Two of the key components of healthy tomato plants are constant moisture and lots of sun. Sometimes it's hard to have one with the other since the sun dries up the water. Fortunately, you can use several techniques to help keep your potted tomato plants moist, so you can enjoy a plentiful harvest.
Mulch around your tomato plants. Use several inches of mulch, such as bark or pine needles. A layer of mulch will help the soil retain water by keeping it cooler and out of the sun so the soil does not dry up quickly.
Weed around your tomato plants. While weeds are rare in potted plants some can still sneak in, usually thanks to the wind, on occasion. Weeds only use up moisture and nutrients that you want your tomato plants to have, not the weeds.
Water in the early mornings and water slowly around the base of your plant. You can also water your tomato plants at night, but it is generally still hot at night. Around 6:00 a.m. is usually the coolest part of the day and by watering around that time, the water will have more of a chance to seep in past the mulch into the soil before the heat comes again and evaporates it.
Set the potted tomato plant in a tray or larger container of water. The pot you are using should have holes on the bottom for water drainage. It also can be used to water your plants from the bottom up. By keeping your tomato plants in water, the soil will stay moist. Replace the water when it dries.
Choose a light colored pot instead of a dark-colored pot. Dark colors absorb more sunlight, and therefore heat.
Make a watering wick or purchase a commercial watering wick. Use a plastic bottle, about 1 liter in size. Fill it with water, flip it over with your finger over the top and quickly bury it several inches into your soil (cap off). Refill as necessary.