polymer crystals...

A very good and quite cheap substitute for these are the innerds of baby diapers. I have used these for years in the bottoms of pots and baskets.

In places where I know the pots will need an extra boost of moisture, I leave them as is, opened out and I place the plastic liner side to the bottom of the pot.

I stay away from any of them that are highly perfumed. The only time they were too wet, for too long, I had to pull them out from beneath the root ball of some Pentas in a window box.

Don't cover the drain hole with them either.

ThonotoRose