There is a sudden demand for more water as fruit enlargement occurs and if the extra soil moisture requirement is not met, then blossom end rot of the fruit can ruin the crop. On sandy soils light, supplemental fertilizer applications are needed for the first few weeks of the season. This is to help encourage the development of strong plants that can support heavy yields. Soils that have been heavily amended with organic materials can sometimes provide enough nutrients without supplemental fertilization. Knowing the right time to fertilize and when to cut back is one of the keys to heavy production.
Tomatoes have two growth stages vegetative and reproductive.
The goal should be to quickly grow a relatively large, healthy plant and then back off on the fertilizer as it reaches the reproductive, or fruiting stage. Much tomato production is missed because some gardeners continue to provide excessive fertilizer too late in the season. This practice often leads to a big bush or vine and low yields. Most major tomato diseases are caused by fungi, while a couple are caused by bacteria. Because these organisms are microscopic and early infection is not seen with the naked eye, control measures should begin before visual symptoms are present.