these plant's done very well every year until this year. Do I need to thin them or just feed them?
What to do?
I feed all mine every week.
But those are invasive here and we try not to plat them. The plain green Colocasia escuelenta, as well as the Xanthosoma saggitifolia, are both on the FL list of "please don't plant these anymore" I am fairly certain. Once they get loose its all over. You will get more and more as the years pass til they overgrow your space so you will eventually have to thin them, it just takes longer in cooler places than it does here, where it generally happens after one wet simmer.
They're native to this area and spread by sending out runners, sometimes quite long. They normally live in water so usually you don't get a "salt" build up as you can in a garden/dry land situation. Flushing from rains washes excess salts away. In gardens you can end up with some essential minerals depleted and non-essential ones building up. There are cultivars that don't have runners and spread more slowly.