It can be frustrating to carefully nurture your tomato plants, only to have the fruit fail to set. Blossom drop and failure to set fruit can be caused by extremes in temperatures, too much rain, or high humidity. While you can't control the weather, there are other things that you can do to increase fruit set and tomato production.
Transplant tomatoes when the weather has warmed. Night temperatures below 55 degrees F cause blossoms to fall off before pollination, according to the Washington State University Extension. Use tomato-set hormones to increase fruit set during cold weather.
Plant tomatoes in a sunny location. Tomatoes require eight to 10 hours of daily sunlight for optimum fruiting. Under artificial light, reduce lighting to stimulate fruit setting. According to the Virginia Cooperative Extension, tomatoes will not set under too much light.
Test the soil fertility. According to the Virginia Cooperative Extension, too little or too much fertilizer can reduce fruiting. Too much nitrogen fertilizer stimulates excessive vine growth, with little to no fruiting. Likewise, too little nutrition and moisture stunts growth. Apply fertilizer as recommended by the soil test.
Water regularly, but be consistent and avoid over watering. According to the Washington State Extension Service, too much water can cause blossoms to drop. Approximately 1 inch of water weekly is needed. A 3- to 4-inch layer of mulch applied when the weather warms will help conserve moisture.
Keep the plants cool. When daytime temperatures rise above 90 degrees F, flowers are reduced and tomatoes fail to set. Night temperatures above 70 degrees F also reduces fruiting, according to the Virginia Cooperative Extension Service. In hot climates, plant tomatoes early in the spring and again in the fall, avoiding the hottest part of the summer. During hot, dry weather, use a shade cloth and keep the soil moist.
Pollinate flowers by hand if insects are not present or when the humidity is high. Shake the stem vigorously every other day, or brush inside flowers with a cotton swab or small paintbrush. Mid-afternoon is the best time for hand pollination.