Geohintonia mexicana mix

[Saguaro123]

I need to repot my Geohintonia mexicana, and I found out they need a higher mineral content. Is a mix with 50% gypsum and 50% regular cactus mix (1/2 pumice, 1/8 lava rock, <1/8 peat moss, 1/4 super soil) recommended?

[Steve Johnson]

I need to repot my Geohintonia mexicana, and I found out they need a higher mineral content. Is a mix with 50% gypsum and 50% regular cactus mix (1/2 pumice, 1/8 lava rock, <1/8 peat moss, 1/4 super soil) recommended?

Not sure why you would need to make it that complicated. I have a Geohintonia in pumice/DG mix (coarse aggregate, I sift out the DG "play sand" fines first), and it's growing well for me thus far. So-called "calcium lovers" in the wild grow where they do because they're adapted to alkaline soils that won't support other plant life. Doesn't necessarily mean that these cacti will exhibit unnatural growth if we don't supplement their potting medium with gypsum or limestone. Just my 2 cents, so it's really up to you.

[DaveW]

Geohintonia grows on gypsum for the reason Steve says. I have read that Geohintonia's will not tolerate limestone in the potting mix (unlike Ariocarpus etc). People often confuse the two thinking plants growing on either gypsum or limestone means the plants require an alkaline soil, whereas those on gypsum may not.

The fact they can grow well in different potting mixes means they probably don't need gypsum, but it will do no harm adding it in small amounts. However I have not actually tested whether they actually are averse to limestone in the mix, only read the following:-

"Geohintonia loves calcium, but if limestone is added to the potting mix the plant will simply die. It seems not to tolerate the alkaline reaction of limestone. In nature this plant grows on gypsum which generates a neutral pH, or, depending on the other impurities found, even slightly acid"

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[adetheproducer]

I got my one in a mainly mineral mix wth both limestone and gypsum(alabaster chippings), red granite chippings and then some loamy soil. It grows quite quickly this mix and it drains quickly too.

[Saguaro123]

Thanks for your input everyone!

However, what is the proportion of your mix, adetheproducer?

[adetheproducer]

about 15% limestone, 15% alabaster(gypsum), 40% red granite chippings and the rest loamy soil, but I would stress the ratios are not fixed, this works for me in my local temperature, humidity and watering regimes.

[CactusFanDan]

I grow my Geo's in the same mix as all my other cacti and they're doing great - 20% 'organics' and the rest 'mineral' with some additives. Overall an acidic mix with no limestone or gypsum. I don't like to waste my time making fanciful soil mixes. They're not as difficult as they're passed off to be as long as you apply common sense (if it doesn't look like it's thirsty, it probably isn't).

[Saguaro123]

I decided to pot it in my regular cactus mix without the gypsum. Thanks for all your feedback!