How to fertilize flowering tomato plants?

No crop typifies summer more than red, ripe garden tomatoes. Their natural coloring, rich smell and compact juiciness contrast remarkably with tomatoes sold in grocery stores in midwinter. Tomato plants need nitrogen and phosphorus, but not to excess. A healthy layer of composted manure over the planting bed -- 10 pounds per 10 square feet -- mixed into the top 6 inches of soil, will take care of the tomato plants through flowering. It doesn't pay to offer more, since excess nitrogen produces tall, lush stems but reduces the crop. However, when your tomato blossoms open, it is time to fertilize again.

1. Inspect your tomato plants every day after buds begin to develop. When the majority of the blossoms are open, the tomatoes are starting to set their fruit.
2. Sidedress tomato plants with nitrogen-heavy fertilizer at fruit set. Dig shallow grooves in the soil on either side of each tomato plant. Put the proper amount of fertilizer in the grooves, following the label directions. Apply water to the grooves very slowly and thoroughly to transfer the fertilizer to the plant's roots.
3. Repeat the sidedressing every four or six weeks during tomato season. Take care not to use too much fertilize, as you do not want excess nitrogen to wash out of the root area and contaminate ground water.