Fertilizing container plants

If the bottom leaves of the vegetables and flowers in your containers are turning yellow or light green this is most often due to a deficiency of nitrogen. This is more of a problem in containers due to the flushing of nitrogen out of the soil when watering. This is also more of a problem in raised beds than in regular gardens.
Nitrogen, unlike iron, is mobile within the plant. As new leaves are formed, nitrogen will be pulled from the lower leaves to the new leaves. Thus the lower leaves lose their green color resulting in chlorotic leaves.

Chlorotic leaves on tomato, pepper, eggplant and other members of the potato family (Solanaceous plants) are more susceptible to early blight caused by the fungus Alternaria solani. Applying fertilizer containing nitrogen on a regular basis during the growing season will help prevent chlorosis as well as early blight.

It is critical that you avoid excess applications of nitrogen as this results in more vines and less flowers and fruit. Any liquid fertilizer containing nitrogen will work to correct chlorosis. Instead of fertilizing at full strength, apply the fertilizer at half rate but twice as often as recommended. I do not suggest the use of fertilizer spikes in containers. Always make sure the soil is moist before applying the fertilizer.