It partly depends on the height of the pots you use but I use 4" to 6" tall disposable cups to pot in and I have the water levels at about 1/2" in the trays they stand in. I find the plants like being top-watered about once a week and as long as they don't get dry it is o.k. to let the water level go down in the tray between refillings. A periodic top-flushing of the pots, say every 2 months or so, will help keep the soil 'sweet'. At least this has worked for me.