Why Do Flowers Fall Off Tomato Plants?

Environmental Causes of Blossom Drop

• Environmental circumstances can cause tomato flowers to fall off of the plant. Temperature plays a key role in helping your tomato plants to set fruit. If it is consistently too hot or too cold, the flowers will fail to set fruit or fall off of the tomato vine. Night temperatures that are consistently below 55 degrees F or above 75 degrees F harm the tomato flowers. Daytime temperatures in excess of 90 degrees F also affect fruit set on tomato plants. Excessive humidity can make it difficult for pollen to release properly and adhere to the flower's stigma, hindering the fertilization of the flower. High winds can also pull the flowers off of the plants.

Pest-related Causes of Blossom Drop

• Plants that are stressed by insect problems, frequently caused by aphids and thrips, can lose their flowers. Aphids suck the sap from tomato plants and leave a sticky residue on the tomato plant. Thrips carry the virus that is responsible for spotted wilt in tomato plants. Plants that have been damaged by one or both of these insects have trouble keeping the flowers intact.

Nutritional Causes of Blossom Drop

• Nitrogen is the most important nutrient associated with blossom drop problems. An inadequate supply of nitrogen can cause blossom drop, but so can excessive levels. Commercial fertilizers that are not specifically designed for use on tomato plants tend to have too much nitrogen for tomato plants. It can be easy to oversupply your soil with nitrogen, especially if you fertilize your tomato plants weekly to support them during the part of the season when you anticipate the plant will produce the majority of its fruit.

Treatment and Prevention of Blossom Drop

• You can't control the temperature outside, but there are some things you can do to help your tomatoes. Use a ground-covering mulch to help warm the soil and store heat when temperatures are cooler and provide some shade to relieve plants of hot daytime temperatures. If you know that summer temperatures soar in your part of the country, choose a heat-resistant tomato variety that can withstand the higher temperatures. Pests can be treated with insecticides; aphids can be washed off of affected tomato plants. Use a fertilizer formulated for tomatoes, and follow the manufacturer's instructions when applying it.