Most tomatoes do just fine in a 14-inch pot or larger. The keys to healthy potted tomatoes are consistently moist soil and regular feedings. Consistent soil moisture helps eliminate plant stress and prevent disease. Plants in pots tend to use up all the available nutrients in the pot, and tomatoes can be heavy feeders. If you use a liquid plant food, dilute it slightly and use it at least every other time you water. As with tomatoes grown in the garden, containerized plants should have full sun (6-8 hours per day).