Once in the ground, a deep watering every three or four days is better than a daily, light sprinkling. Keep the leaves and fruit off the ground in the interest of disease control. The easiest way to do this is to mulch under young plants with straw or hay. Thereaafter, be a lazy gardener with respect to tomatoes, and do not prune them. The excess foliage shades the plant, which increases fruit set and reduces splitting from the heat.
Nematodes can be a problem in old garden soils.
These tiny, wormlike creatures invade vegetable plant roots and cause them to swell and become distorted. This prevents plants from getting the needed nutrients, and yields go down. There is no chemical treatment for the home gardener. The best solution is to leave the garden soil vacant for a year and then add a lot of organic matter before reusing. Some varieties of tomatoes, designated by the letters V.F.N. after their name, are resistant to verticillium wilt, fusarium wilt and nematodes.