Pumice vs perlite

[keith]

I use pumice sold as DRY STALL for horses you put it in the barn on the floor and it absorbs horse urine . its smaller and most of it doesn't float.

Perlite floats in water so it can float out of your pot depending on how you water. I think it works fine though I used to use it.

[jp29]

As we all are moving to more mineral mixes ........
Rachel

I am not ..... I have had about 40% of my cacti in a strictly mineral mix (for the past five years) and the remainder in a (approximately) 30% peat moss, 30% composted forest mulch, 40% coarse pumice - mix that I have used for the past sixty or so years (modified several times). The latter mix produces healthier, more robust plants for me.

[Spikylover]

Limestone chippings are also probably cheaper from your local builders merchants. Make sure they are the size you want though since often several sizes are stocked, some too large for our use. Unlike the ones in the link below I think mine were only about 10mm in size. However whether you really need limestone chips for cacti is debatable.:-

https://www.travisperkins.co.uk/Limesto ... k/p/996263

Hold on. I thought limestone is very bad for south american cacti and wouldn't it erode and cause lime deposists?

[Spikylover]

As we all are moving to more mineral mixes ........
Rachel

I am not ..... I have had about 40% of my cacti in a strictly mineral mix (for the past five years) and the remainder in a (approximately) 30% peat moss, 30% composted forest mulch, 40% coarse pumice - mix that I have used for the past sixty or so years (modified several times). The latter mix produces healthier, more robust plants for me.

Glad to hear from someone with such an experience! I am usimg 60 70% grit and compost and havung great results but it stays a little wet on overcast or early spring days which worries me.

[Spikylover]

Not to be ingrateful for all the replies which i really appreciate but i still haven't figured out the advantage of pumice over perlite that justifies the cost.

[DaveW]

Some use limestone for N. American cacti that grow on it in the wild, but most S. American cacti do not grow on limestone, a lot grow on disintegrated granite and quartz, particularly in Chile.

As I said previously:-

"However whether you really need limestone chips for cacti is debatable."

Marlon Machado, a Brazilian Botanist, maintained that cacti growing on limestone or alkaline soils only grew when they received acid rain and stopped growing again when the substrata turned the water alkaline. I don't know if that has been scientifically tested, but some have done experiments with alkalinity and cacti:-

http://ralph.cs.cf.ac.uk/Cacti/Cactus%2 ... linity.pdf

[cactidan]

As we all are moving to more mineral mixes ........
Rachel

I am not ..... I have had about 40% of my cacti in a strictly mineral mix (for the past five years) and the remainder in a (approximately) 30% peat moss, 30% composted forest mulch, 40% coarse pumice - mix that I have used for the past sixty or so years (modified several times). The latter mix produces healthier, more robust plants for me.

I am firmly with you James, i have seen some people do well with "mineral" mixes but it doesn't suit my situation and I have seen poorer results when I have experimented with it. So I am not moving over either.

I dont really know much about pumice I'm afraid, never used it in the 20 odd years that I have had cacti. I have tried perlite before and I didn't really like it as did find it wouldn't stay evenly distributed throughout the soil mix. Do not use either now, just grit, what is known as john innes 3 compost (might be a stretch to really call it that) and a type of cat litter.

[DaveW]

For our American readers the Brits call potting soil, potting compost, not meaning potting plants solely in the rotted down products of a compost heap. However that is possibly how it originally got it's name, with the old gardeners before the peat days adding some to their potting soils.

Yes, John Innes composts in the UK are not what they used to be, often because using peat is now frowned on by the conservationists. I have even seen "peat free John Innes compost" sold, which is a bit of a nonsense since peat is an integral part of their mixes.

I bought some JI ericaceous compost and they had substituted poorly rotted garden waste for the peat, therefore I had to just throw it on the garden as unusable for potting. These days if you want the original recipe you may have to make your own.

The only difference between JI numbers 1 to 3 is simply the amount of fertiliser added. Also these days a modern balanced fertiliser is usually added in commercial mixes rather than the old JI recipe. Here are the original recipes:-

https://www.gardeningdata.co.uk/soil/jo ... _innes.php

The reason pumice is not usually used in the UK Dan is it is too expensive, having to be imported. You can get it on EBAY, but delivery too is expensive.

[teo]

The reason pumice is not usually used in the UK Dan is it is too expensive, having to be imported. You can get it on EBAY, but delivery too is expensive.

That is a bit strange. Pumice is fairly cheap here (Sweden) and it's definitely not produced here but in (volcanic) Iceland (most of it I think). That should be about the same price to import to Britain.

[Grimm]

And the only cat litter i can find is crushed limestone.

This is probably Zeolite rather than limestone, which is potentially useful for cacti as it holds water and nutrients. I'm experimenting with it for my epiphytic cacti at the moment.

Similar to others, I don't like the way perlite moves around in the soil so don't use it for that reason. It is also quite expensive in some UK shops (I haven't shopped around, so it may be available cheaply).

[DaveW]

It is expensive in the UK due to transport costs, whether that is in the price or charged extra for Teo compared to other potting ingredients you can obtain locally:-

https://www.ebay.co.uk/itm/Horticultura ... SwxX1Zx-Iq

https://www.ebay.co.uk/itm/Pumice-2-3mm ... SwbihZ03qB

https://www.ebay.co.uk/itm/Pumice-2-3mm ... SwbihZ03qB

[DesertSun]

I have no experience with perlite in cactus soil mix, but I do have in many houseplants. It can make a heavy soil that could cause root suffocation in days, livable for a plant. If you use it in a plentiful percentage, I used it in a 50 % for some heavy soil in a couple of pots, it does make a difference. On the other hand, as members have already stated, it is so lightweight it will eventually start coming to the top. On the other hand pumice is great for keeping some even moisture and provide aeriation, but it too breaks down over time, and the dust becomes like a cement at the bottom of the pot. Perlite on the other hand does not stay moist. Another minus of the perlite is the appearance it gets with time, it gets dirty looking, so if there is enough in your soil and comes up gradually, you will have an aesthetic problem if you mind about aesthetics. Also, when you have perlite in your soil, it would be difficult to make a decent root examination, it gets so confusing for example trying to distinguish root mealybugs from perlite.

[7george]

Well, the lightness of the perlite can be fixed by suppressing the soil by a layer of top-dressing of rocks or clay pebbles. Regarding pumice: it is maybe better but hard to find and expensive outside USA. Even the biggest mine and plant in Idaho is almost "near by" for me the shipping cost is unacceptable.