Blossom drop is a common tomato growing problem that can be extremely frustrating to the home gardener. Otherwise healthy looking tomato plants set flower blossoms, only to have them dry up and fall off the plant before a fruit is formed.
What Causes Blossom Drop in Tomatoes?
Blossom drop can be attributed to several causes, most often related to either temperature and / or stress, which makes it very hard for gardeners to control.
Here's a sampling of things that can go wrong.
- Temperature Too High or Too Low
- Lack of Pollination
- Nitrogen - Too Much or Too Little
- Humidity Too High or Low Humidity.
- Lack of water
- Stress from insect damage or disease
- Too Heavy Fruit Set
The most frequent cause of tomato blossom drop is temperature.
- High daytime temperatures (above 85 F/29 C)
- High Nighttime Temperatures (above 70/21 C)
- Low Nighttime Temperatures (below 55/13 C)
Tomatoes grow best if daytime temperatures range between 70 F/21 C and 85 F/29 C. While tomato 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 NV, "...temperatures over 104 F / 40 C for only four hours can cause the flowers to abort."
Controlling Tomato Blossom Drop
- 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 F/13 C 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. (Early Girl, Legend, Matina, Oregon Spring, Polar Baby, Silvery Fir Tree)
Select heat 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. (Florasette, Heat Wave, Solar Set, Sunchaser, Sunmaster, Sunpride, 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. You should attract more bees if you 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 40-70%. If humidity is either too high or too low, it interferes with the release of pollen and with pollen's ability to stick to the stigma. So pollination will not occur.
If humidity is too low, hose the foliage during the day. This will both cool the plant and raise the humidity. 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. (Eva Purple Ball, Flora-Dade, Grosse Lisse, Jubilee, Moneymaker, Sun Gold, Taxi, Yellow Pear)
- Water Deeply, Once a Week, During Dry Weather. Tomatoes have very deep roots, sometimes going down into the soil up to 5 feet. 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.
Nothing will guarantee fruit set. Things 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, then you should consider the cultural causes of tomato blossom drop. Choosing a suitable variety and keeping your plants healthy will give you an edge.