Pumice

[Greenmanplants]

Dave,

Here is a pot of C. kentuckiense which have been grown in Biosorb for 2 years, hopefully a few will be at flowering size now as these are 4 years old going into their 5th year.  Biosorb, although used as an animal litter is also used as a turf conditioner for sports grounds as I mentioned above, this is not available in Supermarkets and you will only find it in Wholesale Agricultural/landscaping outlets. 

This is about 1/5 the price of Seramis and does very well. It is an agricultural product and will not kill your plants having a secondary use as animal litter.  However the pumice above looks very good as well and I am going to source some.   

[Slug Killer]

Hi, I'll have to try some Biosorb as it looks good stuff. I'll look at my Avoncrop CD and see if they sell it. My Cyps are coming on fast now and they have forcast a mini heat wave this weekend so will have to make sure they stay OK. Some pics so far this year. The first one has some leaf damage/discolouration as the sun got it.

[Martin Baxendale]

Thanks for the Avoncrop mention, John. Had a look at their website and they have all kinds of interesting growing media to order by mail order - including what looks like good quality composted bark in different grades as well as Grodan granules that sound like a Seramis type product and all kinds of speciality fertilisers, composts, square pots, trays, etc.

[Slug Killer]

I've ordered from Avoncrop before and they are very good. The Melcourt Potting bark they sell is great stuff as it's clean and small, ideal for Pleione etc. I did order a bag of Melcourt Orchid bark and found the chunks far to big for my needs but useful for filling up space in large pots.

[Giles]

The RHS are good at sourcing stuff if you ask. When I wanted pumice, they put me in touch with Viresco, Thirsk, N.Yorks
-the company sent me samples of different grades of pumice before I placed an order, which was really helpful. Admittedly
after a few trials of different mixes I settled on a Seramis based Cyp compost (as used by Ratcliffes) and haven't killed a
Cypripedium since!!!

[Anthony Darby]

Dave, those spotted leaf cyps look very healthy. Are they under cover and how do you water them?

[Slug Killer]

Hi, all my spotted Cyps are undercover in a cold frame. I water from the top until they come in to leaf and then place on a capillary mat with a wick going over the side of the pot to get some moisture in the top. They are grown in mainly pumice with a little John Innes No1 and fine bark in the top half only. I do water very carefully now and again from the top, taking care not to wet the leaves. All my Cyps are now in pumice. Next year when re-potting I will probably run the capillary wick inside the pot from top to bottom. The two in he photo below will be open any day now.

[Rodger Whitlock]

Pumice is also an excellent growing medium for some of the trickier alpines. Plants I have growing in pure pumice include Kelseya uniflora, Nierembergia patagonica, Weldenia candida, and a couple of the South American rhizomatous oxalis. If it were cheaper and more readily available, I'd use a great deal more of it.

[JohnnyD]

Just picked up this thread and may have an idea which could work.
One of the main uses for pumice is in the manufacture of building blocks - the 'fair face' version of 'breeze blocks'.
Deliveries to the manufacturers are made in huge truck loads, and are a mix from dust up to 15mm or so.
Try asking your local block maker (they are seldom far from their market) if he has it - a bucketful or two would cost very little, and sieving it for the right size quite easy.
See what else he has too, all lightweight blocks use inert granular materials which could be used in composts.
John

[Slug Killer]

Nice idea but it's not horticultural grade pumice, I have already tried it from a local supplier in Shropshire. The pumice used in building blocks has been kiln dried to very high temperatures and produces a hell of a lot of dust and will crumble very quickly unless compacted in to a light weight block (brick). Generally the pumice used for horticultural use is pre-washed pumice GRIT and is very different from a pumice stone. Some of the smaller kiln dried stuff (1-3mm) is pretty good for very small seedlings like Cyps bought in from the like of Phytesia but needs drenching in water to remove most of the dust.

[JohnnyD]

I have never seen kiln dried pumice used in blocks. Generally it is stored outside in heaps and drying would be a waste of cash!
I do agree that there are very different grades of pumice depending on the source - but for blocks they are generally shipped in huge quantities direct to the block makers.
Suggest you try a different block maker - Good Luck!
John

[Slug Killer]

Perhaps your right it's just what I was told at the local brick maker down the road. He might have meant it was kiln dried after or during the blocks making? To be honest I'll stick to buying horticultural grit grade stuff and not go for any cheaper options (like cat litter instead of seramis) as my plants are worth to much money and I'd hate to loose them just for the sake of saving a few ££££. I'm all for saving as costs are high these days but I'll be the coward on this occasion and let someone else try it out first

[Rodger Whitlock]

The discussion in this thread makes me think that the word pumice is being used for two kinds of rock with quite different horticultural properties.

The pumice I use for plants is very light and can be described as a mineral froth. It forms when magma is expelled from a volcano very quickly, and the dissolved gases in the magma expand when it enters the lower pressure of the atmosphere. Being porous, this kind of pumice retains moisture very well.

There's another kind of pumice sold in blocks for sanding down the rough skin on one's feet and similar purposes. It might do as a grit in potting composts, but I doubt it is sufficiently porous and water-retentive to do well as a growing medium. I think this kind may form by consolidation of beds of very fine volcanic dust under the action of water.

In addition, there is volcanic ash. It's vesicular, but lacks the very fine porosity that makes horticultural pumice so useful. Doesn't hold moisture at all well, and useful only as the gritty component in soil mixes. I've seen red and black forms of it sold in bags for use as an ornamental top dressing on flower beds. Not very ornamental, to my eye!

[Slug Killer]

Black and red as ornamental, yuk (my opinion).

Below is a picture of what I use both as a mix and on its own for some young Cyps. It holds 15-20% of its weight in water when drenched. My spotted Cyps used to suffer before I started using this mix but seem very healthy now as it bulks up the mix and provides better drainage. By using it on its own for the last inch I no longer suffer with neck rot early on in the year. This was sold to me as horticultural pumice grit and I've been very pleased with it so far. Green leaves in the background as just a few of my Pleione.

[derekb]

Dave, I grow Disa as well as other Hardy Orchids but I am not happy with Pumice I will stay with
Dyna-Rok as I was telling Anthony this has far better capillary action it is virtually indestructable when it comes time to repot I wash it through give it a good soak in Milton disinfectant rinse it and if you are lucky enough to have a wife at home send her to the shops and put it in the Microwave for a couple of minutes and it is back ready to use. This is a USA product so I think there will be other users out there.
I forget what I paid for Pumice but Dyna-Rok is £25.0 for 40 ltrs + £10.50 postage.
I am not sure about saying the retailers name on here but if anyone is interested send me a PM.
They also do other Orchid fertilisers.

Derek