transplanting

[keith]

Transplanting Turbinicarpus valdezianus out of clay pot with dense soil into a new lighter soil mix which should work better now that I'm not in the desert anymore. Lets hope they all make it transplanting old cactus doesn't always improve things sometimes one or more can do OK for 6 months and then rot. I won't water them for a few weeks. The little one went into a separate pot. Almost have the entire collection in the new mostly pumice soil now , taking a long time I don't know how a 1000 or more collection can keep up with periodic transplanting ? I have maybe 300 pots at the most ? results after starting this 3 years ago most are doing better some the same and a few rotted which they might have anyway.

it looks like the pumice stays wetter at first then ends up drier after a few weeks. Old soil more linear drying. Because it stays wetter at first I use a thicker layer of gravel to keep the stem from wicking moisture up from the pumice and staining the spines which happens anyway sometimes.

[greenknight]

What causes problems with wet soil isn't the wet so much as lack of air - the water fills up the air spaces in the mix. Pumice holds a lot of air, even as it absorbs some water. It's basically volcanic glass with a lot of little bubbles in it. Water quickly enters those bubbles that have fairly large openings, but has difficulty entering those that have very small openings, it drains away before it enters those cavities. I think this is what you're seeing - the pumice seems wet at first because of all the surface cavities that are full of water, but over time a lot of that water works its way deeper into the pumice granules. It isn't getting dryer, the moisture is just equalizing between the surface and the interior.

Pumice can appear soaking wet and still have plenty of air in it, or it can appear dry but still have moisture trapped inside that the root hairs of plants can access.

[Shane]

Pumice... [is] basically volcanic glass with a lot of little bubbles in it.

On a geological note, it's surprising how much of the content of extensive igneous rocks (lavas, etc) is glass. We tend to think of obsidian as "The" volcanic glass, but rocks such as basalt are also quite glassy themselves

[DaveW]

If you are going to keep plants in the same soil or mineral mix for many years don't forget to leach the pots occasionally with clean water without fertiliser in it to remove any build up of salts in the soil. In the past the old yearly re-potting was as much to remove soils containing a build up of salts starting to become toxic as much as to give them fresh nutrients.

Whilst it is easy in the greenhouse or outside to simply turn the hose on them and let the water run freely out the drainage holes in the pot for a while you can't do that with windowsill collections. However as these usually comprise fewer plants you can either take them outside and leach them or putting them out for a time when it is raining works wonders. Some put them in the bath and pour water on them if they cannot get them outside and presumably a cold shower would work just the same,

https://extension.umd.edu/hgic/topics/w ... ouseplants

Particularly build up of alkalinity from things like tap water if you don't acidify it or use rainwater can often build up:-

https://www.rrm.me.uk/Cacti/Cactus%20an ... linity.pdf

[victoryboxer]

What causes problems with wet soil isn't the wet so much as lack of air - the water fills up the air spaces in the mix. Pumice holds a lot of air, even as it absorbs some water. It's basically volcanic glass with a lot of little bubbles in it. Water quickly enters those bubbles that have fairly large openings, but has difficulty entering those that have very small openings, it drains away before it enters those cavities. I think this is what you're seeing - the pumice seems wet at first because of all the surface cavities that are full of water, but over time a lot of that water works its way deeper into the pumice granules. It isn't getting dryer, the moisture is just equalizing between the surface and the interior.

Pumice can appear soaking wet and still have plenty of air in it, or it can appear dry but still have moisture trapped inside that the root hairs of plants can access.

So how do you avoid the air problem? Going to be re-potting some of mine this weekend with an 80% pumice to 20% potting soil mix. I don't want to mess anything up

[greenknight]

It's not a problem. What I'm saying is that the pumice isn't as soaked as it appears on the surface, it still has lots of air inside.

In any case, after you re-pot you should hold off watering for a week or so to give damaged roots a chance to heal first.