Growing plants from direct-seeding (seeding in the ground) is a bit trickier than it sounds. Normally, seeds planted in early spring will germinate without additional water. Later plantings mean the seeds have to be soaked before planting or the ground needs to be moistened before the seeds are placed. Once they have sprouted above ground, a daily light sprinkling will keep them growing. However, our recent very hot days mean that you may have to sprinkle the ground twice or more daily. Sprinkle so that the water reaches the planting depth and a bit below. Once the plant is actively growing, supply 1 inch per week in order for the plant to develop deep roots.. You do not want to waterlog or flood the garden. You can usually assess the water level in the ground by sticking your finger in the end of a row and feeling the moisture there. If you feel powdery,dry soil, you are not watering enough. Shade cloth placed above new seedlings will help keep them from burning in the sun. You can also use lightweight "floating row cover", a non-woven thin material that allows light and water to penetrate, but provides protection from direct sun.
Young tomato plants need consistent moisture, but not flooding or water logged soil. The use of wet/dry cycles (i.e. watering only when the soil is crusty and dry) is a good way to bring about blossom end rot in the crop. Consistent, even moisture can be supplied by soaker hose, drip irrigation or patient hand watering once every other day (depending on your soil--clay holds water longer; lighter soils need more frequent water). Plants should not be allowed to wilt, but if they wilt despite your careful watering, do not give them more water--the problem is likely that the roots are already waterlogged and the plant is struggling to "breathe".. .