to NGA
Check to see how wet the potting soil is and how long it stays wet. Weirdly enough, putting gravel in the bottom of a pot does not increase drainage, but has the opposite affect. It could be that by trying to improve drainage, you have water logged the soil.
If you feel that the potting soil you are using will not drain fast enough, mix gravel, perlite or something similar into the soil, don't put it under the soil.
