perlite growing medium

[Chez2]

I went through a Perlite phase maybe 20 years ago and have now gone back to JI/grit because the addition of Perlite seemed to offer no advantages. Used as a major part of the compost the plants in it become top heavy. I am anti top-dressing (particularly dangerous with all the winter-growing material that I have) so having all this white floating on the top of pots is not great. Also it looks horrendous when you throw your old compost out onto the garden. The most important problem is that you should not use Perlite dry because of all the dust that you certainly do not want to breath in. I did continue to use Perlite for seed and cuttings for a longer period but have now given that up too because I get better root systems by having 50% Meadowview potting grit Eco in the compost.

I find quite the opposite to you; using perlite makes pots much lighter than using grit. The density of perlite is much less than that of grit and its also supposed to let more air in to the pot. I use it on a lot of my plants in tubs, not just succulents or cacti. I haven't done any root comparison trials, everything seems to grow well enough.

[KarlR]

I went through a Perlite phase maybe 20 years ago and have now gone back to JI/grit because the addition of Perlite seemed to offer no advantages. Used as a major part of the compost the plants in it become top heavy. I am anti top-dressing (particularly dangerous with all the winter-growing material that I have) so having all this white floating on the top of pots is not great. Also it looks horrendous when you throw your old compost out onto the garden. The most important problem is that you should not use Perlite dry because of all the dust that you certainly do not want to breath in. I did continue to use Perlite for seed and cuttings for a longer period but have now given that up too because I get better root systems by having 50% Meadowview potting grit Eco in the compost.

I find quite the opposite to you; using perlite makes pots much lighter than using grit. The density of perlite is much less than that of grit and its also supposed to let more air in to the pot. I use it on a lot of my plants in tubs, not just succulents or cacti. I haven't done any root comparison trials, everything seems to grow well enough.

Terry writes that the plants become top heavy as a result of the amount of feather light perlite in the soil. I'm guessing you misread?

I've used perlite and vermiculite quite a bit before and come to the personal conclusion that they work best for seedlings. I don't like the perlite dust so I will probably stop using it.

I much prefer crushed lava or pumice. They serve the same role, only better in my experience.

[Terry S.]

Questions have been asked about the various mineral substrates that we are using. So here is a brief guide, but note that they will all have a requirement of energy for heat treatment (except pumice) and for transport across countries.

Moler (syn, Seramis, absorbent granules, hard cat litter) - a diatomaceous earth (ancient fossilized microfauna) mined in Nordic countries and heat-treated to form the granules.

Akadama - very similar, but it is a granular clay-like material that is surface mined in Japan and then baked. Hard grades (the most expensive) are supposedly best.

Pumice - rapidly solidified frothy glass that was emitted from volcanoes during eruptions. It is mined in various grades and sizes and is presumably a product which is a renewable material in view of the fact that volcanoes keep erupting (Scoria is similar but denser).

Perlite - from another volcanic glass, but rather than the "bubbles" coming from gasses expanding in the glass during an eruption, the solid glass contains water which explodes like popcorn when it is heat treated.

Vermiculite - mica that is heat-treated to cause the flakes to separate such that they become light with lots of spaces. I am not sure where it is mined commercially but I know that small-scale mica and pegmatite mining on quartz fields in the Northern Cape has certainly destroyed a few succulents.

The feature of all these materials is that they contain a solid matrix with many spaces in between. These can hold oxygen and/or water that plants need around their roots. Some people are upset about peat being dug out for horticulture, but aren't most of these other materials similarly destructive to the environment?

[Chez2]

I went through a Perlite phase maybe 20 years ago and have now gone back to JI/grit because the addition of Perlite seemed to offer no advantages. Used as a major part of the compost the plants in it become top heavy. I am anti top-dressing (particularly dangerous with all the winter-growing material that I have) so having all this white floating on the top of pots is not great. Also it looks horrendous when you throw your old compost out onto the garden. The most important problem is that you should not use Perlite dry because of all the dust that you certainly do not want to breath in. I did continue to use Perlite for seed and cuttings for a longer period but have now given that up too because I get better root systems by having 50% Meadowview potting grit Eco in the compost.

I find quite the opposite to you; using perlite makes pots much lighter than using grit. The density of perlite is much less than that of grit and its also supposed to let more air in to the pot. I use it on a lot of my plants in tubs, not just succulents or cacti. I haven't done any root comparison trials, everything seems to grow well enough.

Terry writes that the plants become top heavy as a result of the amount of feather light perlite in the soil. I'm guessing you misread?

I've used perlite and vermiculite quite a bit before and come to the personal conclusion that they work best for seedlings. I don't like the perlite dust so I will probably stop using it.

I much prefer crushed lava or pumice. They serve the same role, only better in my experience.

Ah yes, thanks. I should learn to read slower so I don't miss anything. I did think I read heavy not top heavy. I use thick decorative pots so mine wouldn't become top heavy.

[colser]

Thanks for the details Terry

[Herts Mike]

Yes, excellent details Terry.