I have some potting soil that I'm using for a self watering planter. It's peat moss based, and I see some perlite in it.

I notice that it's wicking too much water (too wet). I tried the 2 knuckle test and can tell that it's just a little too must down there. I also tried a moister meter, and it shows that moisture is on the high side.

Is there any soil amendments that I can add in to reduce the amount of water this stuff will hold? My goal is to slowly add something to reduce the moisture retention, until I get it just right. But what can I add?


3 Answers 3


Actually sand will work for a short period of time. But then the compost will get compacted. The longer term solution is to add horticultural grit. This will add air porosity to your compost and water will drain well. You also need to make sure your pot has drainage holes to let the water out. Avoid the compost filling these holes as I moves when watered by placing crock just over them.

Grit can also be used as a top dressing to avoid splashing plant when watered and control weeds.

It would be useful to know what plants are going in. Different compost mix should be used depending on plant’s habits.


  • What exactly is horticultural grit? It is anything that's rocky/gritty? Will perlite or vermiculite work?
    – NL3294
    Commented Jun 11, 2018 at 23:42
  • I have added a picture. Small stones that allow air between soil particle. Plus they stay wet for a while and keep moisture... but not too much!
    – user33232
    Commented Jun 12, 2018 at 5:21

Something relatively easy to use to improve drainage is sand, also you could mix in some organic matter like compost to make the water drain a bit faster. Hope it helps.


How is the soil getting water? An alternative solution would be to reduce the amount of water going into the soil in this location.

Consider also the drainage from underneath. If you have great soil and put it in a pot that does not have drainage holes and then water it too much the water will site in the bottom. Similarly, beds built on top of hard-clay and filled with good soil can have drainage problems that cause the good soil to become too moist.

  • It's a 5 gallon self watering container, so it's getting water through capillary action from the water in the reservoir below.
    – NL3294
    Commented Jun 11, 2018 at 17:09
  • Ok, that definitely means my answer is not helpful to your situation :)
    – greggles
    Commented Jun 12, 2018 at 17:07

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