Hi, Grow mine the same as you--underlights in my basement in the winter and under a tree during the summer. I fertilize once every two weeks during spring and summer and then cut back to every two weeks in the winter. I also use super thrive with each watering. I grow mine cool in that my basement is unheated . Winter temps are 55 to 65 degrees. I have had great luck with them blooming for me. I only use bloom booster when i see a spike forming. Once the buds start to develope I stop the bloom booster. If you are having robust vegetative growth there is a chance that you may be feeding them too much. That could be a reason for them not blooming for you. I am far from an expert but have had good luck with my Oncidiums growing them as I have stated. Good Luck!