As someone who regularly grows heirloom tomatoes, I have found it best to mix in some bone meal when planting tomatoes as it provides magnesium and calcium for the young plant. This mitigates the chance for blossom end rot. About two weeks after planting, I snake a drip hose through my bed, tack it to the soil with lawn pins and then cover everything with straw. The straw significantly reduces the splashing of rain and soil onto the lower parts of the plant and reduces the chance for fungus.