hello,i have a 2' tall angelwing type begonia.the leaves from about 1' tall and taller are great,however below they are getting sparse and some have fallen off.how do i prune this plant/will i have to sacrifice the lushness at the top?do i have to take cuttings and start over?its taken a few years to get this tall, i am hoping to keep it tall and lush,any ideas?thanks alot