Vermiculite and water-retaining

Last year I posted that I was unable to get vermiculite here, so I bought local pumice instead in the hope that it would work for me. I wanted to compare the water-retaining of the two and see if I was on the right track.

Belfrybat was kind enough to post me a bag of vermiculite and I finally got my act together and did a little experiment.

I took a litre of each material, dried it in the oven for 4 hours at 90°C, and weighed each sample. Then I soaked each one for 2 hours, poured off the excess water, and reweighed it.

The vermiculite held 396g/l of water, and the pumice held 231g/l.

For the non-metric folk, the numbers are about the same in g/l and oz/cu ft. This means that each cubic foot of vermiculite which you add will hold about 25 lbs of water.

I'm disappointed that my pumice only holds about half of that amount but as it is all I've got then I'll just have to stick with it... unless, now here's an idea, how many forum members are there? If you all sent me a small bag of vermiculite... (just joking)

Nice experiment. And even though pumice doesn't hold as much water it still holds quite a bit.

I would have to hand deliver my small bag of vermiculite. Iceland is gorgeous and I tell my husband that it is the ONE place I would visit again in a heartbeat.

Come on over - but if you come this week bring a snow suit because we have more now than all winter!

How very cool! Thanks for sharing your results with us!

Sure one holds more than the other, but did you try and test how slowly they realease the water? Maybe there's a difference?

Neat experiment, either way.

BackyardBirdGardner wrote:Sure one holds more than the other, but did you try and test how slowly they realease the water? Maybe there's a difference?

I did try, and over 4 days the vermiculite lost about 100g of water and the pumice 60g.

I just left the samples sitting in identical plastic jugs, I'm not sure how meaningful that is because in Mel's Mix then the water must be pulled out by some sort of wick-action. And I'm not sure if it is good or bad to give the water out faster? It would be bad to hold onto it and not let it into the compost-peatmoss. And also bad to just let it all go quickly.

I'm just looking where I might buy it in the UK (my husband asked me if I would like a spring holiday and I bet I could fit 100 l of vermiculite in my suitcase if I try! )

I can see it now. Take a suitcase full of clothes and come home with a suitcase full of vermiculite.

Wouldn't have to worry about the weight limits!

elliephant wrote:Wouldn't have to worry about the weight limits!

was just thinking the same thing.

elliephant wrote:Wouldn't have to worry about the weight limits!

Maybe not, it is light stuff. 1 litre of vermiculite weighs just over 100g so a 100 l sack would be under 15kg for sure and I get 20kg allowance. This could actually work out though I'm not sure what the customs people would make of it... and my husband is not famed for his sympathy towards gardening projects. Perhaps I should look into posting it instead?