Soil So Dry it Repels Water

Have you ever seen soil so dry that it repels water? This often happens with bagged potting soil. If you fill up a pot with really dry potting soil and try to water it, the water seems to bead off the soil and run out of the holes in the pot – like rain on a freshly-waxed car. The soil has become “hydrophobic” – it literally repels water.

When potting soil is really dry like this, it’s best to first soak it in water for a while in a bucket or wheel barrel.

With the extended drought here in Fayette County, the soil in my idle in-ground gardens have become hydrophobic. Water puddles on top of it and runs off until it finds a crack in the ground.

On a microscopic level, soil becomes hydrophobic when small bits of soil become coated in organic waxy substances. Fungi and plants naturally release these substances into the soil. They basically “waterproof” the individual particles of soil. In healthy soils, microbial life breaks down these waxy compounds. But soil microbes eventually die out when the soil becomes too dry.

A slow, steady rain will eventually reverse this condition. The smell of rain – called “petrichor” – actually comes from soil bacteria that spring into life when exposed to moisture.

On the other hand, a hard and fast rain will likely run off before sufficiently moisturizing the soil, possibly carrying your rich topsoil with it.

Natural mulch like wood chips or leaves help to keep soils from becoming hydrophobic during times of drought. It reduces water evaporation. It also reduces compaction and crusting, which can lead to water running off instead of soaking in. In addition, mulch reduces soil temperature. But laying mulch on dry soil won’t alleviate the condition.

The weather forecast shows a good chance of rain this weekend, with possibly an inch or two of precipitation.

It might seem counterintuitive, but it’s a good idea to water before a rain during times of drought like this. This alleviates the hydrophobic conditions in the soil. If it does rain an inch or two, more of that rain will penetrate the soil instead of running off.