Answer: You might be describing a crystalline polymer I have seen advertized lately. It goes by various trade names, one being Hydrosource. You soak the crystal in water, and they swell up to many times their original size. They are often sold to be used as a soil additive--they hold water and so reduce the frequency of watering required. I have now seen them advertized as being a suitable medium for growing.<br><br>I have a personal preference for good old soil. If you use a purchased potting soil, the likelihood of pests contained in the soil is minimal. It's possible that this new polymer would discourage fungus gnats--the little black insects you sometimes see congregating on the soil surface--but you can easily control these with good water management. <br><br>Worm's Way, a mail-order company (1-800-274-9676), sells what they call "Crystal Soil". It comes in a range of colors; this may be what you describe.
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