Pure mineral soil mix?

[Echinocactus123]

Hello everyone,

Recently I have found a few issues with my current soil mix, My especially sensitive cacti aren't doing too great in a part organic soil mix. I bought a Strombocactus disciformis a while back in a pure mineral mix, it drained very well, it flowers frequently and its just overall cleaner to use. I would love to use a pure mineral mix for my other cacti but I really don't know what to use. Are there any growers who can recommend a good recipe?
Thanks for any replies.

[Phil_SK]

I recommend whatever your strombocactus is in if it works for you. I'm always uncomfortable recommending a soil mix, as what works for one grower mightn't work for another. My repeated failures with plants in JI soils demonstrates this all too well.
That said, I've been using 1:1 grit and moler since 2014 and it works for me. My top tip for making radical soil changes is to remove every last scrap of the old soil even if lots of roots are lost in the process. If the damage is significant, let it dry off unpotted and then pot into a small pot.

[Pattock]

I use perlite:moler 1:1 for most of my succulents, but I don't grow cacti so just ignore me. My Dracaena draco is in pure perlite and loving it.

What fertiliser are you using? Most of Devon is very soft or moderately soft water. If you are using Chempak or other hard water fertilisers then you could have a calcium deficiency. Soft water fertilisers are available. You also have to be sure of providing the full spectrum of nutrients in a pure mineral soil.

https://www.southwestwater.co.uk/advice ... de-search/

Happy Birthday recently?

[Echinocactus123]

I use perlite:moler 1:1 for most of my succulents, but I don't grow cacti so just ignore me. My Dracaena draco is in pure perlite and loving it.

What fertiliser are you using? Most of Devon is very soft or moderately soft water. If you are using Chempak or other hard water fertilisers then you could have a calcium deficiency. Soft water fertilisers are available. You also have to be sure of providing the full spectrum of nutrients in a pure mineral soil.

https://www.southwestwater.co.uk/advice ... de-search/

Happy Birthday recently?

Thanks for the happy bithday And the info on fertilizers, I'll try to find a soft water fertiliser to use. Do you sterilize pure mineral mixes? When I used a JI mix I always microwaved it.

[MikeDom]

I've moved away from JI, moler, grit and sand combinations and have potted all my cacti in pure lava rock, between 3 and 8mm in size. I grow mainly tuberous rooted cacti, somewhere approaching about 80 plants some large and old. Other succulents are in a different mineral mix, except for Asclepiads which do really well in pure lava rock.

I have noticed that cacti grow much better in pure lava rock and rotting doesn't happen often. I have been watering since mid-Jan - I wouldn't do that in a JI mix, and the plants have responded well. The excellent aeration of the roots probably helps although the lava rock can sometimes set like concrete with smaller particles, but the plants often live in a similar substrate in habitat, and a slight squeeze of the pot breaks it all up again. The lava rock contains high levels of iron, magnesium and other minerals - if you're growing Pachypodiums note that they need high levels of iron [Walter Roosli}.

If you suffer from mealy bugs, you will find that they will work their way down the roots into the pot which they won't do with a compact JI mix. On the other hand , if you soak the pot in a contact/systemic pesticide it has more chance of killing any pests in the pot by contact. Drenching the pot takes seconds and only a small amount of water is absorbed by the lava rock, the rest runs off.

It works for me, is reusable and is frost proof. You have to fertilise, and Chempak Low Nitrogen or High Potash is suitable - I won't give any recommendation for levels. As Phil says, what works for me might not work for you, but having used pumice and coir combinations also, I've ended up being entirely satisfied with pure lava rock.

I'm providing observations, not recommendations.

[Pattock]

You would think you wouldn't have to sterilise it because it is mineral and some of it is made at over 800°C, right? That is what I thought until I kept getting a weird mildew on seedlings in perlite. It depends where it has been stored, I think.

I simmer mine in boiling water for about ten minutes then leave it to cool down for a few hours still in the water. That might not suit all minerals. I don't use my landlord's microwave for gardening. I have a bag of pumice I should open soon.

[gerald]

Boiling water will kill live bacteria but not their spores. Same with fungi.

'Sterilising' soil is somewhat futile because as soon as it's out of the 'steriliser', it's not in a sterile environment and any airborne spores (there are many) will just infect it again.

Good quality, healthy soil or other media will not have an abundance of pathogens anyway, and you may well be destroying the beneficial ones, which could create an opportunity for the bad ones to take over.

[esp]

Boiling water will kill live bacteria but not their spores. Same with fungi.

Bacteria do not reproduce via spores. Boiling (although perhaps not some rather diluted exposure to boiling water) will generally kill most bacteria.

Boiling will kill many fungal spores too. Higher temperatures and/or longer times will kill more spores.

Microwaving damp potting mix for a few minutes is likely to achieve a much better degree of sterilisation than pouring boiling water over/through pots.

[gerald]

Bacteria do not reproduce via spores. Boiling (although perhaps not some rather diluted exposure to boiling water) will generally kill most bacteria.
[/quote]

No they don't reproduce by spores (I didn't say they did ) but they can form spores (endospores) in response to adverse environmental conditions as a survival mechanism and will be present as such before, during and after boiling water is used to kill them

Which is why an autoclave is used to sterilise rather than just boiling water, and why boiling water isn't always sufficient