Tomatoes are the most popular plant in American backyard gardens, and it's easy to see why. In addition to being easy to grow, the taste of a home-grown tomato surpasses anything you get from the supermarket. Tomato plants thrive in warm sunny spots, and they also require plenty of water for optimum results, the University of Illinois Extension reports. Before planting your tomatoes, make sure you understand how and when to water them.
Because tomatoes mainly consist of matter -- 95 percent of the fruit is water -- they require plenty of water throughout the growing season, the University of Missouri Extension reports. The plants need between 1 inch and 2 inches of water weekly. Regular rain can meet these needs, but you'll need to supplement the water supply during dry spells.
Tomatoes do best when the soil is thoroughly soaked. During each watering, the water should reach a depth of 6 inches to 8 inches, the North Carolina Cooperative Extension advises. Instead of daily waterings when only the soil surface receives moisture, water the plants deeply once per week when rain is not forecast.
You can help your tomato plants conserve moisture by mulching around them so the soil is protected from the hot sun. You can use any organic matter for mulch, or place black plastic around the plants. If you use organic materials, wait until the soil has completely warmed up in late spring or early summer to spread the material, the University of Illinois Extension advises.
Tomatoes growing in containers have different watering needs than those planted in the earth. Because they have a smaller supply of soil, they benefit from more frequent waterings. The Missouri extension advises watering container-grown tomatoes daily if needed because of lack of rainfall.