I've been having problems with my sunflowers not reaching thier full height. Last year I planted a row of Mammoth sunflowers. The packet said they'd get about ten feet tall. The tallest one was about two feet. They flowered way too soon. Well I planted again this year and moved them to another area. I've planted varieties from Burpee this time: Kong, American Giant, Sunforest and mammoth. Some are supposed to be 15 feet tall and I had these dreams of walking through many many massive sunflowers. Well the tallest one is four feet and is already getting a flower head. OH NO!! What's wrong? Why won't they get their full height? It's really annoying. Even the black oil sunflowers the birds plant on accident by dropping them have only gotten to about nine inches. Help!