I have read this article about using styrofoam (Polystyrene) instead of Perlite. Is it good to plant Haworthias in 100% styrofoam grains?

The poly's water retention is inferior to that of Perlite, and is closer to that of pumice. The polystyrene balls are easily obtained when you rub a piece of the stuff against a rough surface and all the "grains" break loose.

Setting aside all other issues while processing this stuff, how good will be a 100% styrofoam-based substrate to plant Haworthias? Will the water retention be sufficient for Haworthias?

  • The article is looking at using polystyrene in a potting mix as a substitute for perlite, not using polystyrene on its own as a growing medium - that won't work at all. – Bamboo Feb 5 '19 at 17:34
  • Yes, I noticed that. The idea that it holds water less than Perlite made me think if it is closer to pumice in this regard. However, I was advised to steer away from it. – Christmas Snow Feb 6 '19 at 8:20

Because polystyrene is partially or mostly water resistant it doesn't hold water like perlite or pumice (lower porosity per the article). Water retention for polystyrene is 10% that of perlite.

The article doesn't read like a ringing endorsement of polystyrene. It also doesn't address using it alone as a potting media, as you asked. It's always mixed with something else (peat!!!!) in their tests.

So, to answer your question, it probably won't kill your Haworthias immediately, but it's not an ideal solution.

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