My Mandevilla plant has beautiful and plentiful red blooms. Suddenly I find lots of green leaf drop, not yellow. Plant is in sunny area and is in an outside planter with the bottom cover that snaps in. This prevents dirt from flowing through the plant when it rains or is watered. Could the water in the base be harmful to its roots. Container is too big for me to empty after rain showers or watering. Should I remove the base which holds sitting water?