Issues with Pumice

Discuss repotting, soil, lighting, fertilizing, watering, etc. in this category.
Post Reply
hermesTris
Posts: 5
Joined: Thu Mar 10, 2022 3:06 pm
Location: Manchester

Issues with Pumice

Post by hermesTris »

Hi there. Recently I transplanted some young Cacti from their second to third pots. The first pot was their seedling tray, the second were some small terracotta pots, and these third pots are slightly larger terracotta pots. The soil I used from pot one to pot two was a simple custom mix I made of pumice and coconut coir with a little bit of agricultural charcoal. The ratio was about 65% pumice, 30% coir, and 5% agricultural charcoal. I used a new mix this time of about 45% pumice, 45% volcanic rock, and 10% coir.

The problem was with mix one. As I was removing the cacti the soil was not loose like when I first used it. It had essentially hardened into a concrete like substance. I had to take a pair of pliers and slowly break away the soil. I have no doubt that I damaged the roots of my cacti because some roots were glued to the pumice or to the pot itself. Rinsing the soil with a wash bottle helped loosen things but it was still clumping and the pumice became sticky. I noticed that some of the pumice broke down really easily when I washed it. Some pieces of pumice completely disintegrated while others remained whole.

I'm trying to figure out what I did wrong. Was it the source of the pumice I used?(I'm thinking this was the case. I'm thinking my supplier might have lied to me.) Was it because I mixed it only with coir and a little bit of charcoal?

Has anyone else had a similar experience? I'm worried it will happen again because the pumice I used in soil batch two was the same used in soil batch one.

I have no doubt this is why some of my seedlings seemed to stop growing after I transplanted them from their tray to their first pots. This substance completely stopped all but a few lucky roots from growing.
~Hermes
Average Annual Extreme Minimum Temperature -26.1 to -23.3 Celsius
bbarv
Posts: 217
Joined: Tue Jul 03, 2018 4:21 am
Location: Vancouver, Canada

Re: Issues with Pumice

Post by bbarv »

Sorry to say but it does not sound like a normal pumice, I wouldn’t use this stuff.
User avatar
greenknight
Posts: 4813
Joined: Tue Apr 30, 2013 4:18 am
Location: SW Washington State zone 8b

Re: Issues with Pumice

Post by greenknight »

Pumice doesn't break down like that, I wonder if that was really pumice at all.
Spence :mrgreen:
User avatar
MrXeric
Posts: 559
Joined: Sun Nov 15, 2020 10:31 pm
Location: California, USDA zone 10a

Re: Issues with Pumice

Post by MrXeric »

hermesTris wrote: Fri Mar 11, 2022 8:45 pm ...hardened into a concrete like substance...the pumice became sticky...the pumice broke down really easily...Some pieces of pumice completely disintegrated while others remained whole.
I agree, that is not pumice. Maybe some clay material was mixed into the pumice?
DaveW
Posts: 7374
Joined: Thu Dec 20, 2012 2:36 pm
Location: Nottingham, England/UK

Re: Issues with Pumice

Post by DaveW »

We often use cat litter in the UK but warn people to get the correct type since some are unusable for plants. One often used for cat litter is "Fullers Earth" that is white and breaks down similar to what you describe? It is also one of those used for soaking up oil from garage floors, so there again you need to get the correct type for use for plants since these products are only sold as suitable for the original use intended.

https://en.wikipedia.org/wiki/Fuller%27s_earth
hermesTris
Posts: 5
Joined: Thu Mar 10, 2022 3:06 pm
Location: Manchester

Re: Issues with Pumice

Post by hermesTris »

I want to thank everyone for their feedback. I think I did purchase some pumice, but it was filled in with a contaminant. All I know is I'm never using that supplier again. I purchased it in bulk and have had it in a five gallon sealed bucked in the back of my car. I ended up tossing the whole thing, but I kept the bucket.

I think in the future I'm going to try a new recipe of calcined clay, crushed lava rock, a little expanded shale, and a tiny bit of charcoal, coir, and perlite. I'll figure out the ratio later. All of my materials are intended for plant use.

The good news is this hasn't killed any of my cacti, I used the bad soil for almost a year, but it did severely impact their root growth which explains why the faster growing species I have all seemed to stall in their growth. If there's one thing I learned in the years I've had plants, if the roots aren't growing the rest of the plant won't either.
~Hermes
Average Annual Extreme Minimum Temperature -26.1 to -23.3 Celsius
DaveW
Posts: 7374
Joined: Thu Dec 20, 2012 2:36 pm
Location: Nottingham, England/UK

Re: Issues with Pumice

Post by DaveW »

With some of these materials it is best to sift the fine dust out using something like a flour screen, or one of those sieves sold for Bonsai with interchangeable screens. I sometimes use granite chips that are sold as quarter inch to dust for building purposes, but unless the fine dust is sieved out it sets just like cement.

Probably your countries EBAY also lists them or something similar.

https://www.ebay.co.uk/sch/i.html?_from ... &_osacat=0
hermesTris
Posts: 5
Joined: Thu Mar 10, 2022 3:06 pm
Location: Manchester

Re: Issues with Pumice

Post by hermesTris »

Thank you DaveW. I actually have a set of bonsai sieves. Mine came with 3 different sized strainers. This is an estimate because I don't want to dig it out of my gardening supplies but I believe the three sizes are 1mm, 2-4mm and 5-8mm. I have a spray bottle and a wash bottle that I use to rinse off dust using the 1mm sieve. The other two I use for getting the soil amendment sizes I actually use. I did not have this sieve when I first started and it's been a possible one of the best investments I've ever made for making my own soil.

Regarding my soil amendments, do you foresee any potential issues besides dust? I've heard expanded shale holds water which I'm okay with but that depends on how long it retains water and how well aerated my soil is. I like when I water my cacti for it to retain a little moisture because my apartment can get quiet dry and it allows my cacti and succulents to suck up some water before the air inevitably wicks away the moisture. I just never want them to get soaking wet.
~Hermes
Average Annual Extreme Minimum Temperature -26.1 to -23.3 Celsius
DaveW
Posts: 7374
Joined: Thu Dec 20, 2012 2:36 pm
Location: Nottingham, England/UK

Re: Issues with Pumice

Post by DaveW »

I thought pumice being absorbent it would retain water more than shale since I had not heard of expanded shale before in the UK, therefore I had to look it up.

https://www.gardeningknowhow.com/garden ... mation.htm

The shale I knew was as hard as slate and often used as "hardcore" in the building trade. However evidently it can be "Popcorned" like vermiculite and perlite therefore making it more akin to pumice. In many cases it is not the granular materials holding water themselves that matter, but whether the spaces between them are filled with air rather than water.

https://www.gardenandgreenhouse.net/art ... -solution/

That means the potting soils we use need to drain freely to remove surplus water from around the potting material constituents, even if the individual components themselves retain some. How fast your potting soil dries depends both on the constituents and your climate. We in the UK being in cooler climates need to add more drainage material to get our pots to dry out as quickly as say somebody in the tropics who may do better with a more water retentive potting mix. Most plant roots need air, so waterlogged soils are something to avoid.
Post Reply