Anemic sunflower plants? I have planted sunflowers in flower boxes around my deck. They've...

I have planted sunflowers in flower boxes around my deck. They've come up to just about 3feet in height and are starting to win dead brown leaves on the lowest part of the stem. The leaves on the rest of the stem are a wispy green and I was wondering if this is normal.
Answers:    pinch bad the lower leaves, water well and make the addition of a little fertilizer.
Good luck!!
try a high nitrogen fertilizer