Mike,
The plants in the first photo are Xanthosoma sagittifolium.
I cut off leaves only after they have yellowed completely - the plant does reabsorb some nutrients back from dying leaves.
I don't induce blooming on my plants, instead preferring to rely on coincidental blooming to enable crosses. Over the years, I've learned the blooming cycles of various species so I have a good idea of when to try, and what to try it with. Also, I've learned natural ways to delay or speed up blooming so as to increase my chances of getting coincidental blooming. Cold or cool weather will delay blooming and also delay male/female anthesis.
I can get trunk in a year's growth but I push them to grow big enough to bloom. Big Ears are usually heavy feeders so inadequate fert availability can stunt them or hold them back. A plant on pace can put out nearly a leaf a week. If yours are slower, they may not be getting enough light, fert and/or water.
Top size relative to trunk is, again, dependent on adequate soil fertility. Low fert availability will lead to smaller top growth and slower growth overall. it is not sheer quantity, but consistent availability. Light feedings often are better than heavy feedings infrequently unless you are using a high quality time release mix with a known release time/effective duration.
The Big Ears will keep on going for years if maintained properly. If in pots, sometimes it means repotting with fresh soil and fert each year; if in the ground, you have to make sure they get enough fert and that the soil is well draining. The smaller "jewel" Alocasias can expire after a few years due to their finicky nature.
Hope this helps,
LariAnn
