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Hi,

Does anyone know of a source for gypsum containing soils in the USA?

Lots of places sell pelletized and ground gypsum but this material dissolves way too rapidly to be used in a soil mix. So I’m looking either for coarse crushed gypsum or anhydrite or natural gypsum soil. I will use as part of a soil mix for gypsum-loving cacti.

Thank you.

Crushed drywall, sheet rock. It is made out of gypsum.

Thanks—I found this—-this is recycled drywall but it not fast dissolving like the pellets or the powder. And they sell 10 pound bags which can be sent via USPS.

https://www.usagypsum.com/gypsum-produc ... lar-gypsum

Yes, Drywall, or Plasterboard as it's called in the UK is a source of gypsum. However, it might contain other chemicals so do a trial on a spare plant first. As with cat litter etc it's composition may vary since its designed for the original purpose, therefore not all forms may be suitable for plants.

https://www.zerowastescotland.org.uk/co ... board-made

See the discussion here: -

ttps://www.cactiguide.com/forum/viewtopic.php? ... %20Johnson

DaveW wrote: ↑Sun Oct 23, 2022 11:29 amSee the discussion here: -

ttps://www.cactiguide.com/forum/viewtopic.php? ... %20Johnson

I did that post in 2015, and I'll have to correct something I said back then:

Steve Johnson wrote: ↑Sun Mar 22, 2015 5:11 pmAlthough both contain Calcium, gypsum (CaSO4·2H2O) and limestone (CaCO3) are essentially 2 different minerals. The mineral you select should match what a given calciphyte species is growing in natively. With that said, cacti in cultivation do just fine without it.

Wrongo! Thanks to what I learned from MikeInOz in 2020, Calcium is not a natural growth inhibitor as I had believed coming from uninformed people -- in fact it's an important nutrient for growth. As Mike once said, "there's no such thing as too much Calcium", and this doesn't apply merely to the so-called gypsum- or limestone-loving cacti. With that said, there's one thing missing from the equation (and something else I learned from Mike) -- Calcium must be balanced with Magnesium, and the ideal Ca-to-Mg ratio is 4:1. There's nothing magical about gypsum or limestone, so if your cacti need more Ca and/or Mg for optimal growth, you can supplement your fertilizer regimen with a small amount of Cal-Mag fert. Here's a more recent post you may find rather interesting:

https://www.cactiguide.com/forum/viewto ... 54#p394954

I'm coming to the end of my first growing season with Cal-Mag in the fert regiment, and the improvements are pretty amazing.