In the Daylily list, Susan Bergeron of Canada reported on an experiment she did testing usefulness of coarse drainage materials in a pot. These are her words below, slightly rearranged to correct a typo she tells me she made: _________________________ Last week we discussed the suggestion that drainage material in the bottom of plant pots doesn't help, and may actually impede, drainage of the medium above it. The issue was raised by Dr. Gillman at the MWS [Midwinter Daylily Symposium], and this is also what I was taught when I took soil science, so I said that I believed him to be correct. I tried to do an experiment to confirm it for anyone still skeptical, which actually didn't prove it! I said I'd try again when I had the materials to do it properly, and I also realized the way I'd done it the first time was somewhat flawed. For anyone interested in the methodology of attempt 2, keep reading. For anyone interested only in the result, skip to the end of this email. I took some clear, plant pot shaped, containers which also had measurements on them at 1, 2 and 3 cups. I made drainage holes in the bottom. I filled Container 1 to the top with Miracle Gro potting mix only. I firmed the mix until the level was the same in both containers, i.e. to the 3 cup level. I then filled Container 2 to the one cup level with non-absorbent polystyrene packing material as drainage, then topped it up to the top with Miracle Gro potting mix. (This is what I realized I should have done in the first attempt because the media would be firmed around a plant being planted, and would also have compacted around a plant that had been in the pot for some time). So, we now have two containers, one full of potting mix to the 3 cup level, and one with one cup of drainage material and two cups of potting mix. I placed each container over a plastic container to catch the drainage water individually. Then I placed a coffee filter over each container so that the water was distributed evenly and didn't disturb the medium (another omission I made the first time). I then poured 440 ml of water into each container. When they had finished draining in an hour, I measured the amount of water that had drained out of each container. 85 ml had drained from Container 1 (three cups of potting mix), and 160 ml had drained from Container 2 (two cups of potting mix over one cup of coarse drainage material). I deducted these amounts from the original 440 ml and was left with: Container 1: 440 - 85 = 355 ml still in the container Container 2: 440 - 160 = 280 ml still in the container Since there were three cups of potting mix in Container 1, 355ml divided by 3 equals 118ml retained water per cup. Container 2 (the one with drainage) contained two cups of potting mix, therefore 280ml divided by 2 equals 140ml retained water per cup. Therefore the container with the coarse drainage material at the bottom retained more water per unit volume of potting mix than did the container without coarse material at the bottom. Thus, according to this experiment, Dr. Gillman (and my soil science teacher!) would appear to be correct that drainage material in the bottom of a plant pot does not help drainage and can actually increase the amount of water held by each cup of potting mix. Just to make sure, I tried this again slightly differently, with one container having two cups of potting mix, and one having two cups of potting mix over a cup of drainage material, i.e. exactly the same amount of potting mix per container. I didn't wait an hour this time but measured the drained water as soon as it had more or less slowed down to an occasional drip. The result was the same. The potting mix alone retained 105 ml of water per cup and the container with drainage material retained 135 ml of water per cup of potting mix. Therefore, in these two experiments, coarse "drainage" material in the bottom of the pot resulted in the potting mix above it staying wetter per cup of medium than in a container of potting mix alone. Now to go clean up the kitchen...............! Sue Bergeron Ontario, Canada _________________________ You really have to read the above carefully. Susan did a careful experiment, and demonstrated to us what many experts have told us: Adding rocks, pottery chips, or polystyrene foam "peanuts" will not improve the drainage around the roots of a potted plant. Just thought folks might find this interesting. Jim Shields in chilly, foggy central Indiana (USA), where there is still snow on the ground after two days of mild weather P.S. Reproduced with Susan's permission PPS. 440 ml is probably just a little less than 2 cups. A liquid ounce is around 30 ml. ************************************************* Jim Shields USDA Zone 5 Shields Gardens, Ltd. P.O. Box 92 WWW: http://www.shieldsgardens.com/ Westfield, Indiana 46074, USA Tel. ++1-317-867-3344 or toll-free 1-866-449-3344 in USA