Like most other crops, tomatoes perform best in a good, rich garden soil. However, nitrogen fertilizer over two pounds per 1,000 square feet per year might be excessive. All fertilizer should be applied before planting to promote the development of sturdy plants to carry the fruit load later on. After the fruit sets, the emphasis should be on its maturing.
Occasionally, if heavy rains occur, soil nitrates may be depleted. Replenish them with another one pound of nitrogen per 1,000 square feet. This should not be done after August 1 because it will induce vine growth at the expense of ripening fruit.
For more information read: Fertilizing the Vegetable Garden
