Container-grown plants must be fertilized more often than plants growing in the ground. Because of the need for frequent watering, nutrients are constantly being leached out of the container's growing medium. Fertilize every two weeks with a general-purpose garden fertilizer, following directions on the label. To prevent burning the roots, water the plant well before applying the fertilizer.
It is particularly important with tomatoes that you check the top of the soil frequently to determine when it needs watering. Blossom-end rot is a common disease that can be caused by uneven moisture conditions.
For more detailed information on growing tomatoes in containers, read the University of New Hampshire publication: Growing Tomatoes.
