Blossom drop is a common tomato growing problem that can be extremely frustrating to the home gardener. Healthy-looking tomato plants set flower blossoms, but they just dry up and fall off the plant before a fruit is formed. There can be many causes of blossom drop, but the most common is excessively high or low temperatures.
Cause of Tomato Blossom Drop
Many of the problems that cause blossom drop can be difficult to control because they are related to temperature and plant stress, including:
- Temperatures that are too high or too low
- Lack of pollination
- Too much or too little nitrogen
- Humidity that's too high or too low
- Lack of water
- Stress from insect damage or disease
- Excessively heavy fruit
The most common cause of tomato blossom drop is temperature. Tomato plants can get stressed if the high daytime temperature is above 85 degrees Fahrenheit, the high nighttime temperature is above 70 degrees, or if the low nighttime temperature is below 55 degrees.
Tomatoes grow best if daytime temperatures range between 70 and 85 degrees Fahrenheit. While the plants can tolerate more extreme temperatures for short periods, several days or nights with temps outside the ideal range will cause the plant to abort fruit set and focus on survival. According to the University of Nevada Cooperative Extension, temperatures over 104 degrees sustained for four hours can cause tomato flowers to abort.
Controlling Tomato Blossom Drop
Nothing will guarantee fruit set. Because factors like temperature and humidity are out of the gardener's control, sometimes you just have to be patient and wait for conditions to correct themselves. If the weather seems fine and other gardeners in your area are not having fruit set problems, consider the cultural causes of tomato blossom drop. Choosing a suitable variety and keeping your plants healthy will give you an edge:
- Grow varieties suited to your climate: Gardeners in cooler climates should not rush to get their tomatoes planted in the spring. Wait until nighttime temperatures are reliably above 55 degrees Fahrenheit, or protect them with a cover at night. You won't gain any advantage by setting them out too early. Choose early-maturing tomato varieties for spring growing in cooler climates, such as 'Early Girl,' 'Legend,' 'Matina,' 'Oregon Spring,' 'Polar Baby,' and 'Silvery Fir Tree.' Conversely, select a heat-tolerant ("heat set") tomato variety for areas with long periods of hot or humid weather. High nighttime temps are even worse than high daytime temperatures because the tomato plant never gets to rest. Heat-tolerant varieties include 'Florasette', 'Heat Wave', 'Solar Set', 'Sunchaser', 'Sunmaster', 'Sunpride', and 'Surfire'.
- Ensure pollination: Tomatoes need some help to pollinate. Either insects, wind, or hand-shaking of the flowers is necessary to carry the pollen from the anthers to the stigma. During weather extremes, there are often no insect pollinators in the garden. One way to attract more bees is to plant nectar-rich flowers in your vegetable garden.
- Go easy on the fertilizer: Don't automatically feed your tomato plants every week. Make sure your soil is healthy, with adequate organic matter. Apply a balanced fertilizer at planting and again when the tomatoes start forming. Too much nitrogen encourages the plant to grow more foliage, not more fruit.
- Work around the humidity: The ideal humidity range is between 40% and 70%. If humidity is either too high or too low, it interferes with the release of pollen, as well as with pollen's ability to stick to the stigma so that pollination does not occur. If humidity is too low, hose the foliage during the day to cool the plant and raise the humidity. However, this is not recommended in areas with high humidity or when fungus diseases are present. Gardeners in high-humidity areas should look for tomato varieties that aren't bothered by humidity, such as 'Eva Purple Ball', 'Flora-Dade', 'Grosse Lisse', 'Jubilee', 'Moneymaker', 'Sun Gold', 'Taxi', and 'Yellow Pear'.
- Water deeply, once a week, during dry weather: Tomatoes have very deep roots, sometimes going down 5 feet into the soil. Shallow watering will stress and weaken the plants.
- Keep your tomato plants healthy: Use good cultural practices and treat for disease as soon as symptoms appear.
- Sometimes the problem is just too much of a good thing: When a tomato plant has too many blossoms, the resulting fruits are all competing for the limited food supplied by the plant. Only the strong will survive. The plant will automatically abort some flowers, much like June Drop of tree fruits. Once the initial crop is harvested, the problem should subside.