Drainage issue in a really large pot
I have a 5 year old Shishigashira (lions head) in a really large ceramic pot. The pot is 3.5 feet wide, 3.5 tall. I fear that the one small hole at the bottom is not enough drainage. Short of taking the tree out of the pot in the heat of summer, is there anything I can do to improve drainage? The soil mix I used was 50% bagged top soil, 40% black cow brand manure, and less than 10% Miracle Grow Moisture control potting soil. Any suggestions? Thanks!