Why do you think you need Iron ?

Plants main food is N,P,K.. so all fertilisers are graded by this ratio, eg. 8:2:2 [high N for growth] or  1:3:10 [for flower/fruiting]

Most people kill pot plants by overwatering, rotting the roots, overfeeding is also very common and easy to do.

Nitrogen deficiency, if you have it, is usually shown as a yellowing, from the bottom of the plant.