Feeling strongly about pumice - well, that sure beats smelling strongly for pumice, Grandpa always said.

My preference - pumice every time, but I'm learning to live with perlite, as pumice isn't readily available, even though BC is part of the Pacific Rim of Fire.

I think it's a matter of accessibility first and preference next, but mostly access - in San Diego, I could get a 30 gallon bag for about $8.

But either are just a component of your soil - what you put in as the remainder is what counts as well; for me, I used pumice to build around, but one can do the same with perlite.

Thanks a lot cactusmcharris for your great input today.

Our modest friend above has even been known at times as the Prince of Pumice (especially to an East Coaster who couldn't find any for herself).

;>)

I'm leaning toward perlite.

Just kidding...

Pumice, never perlite. Over time, my mix has evolved to near perfection as the pumice concentration has increased to about 90%, or more. If I was using perlite, there would be a mess everytime I watered. ;)

pumice++

Pumice, indeed!

Josh

I can get basalt sand readily. Would you guys think that was a good substitute for pumice. Or is it considered to BE pumice in some circles?

between perlite and pumice, i also cast a strong vote for pumice. but i recently got turned onto to coir. now my mix is 90% pumice+coir and 10% organic.

Bri.

I like pumice, perlite is lighter and easier to lift a flat of plants but floats out. Pumice you will not not as many plant diseases, and they don't seem to rot. But is more expenseive. I tried coir but didn't like it as well, the roots start better in coir and the plants seem to love it at first, but it dries out and pulls away from the sides of the pots,
the Huntington Gardens is leaning towards more and more pumice in the mix, it gets more air to the roots, and doesn't pack down, Plants/cuttings don't rot. You need to use what you can obtain, regardless. Norma

I forgot to comment since I DO use both, the problem w/ the perlite being lighter is that it floats to the top & then in a breeze blows all over.

I'm growing indoors in an apartment & always leave my windows open a bit on the bottom, I often come home to bits of perlite all over the floor on windy days, blown off the top of different pots of plants on the windowsills. Not so the pumice, not so light, it stays put. Plants on sill together, the pumice stays put.

Then again, if for things like fluffing up an AV mix, or maybe growing Aralias, I think pumice might be a bit too heavy.

Another drawback of perlite is that it easily breaks down into dust, pumice is a more robust material.

Pumice+++

Years ago i used perlite and it was a mess as others have stated, a few years later I switched to pumice. Now I use more non-moisuture holding grit of varying sizes(maybe 50%) in combination with pumice. What I have found is that this mixture drains more completely, no water collects at the bottom of the container. This combination works great with all this rain were are getting, the water just passing through the pot.

It depends on what your growing.
Perlite is sterilized and has no trace elements in it, and is better for propagation due to a lack of trace elements.
Pumice has high amounts of Boron in it, and depending on where your pumice is mined from it will have higher or lower amounts, but boron none the less

Pumice for all the above stated reasons, though it is really hard to get on my side of the country. And, when I do mail order it..it comes pretty pulverized and is very expensive to ship. So, if anyone knows a reasonable source, I would love to hear it...

turtleman or anyone else - what is the issue with Boron, plants and pumice? Thanks!

Tom

pumice, pick it up on the beach. Pelite floats off, blows away. I do mix it in for some of the tropicals though.
I haven't found a source to buy pumice locally. I've started using a lot of coir, it's easy to get and cheap.
Tally HO!

Karen,

I think I'm accepting a demotion these last few years, as I've been living in the villa of much-reduced circumstances, pumice wise. Can you believe that my mix consists of (mostly) a nursery-bought bag of potting soil, to which I add the twice-and-thrice screened (through 1/2 then 1/4: mesh) sand from the local rock face, and then I'll throw in handfuls of top dressing into the mix? I haven't lost too many plants yet but I imagine there's still some improvements to make. I hope to get a package of pumice from a giving SDCSSer when I am down there next.

Tom,

If you go to a tack shop/ large animal supply or an animal feed lot, they may have a product called 'Dry Stall', which I understand is pumice and isn't pulverized. It may be called something else, but whatever they use to soak up quadruped micturations just might be an answer to your porosity problem.

Juper,

I'd say the pumice proponents have it - you appear to be in an area that has ready access to it.

That person on e-bay was making a killing from me, until as was said above, I could but Dry Stall locally..

Pumice++++

Perlite as was mentioned for a fluffier soil, and in my bark and peat mix..

I take it Turface and Pumice is the same thing? I just looked at some pics of Drystall and it looks/sounds the same as turface. Unfortunately for me...NO one in FL stocks Drystall
:o(...even called the company, no dealerships here.

Pumice/Turface for sure. I only use Perlite...I only use Perlite when I absolutely cannot find the other.

No, pumice is a volcanic rock, Turface is calcinated clay (i.e. a man-made product).

TJ,

What do you use in merry olde Sweden?

Imported pumice (and scoria) is available, even if it (unfortunately) has some clay and fertilizer added to it. Pure pumice is expensive and difficult to find, too few volcanoes here ... The alternative is a freely available type of cat litter made from calcinated "moler" (a Danish rock type consisting of diatomaceous earth and clay), I think it is similar to your "Turface". Very useful. The third option is the balls of calcinated clay called Leca or Hydroleca (maybe it has other names as well?). They don't hold water, but are useful as a light-weight alternative to grit. I have not found any coir yet.

Hi TJ,

Thanks for the response.

I just bought some cat litter (for the seven varmints of Hades) that was quite different than the usual clumping types that we get. My story isn't about the cat or their gifts, but about this cheap version of cat litter - when I saw the ingredients I nearly dropped my socks because it said: Montmorillonite clay and diatomaceous earth. I wonder if it can be used in a potting mix, because the cats and I aren't too fond of it, for different reasons, too.

It depends on if it has been calcinated or not. If it is grey and can be crushed using your fingernails it probably isn't suitable. I have tried these clay aggregates in small amounts, but they disintegrate into very fine clay particles. I have only seen it used for seeds, as in the link below. The type I use is reddish (but not as dark as terracotta pots) and I need pliers to crush it. It also makes a fizzing sound when it absorbs water, just like pumice.
Seven cats? Brave ...

Here is a link that might be useful: Sowing in cat litter

Pumice-more proof is that my Dorstenia gigas switched from perlite mix to a mix I got from a plant imported from Hawaii in that various pumices-red,black..has thrived,regained strength it lost in last years cold wet potted soil.
Like others say-a quality pumice mix is hard to find.

I only use perlite when I need it in large quantities such as big pots. It is very light and useful for aeration.

For small pots, I prefer pumice only because it is a bit heavier and more attractive.

I have never noticed a difference in growth when using one vs the other.

Turface is very different from either pumice or perlite. Different properties, different uses.

They are all very dusty and I would imagine not healthy to breathe in.

x

hello,I have gotten pumice (dry stall actually)shipped from cal.,2 cu.foot cost 63.00 with shipping and savor it for my special plants.I've been buying chicken grit cherry stone(about quarter inch size)now at a farm store near me and it seems suffice. seems like alot of work but I also recyle my pumice,when I repot or a plant dy's in it I wash it in neem oil and reuse.in wisconsin pumice is like gold.someone could drive up here in a semi truck full of the stuff and sell it for triple the price. joe

I've kept an eye out for pumice here in MN, but have yet to find any. I'm interested in using it as a lightweight alternative to granite grit. I've heard conflicting reports, though. Some say that pumice holds very little water much like granite, and others say that it holds lots of water more like Turface. I already have a source for Turface, so I'm not interested in a replacement for that. Can anyone tell me how this stuff compares to granite or Turface in terms of water retention? Maybe I'll just have to order a bag and try it myself.

Joeplant- wow, $63 for 2 cubic feet? that's rough. i've never really appreciated my pumice until i read this thread! how big is 2 cubic feet? how much does it weigh?i'm sure i can ship that much to you for much less. i can get pumice pretty cheap. lemme know if you need more.

Penfold- pumice does not hold water. so long as it's not packed in tight.

Bri.

Bri I lost you, San/ trade maybe. I don't think you will have any thing I don't already have. That cat stuff sounds interesting because of the componets. The clay isn't so, but the other substance is what keeps the mealies away and out of the soil. No pest will X it so it would be great, but use a mask when you use it, you don't want to let it get into your lungs. Add some coarse sand just about 10% only and a pinch of that stuff that breaks up clay, I can't remember the name right now. I had friends that swore by Turface and grew all of their plants in it, it is brown, and looks great in the pots, and does not float to the surface. That is a possibility, I also know a grower that only use pure pumice, but that means that you need to fertilize each week. WE do that any way in the summer after we water, I just wonder if John Trager changes the fertilizer starting at the start of Spring to promote flowering, like perhaps a 3-30-10 I am making up these numbers to make a point. Norma

> pumice does not hold water

Bri, what do you mean? Pumice is very porous and can hold a substantial amount of water for a long time.

Turface is clay and holds water very efficiently. It is used to dry out athletic fields. What makes Turface so unique however is that despite the ability to soak up water, it is a very well aerated substrate. Like pumice and perlite, Turface in a pot is impossible to overwater. And it will not dry out as quickly as other substrates. This is an important quality to preven dessication of fine rootlets during a hot spell or during an extended drought.

x

tjicken- i meant that even though each pebble of pumice may hold moisture in it (becuase its structure is porous), many pebbles of pumice do not hold water between them. so if you pour water through a bag of pure pumice, some of the water gets absorbed into each particle, but excess water drains out of the mixture because of its size (3/8"), leaving a matrix that holds moisture (inside each pebble) but does not leave roots sitting in water. the way i understand it, the higher percentage of pumice in a mixture the more porous it is and the less excess water it will hold. that's what i've been taught and have experienced. but if i'm wrong, please let me know!

Bri.

So you meant that the majority of the interparticle pores are too big to hold water. True for most commercial pumice types I guess, but much smaller size fractions are available too (as observed in soil from cacti i have bought). I was thinking about the total water holding capacity, which of course is far higher than for granite of the same size.

tjicken I disagree with you,when I use straight granite it stays wet alot longer then dry stall pumice and both particles are the same size. joe

I think that the smooth nature of granite or gravel means that the adhesion-cohesion of water is higher than pumice or perlite, which have lots of microporosities. Therefore, non-volcanic rock is more wettable than volcanic rock.

????

x

Yup, this is exactly what I was talking about when I said "conflicting reports" regarding water retention. Lol. Perhaps I'll have to find a bag and do my own porosity test.

Joe, your experience sounds promising. I'm hoping I can use pumice in place of granite without increasing water retention.

Can someone please post a photo of pumice? I'm looking for it but don't know what it looks like. (Vietnamese people might have called it by a "local" name which I'm not aware of.)

Many thanks.

Xuan

As I understand it the point of using porous materials is not to increase/decrease water retention on the outside of the particles, but to provide sufficiently large pores to allow air circulation around the roots while still providing enough humidity (from water stored in the inner pores) to help the fine roots to stay alive.

As I understand it the point of using porous materials is not to increase/decrease water retention on the outside of the particles, but to provide sufficiently large pores to allow air circulation around the roots while still providing enough humidity (from water stored in the inner pores) to help the fine roots to stay alive.

That's the point of using products like Turface or Floor Dry. I'm just wondering if pumice is really in the same category. If you look at xerophyte nyc's experiment here, you'll see that a similar substrate, lava rock, holds very little water. (Thank you for that, xero!) The pores in volcanic rock may be so poor at storing water as to make these substrates comparable to granite, a substrate used for its minimal water retention.

Does anyone know if this coarse Silica Sand that I purchased at a Building supply masonry Co. considered similar to Pumice? In other words I use it in place of granite grit, would this be a good substitute for pumice?

{{gwi:30705}}

Xuan, I've not seem pumice in my area either...but I did pull this pic from the net...hopefully its the right type?

Here is a link that might be useful: {{gwi:469746}}

Red and Grey Pumice (and White Perlite):

{{gwi:9841}}

penfold2,

The pores in lava rock (scoria) are much wider than in pumice, so they are not really comparable (wider pores means lower water retention).

I'll make some experiments tomorrow to find out how much water my pumice, scoria and cat litter actually can store.

TJ,

I can tell you about the liquid retention of cat litter, but you might not like what I'll have to say....

I'm going to get some Dry Stall at a tack shop here, but I simply must get some pumice while I'm in the States and get it across the border, the only problem being security personnel think that it's either explosives or crack cocaine.

Tjicken, that would be great! I haven't been able to find pumice locally, so I'm debating about ordering some. It's kind of expensive though, so I'd like to know how it compares to some other ingredients.

Also, I was thinking about the pore size issue you mentioned. Lava rock has large pores and seems to hold little water, while Turface has microscopic pores and holds a lot. Not sure why that is, but you could be right about that relationship.

Cactusmharris, I am very interested, no matter if I'll like it or not. My cacti like it, and that's more important ...

penfold2
Now it's getting a little more complicated, and it was a long time since I studied this. Larger pores generally drain faster than small due to weaker capillary action. This is something I need to refresh before I try to explain further. Maybe someone else has studied hydrology/soil physics more recently?