I think sweet potatoes take around 90 days -- but they need a lot more heat than the "Irish" potatoes do (I've tried sweet potatoes before and the best I've ever done is a few very small tubers; but Irish potatoes grow fine here and a lot are grown commercially in my area. From what I've read, you can start digging "new" potatoes when the plants start to flower (although some of mine never do so, making that a little tricky), and dig mature potatoes when the vines shrivel. Basically, here in the north I can plant (usually) in May, and the plants die down by early September.
Could it be that it's just too hot in Texas now?
