If you’ve ever bought commercial potting soil, chances are wetting agents have been a component in the soil mix. Wetting agents help soils to absorb and retain moisture. In this week’s tip, we’ll cover what wetting agents are, where they are used, and why some gardeners like to include it as part of their potting soil mix.

Wetting agents fall under the category of surfactants, just like detergents/soaps and emulsifiers. Chemically, they are typically organic compounds with hydrophobic (water hating) and hydrophilic (water loving) groups.

Practically, wetting agents lower the surface tension between a liquid and a solid. If you’ve ever had soil dry out for extended periods of time, you’ll recall how water would have pooled at the top and taken a long time to absorb into the medium. That is because when certain growing media when left to dry over extended periods of time, they can become hydrophobic and repellent to water. So potting soil mixes can become hydrophobic when left sitting on the shelf or if left to dry in the pots.

Think of how quickly your potted plants dry out in the summer, especially if you forget to water them or are away for extended periods of time. So when it comes to potted plants (and very sandy soils), wetting agents can improve water retention and water absorption in the soil.

Wetting agents come most commonly as a crystal. They minimize the need to water as frequently and allow you to use less water. It does this by increasing the water holding capacity of the soil, allowing plants to go longer between watering. It does not change the amount of water a plant needs.

Wetting agents will eventually break down over time by soil micro-organisms. Like all chemicals, care should be taken as they can interfere with the life cycle of aquatic organisms if overused and let to runoff into lakes and streams.

At YUF, our philosophy is not to use chemical products where necessary. That’s why you won’t find wetting agents in any of our soil mixes. If you’d prefer not to use chemical wetting agents, here’s what we recommend.

  1. Choose sub-irrigated containers that allows water to slowly and thoroughly penetrate through the soil medium.
  2. Add mulch to keep soils moist and slow down the water loss from evaporation.
  3. Water more frequently if you see the soil drying out quickly and on a regular basis.
Cover Image by Karen Jackson, used under its Creative Commons license.

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