Pumice as a Growing Medium
Pumice is a volcanic rock with many pore spaces. This alone makes it a fantastic growing medium because it creates a lot of aeration for roots. Roots absolutely need oxygen to thrive. Some plants need less but usually all plants thrive with a highly oxygenated root zone. There are plenty of resources explaining in this in more detail and you can find them by doing a simple Google search on oxygen in the root zone.
What’s interesting about pumice is that it also can hold water in those pore spaces at the same time it’s holding air, too. This couldn’t get better in terms of a growing medium. You’re talking about having a medium that holds both water and air simultaneously. These are the two things plants need the most.
Pumice doesn’t hold onto nutrients well but you can overcome that by feeding with a fertilizer like DG Foliage Pro at every watering. I usually recommend this fertilizer because it has everything a plant needs and it is already dissolved in water, so you don’t need to worry about leaving any fertilizer residue and causing burns to the plant.
I’ve found that to be the case when using the Mittleider gardening method. On its premise, the Mittleider method is a superior growing method. However, too often the fertilizer is still around even after a good soaking. I’ve had some sensitive plants get burned from the residual fertilizer. Combining the Mittleider method with Foliage Pro will make this risk obsolete.
Above is a Calathea grown in only pumice rock. I put the pot, in which it’s growing, in another pot so I could bottom water with Foliage Pro. Calatheas are supposedly notorious as difficult and fussy. I’ve only seen this plant thrive since changing over to 100% pumice.
I also have a banana that has grown really well in just pumice. You do have to keep an eye on watering but I use pulse watering techniques so my plants never dry out. Pulse watering with pumice works really well; almost so well it’s hard to believe.
Another important thing to consider about growing mediums is keeping organic ingredients out of them because they are decomposing and they can promote root rot. If I’m growing anything perennial or long-term, my growing mix will have nothing that can rot. If I’m growing annuals or short-term plants, then I’ll add compost but it is never more than 10-15% of the medium. Anything over that will promote root rot.
