Tomatoes grown in containers can actually be easier to grow than those grown in a conventional garden. There are some very simple guidelines that should be adhered to in order to ensure success.
Needless to say Good drainage holes should be in every pot you plant in. Pot Size: Size Matters - The more growing room the root system has, the better the roots will develop and the healthier and more productive the plant will be. A container can never be too big, but it can certainly be too small, leading to spindly "pot-bound" unhealthy and stifled plants.
Dwarf tomato varieties will work in smaller containers, I usually grow a few in five gallon buckets with holes drilled in the base for drainage. Standard size tomato plants - in 5 gallon buckets are not a good idea. They easily become top heavy, particularly on windy days.
Depending on the variety, tomato plants can grow 6 to 8 feet tall with a circumference of 2 feet or more. Smaller containers most definitely lead to smaller plants and less tomatoes.
Moisture for Potted Tomato Plants
In balmy summer weather pots heat up significantly quicker than ground soil, so keeping them well watered and mulched to retain moisture is a must.
Mulch on the soils surface, such as wood chips or decorative bark is not only aesthetically appealing inside or outside it is beneficial to the health of your tomato plants.
Trays under the pots are used for house plants to catch excessive water, they aren't necessary with tomato or other outdoor plants. The trays will hold too much moisture at the base of the roots, for too long and could not only lead to root rots, but can literally drown the plant.
When you give a baby a bath, you don't hold his head under water - don't do it to your tomato plant.
Soil, Fertilizer and Compost for Potted Tomatoes
Tomatoes respond well to fertilizer, but not excessive. Too much nitrogen fertilizer can result in plants with excessive vine growth but lowered fruit production.
Compost added to the containers is a good idea only if you intend to keep the plant outdoors. Indoors - well yes, it will still benefit the plant, but compost and other decaying organic matter is not something I normally bring into my home. Some people use worm castings, if you have access to these -go for it. See Worm Composting.
If at all possible try not to use soil from your yard, especially if you are going to bring your plants inside. Potting soil with some vermiculite and or perlite is best. If you are going to use ground soil - it will work - but potting soil is best.
Fertilizer in containers will wash out, where as in the ground - it is retained in the soil much longer. With container plants, smaller but consistent doses of soluble fertilizer with their watering is advisable. I also like to add a small amount of Epsom salts to the soil. Tomatoes frequently suffer magnesium deficiency relatively late in the season, which leads to lowered fruit yield when it is too late to correct. They will benefit from Epsom Salt applications not only when being planted, but at both ends of the plant life cycle as well as during the growing season. See - Epsom Salts as Fertilizer. Some Fish emulsion wouldn't hurt either.
Make Sure Your Plants Get adequate light. Tomatoes thrive in full sun, 6 - 8 hours daily. Even if your tomato plant is in a bright sunny location , portions of the plant are still sometimes deprived of sunlight if the plant is not lightly pruned and adequately supported. Tomato cages or Stakes and ties are a must, especially on larger plants.
If you grow them indoors, be sure to place them where they'll get the most sunlight, near a window or under a skylight. As they are mobile moving them from time to time to take advantage of the available light is a good idea.
For the purpose of Pollination, on tomato plants grown indoors, once the plants have flowered give them a little shake or put a fan on them from time to time to help the spread of pollen. Of course this isn't necessary on outdoor plants as Mother Nature will take care of that.
There are a number of plants that grow well with Tomatoes, and have a mutually beneficial relationship. In a pot however, with limited space and resources the only plants I mix in with the Tomatoes is a few small fine leaf chives, or sometimes garlic. Garlic releases sulfur into the soil that is beneficial to Tomatoes and detrimental to soil borne pathogens. Chives as well as garlic emit a pungent aroma which repels many insects. Garlic is not a good idea on inside plants as the smell can be over powering at times.