Lower leaves yellowing on Alabama Crimson Honeysuckle?

I planted 3 Alabama Crimson in containers (1.2 cu ft each) this spring and they have grown like crazy, covering over 3 trelllis already. All of a sudden I'm getting yellow leaves on the bottoms of each plant. The yellowing starts on the outside of the leaves and works its way in. Rusty looking spot start when the yellow ring is in from the edge of the leaves about 3/4 of an inch.

Don't worry about it because these are new plants? Fertilize them? Or what? Any idea what may be causing this? Thanks -- Ed

sounds like nitrogen deficiency or potassium deficiency... you might want a second opinion but i'd try lightly fertilizing them with a fish emulsion mix.