds water up to 10 times its weight, vermiculite holds up to 5 times its weight, so that should also be OK, I think.

Rockwool is free of pathogens, so should be safe in that regard.
I also found that rockwool absorbs phosphorus which then it releases to plants, so this seems to be beneficial.

Maybe I can try it, due to the difficulties in obtaining vermiculite.

Will be interesting to have other comments too. Thanks for your help.

Odd Duck on 12/27/2010, 9:24 am

Welcome to the forum!

Keep in mind, Viktorio, that Mel recommends just using more compost in the mix if you can't get either the peat or the vermiculite (2/3 compost and 1/3 whichever you can get). He even recommends straight compost where the other components are too expensive or otherwise not available.

I have no experience with rockwool other than having received a few plants that were grown in it, but I found it kind of difficult to deal with. BUT, this was not the granular form, it was the "wool" form. Other than that, I have no wisdom for you, sorry. Wink

Hope you can get it sorted out and happy gardening.

Sharon

viktorio on 12/27/2010, 11:00 am

Thanks, Sharon.

Yes, I am familiar with Mel's recommendation about using more compost instead of the missing component. But as I was looking for another vermiculite alternative I stumbled upon rock wool in hydroponics and found it has similar properties to vermiculite, at least it seems so. That's why I thought maybe somebody has experience with rock wool granules.

I will try to sort it out, sure, I will try with 1 box with rock wool and another - with 2/3 compost. Will see what happens. thanks

ander217 on 12/28/2010, 10:21 am

Welcome, Viktorio.

It's always great to hear from European gardeners.

I have read that vermiculite also absorbs phosphorus and then releases it slowly. I looked up rockwool on the 'net and found this interesting article:

What is rockwool?

It says it was developed in Denmark in the 1970s and is made from heated basalt rock and chalk. It is used as a substitute for perlite, and it will not break down during heavy mixing as perlite or vermiculite will. It is completely inert, so it sounds as though it should work very well in your mix. Keep us posted on the results, please.

I wonder if Mel has experimented with it?

ander217 on 12/28/2010, 10:42 am

I checked out the prices at that site. A 45-lb. 3.5 cu. ft. compressed bale is $57.40. (I'm not sure how much that would make when decompressed.)

How does that compare with your prices?

(According to an online currency converter, if I did it correctly $57.40 = 43.70 euros)

Here we can pick up coarse vermiculite for around $25-$30 for 4 cu. ft. So the rockwool would have to double in bulk when decompressed to make it competitive for us. One ad said it outlasts vermiculite by many years, however.

viktorio on 12/28/2010, 12:12 pm

Thank you, Ander217.

Here you can find vermiculite at crazy prices.
(Take a seat, please).
4 cu. ft. bag costs here 250.30 USD, at the current exchange rate. affraid

There's no way I will buy it Mad

Rockwool with density 100 kgs/m3 costs 111 USD/m3, which means 12.54 USD per 4 cu.ft. (113 liters), that's fine.

viktorio on 12/28/2010, 12:19 pm

It looks like Vermiculite is not popular in my country so prices are too high, unlike Rock wool, where prices are cheaper.

I have no idea if Mel has experimented with Rock wool. I did not find any reference to rock wool in his books. Maybe I should ask him?

LaFee on 12/28/2010, 12:35 pm

Viktorio, I don't know if this helps or not, but I (and the people in England) have found our vermiculite at the building stores, where they sell insulation. I paid about 12 Euros for a 100-litre bag of vermiculite last spring (and am hoping the price is about the same this year, as I'm building a new box!)

If I buy it in the garden department, it's about 8 euros for a 5-litre bag...a huge difference, and a big reward for walking to the other side of the store!

I don't know if they use vermiculite for insulation in Bulgaria, but it might be worth looking, if you haven't already.

viktorio on 12/28/2010, 12:48 pm

LaFee, I checked some of the sellers here, but price is still too high.
Vermiculite is not popular for insulation here. Neither is rock wool, but it is still cheaper.

My last hope is asking the only vermiculite producer here, but I am not sure if he will sell small quantities. Anyway, the fight goes on. I will not give up easily Very Happy

If anybody has had experience with rock wool as an alternative - I will appreciate further comments.

LaFee on 12/28/2010, 1:01 pm

I'm not sure I'd worry about it...if it's being used for hydroponics, you know there are no toxins in it, and it's in your budget, it's less work to just use the rock wool!

Mel says in his book that he doesn't use perlite because it makes him sneeze...no other reason...

viktorio on 12/28/2010, 2:28 pm

Yes, I will give it a try.
Thanks, LaFee.

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