Water-retaining gel crystals

Polymer crystals sold to cut watering. Mulch is cheaper, works better, and improves the soil.

What it is

Polyacrylamide or similar hydrogel granules mixed into soil or potting mix, marketed as holding many times their weight in water and dramatically reducing irrigation.

The numbers

• They do absorb a lot of water. The problem is how much of it the plant can actually extract — a meaningful fraction is held at tensions roots cannot overcome.
• Field and container trials have generally found small, inconsistent, or no benefit, especially once soil salts are present — and salts reduce the gel's capacity sharply.
• They degrade over 1–5 years, so whatever benefit exists is temporary.
• Mulch reduces evaporation reliably, costs less, and adds organic matter as it breaks down.

Why it's here

It's a case where a real physical property — these polymers genuinely hold water — gets marketed into a benefit the field data doesn't support.

The catch