Reply To: Is 2 inch of pebles from the bottom OK? July 25, 2019 at 3:28 am #205 JoshKeymaster Only 1 inch / 25mm max ….. too high and the water will not wick up ….. you’ll get away with 2 inches if you top water until the roots are down at the bottom. This reply was modified 5 years, 1 month ago by Josh.