Fixing Water Repellent Soils

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Water Repellent Soil

One of the most prevalent myths Don encounters is ‘Why is my plant sick when I water it well?’

The potting mix could be the problem, as it could be water repellent. Don conducted an experiment using a mignonette lettuce, putting it in standard potting mix and watering it very well, in fact he filled the pot with water and watched it drain right through. You’d think with all that water passing through, the potting mix would be wet.

Don took the lettuce out of the pot and the entire potting mix was dust dry, the water didn’t wet the mix at all. One of the problems is that modern potting mixes are 100% organic matter and as they age they actually become water repelling. When Don watered the lettuce, the water actually went down the sides of the pot not even getting near the plant’s roots.

If you have this problem, not only with your pots but also with your soil, you need to use a wetting agent, there’s lots on the market to choose from and they work for up to six months. Don then treated the lettuce with Super Soil Wetter, following the instructions on the pack pouring the solution over the lettuce again and watching the water drain out the bottom of the pot again. This time when Don pulled up the lettuce, the potting mix was wet.

So adding a wetting agent to a potting mix is often essential. Wetting agents are just a very gentle detergent, much the same as if you get a duck and put it in detergent filled water, the duck would sink (do not try this at home). If you’ve got a potting mix which is water repelling and you add a horticultural wetting agent to it, the surface tension breaks down and the potting mix absorbs the water and the plant grows well. You will need to reapply the wetting agent every six months.

By the way, old potting mixes can be thrown straight into the garden as it’s a reasonably good soil conditioner. 

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