Tomatoes are warm-season vegetables, producing an abundant crop from mid-summer until the first frost of fall. Tomatoes require regular irrigation to keep the soil moist, especially during the heat of summer when the plants are producing the most fruit. If the soil is allowed to dry out, the plant suffers and may not recover fully from the drought stress. Keeping the soil moist does not necessarily require frequent watering if proper preparation is taken to ensure the soil's moisture retaining ability.
Lay a 2- to 4-inch layer of compost over the soil prior to planting the tomatoes. Work this into the top 6 to 8 inches of the soil with a power tiller or hoe. The compost adds organic matter to the soil, which helps retain moisture without becoming soggy.
Water the tomatoes once weekly. Water at the base of the plants so that the moisture permeates the soil instead of evaporating off the foliage. Water until the soil feels moist to at least a 6-inch depth when you stick your fingers into it. Weekly, deep watering encourages the tomatoes to form deep roots, enabling them to find the deep soil moisture when hot weather dries the soil surface.
Cover the bed with landscape fabric when the soil begins to warm, usually within four weeks of planting the tomatoes out to the garden. Lay the fabric around the plants, but do not allow it to come in direct contact with the stems. Landscape fabric preserves soil moisture and also prevents the tomato plant from contracting fungal diseases from the soil.
Lay a 2-inch layer of organic mulch, such as grass clippings, straw or bark, over the top of the landscaping fabric. Use a 4-inch layer of partially decomposed compost if you are not using landscape fabric. The insulated soil remains moist as the water evaporates much more slowly.