Flowers but No Tomatoes

Tomato plants that won’t set fruit is a common problem often caused by Mother Nature. But there are things you can do to help.

Tomato Blossom Drop by Midwest Gardening.jpg

There are a number of weather conditions that can cause your tomato plant to stop producing fruit or never even start. Once you understand the potential causes you may be able to prevent the problem in the first place or help the plant to start making fruit.

Pollination

You may not be aware that tomatoes are self fertilizing. The tomato flower has both male and female parts so the pollen simply has to drop from the stamen down to the stigma. However pollinators such as bumblebees vibrating their wings in the blossoms can encourage the process so make sure you are encouraging pollinators in your gardens. There are still a number of things that can happen to prevent pollination.

  • Growing tomatoes in a greenhouse or tunnels can not only prevent access to pollinators but also inhibit the airflow that will cause the blossoms to drop pollen. Make sure your plants are exposed to the breezes. Gardeners growing in protected environments will often “shake” the plant to dislodge the pollen. Vibration of pollinator wings can be mimicked by snapping string line supports, causing a shudder through the plants.

  • Tomatoes do like some heat, but consistent heat above 75 degrees at night as well as over 86 degrees during the day can render the pollen sterile. Keep the plants well watered and healthy so that production can begin again when the weather improves.

  • Humidity levels can complicate pollination in two ways. In high humidity the pollen may be sticky enough not to be able to drop. In low humidity it drops readily but may not stick to the stigma. Ideal humidity range is 40 to 70 percent. To combat high humidity effects encourage pollinators to do the work by planting pollinator attracting insects in the garden. In low humidity, lightly misting the plants may help

Temperature

Extreme heat and cold will cause a tomato plant to work solely on survival and give up fruit production. Tomatoes set fruit when day temperatures are about 70 to 85 degrees.

  • As noted above, pollen may become un-viable. New blossoms produced after the heat subsides will begin to produce again. If you are growing in hot zones also be sure to select heat tolerant varieties.

  • Most tomatoes will not set fruit if nights are consistently below 55 degrees. It is hard not to get anxious to plant, but do not plant tomatoes early. In cool Northern regions select varieties tolerant of cold nights.

Nutrition

Ideally tomatoes should be grown in fertile soil. But tomatoes are very heavy feeders and even rich soil will not keep up with what the plant needs to produce fruit. Proper water is just as important. These good practices will keep your tomatoes properly fed and watered:

  • Use a fertilizer high in potassium, which promotes flowering. Formulations specifically for tomatoes are ideal, organic is even better.

  • Fertilize every 3 to 4 weeks.

  • Provide at least one inch and up to three inches of water per week. Do not water daily. To deeply soak the soil water only once or twice per week. Tomato plants develop very deep roots to take in adequate water and nutrition, and without moisture deep in the soil that won’t happen.

Other Mother Nature Problems

  • Referred to as Blossom drop, the problem is not a disease. It is an unfortunate but common problem brought on by lack of pollination or stress, usually from the conditions noted above. Perfectly healthy plants form blossoms but no fruit develops. Eventually the plant abandons and drops the blossom.

  • Unusual heat or cold also inhibits insect activity. The pollination process that may already be having difficulty in those conditions receives no assistance from pollinators.

  • Occasionally a very healthy tomato plant growing in ideal conditions will develop an enormous number of blossoms. They will compete for water and nutrition so not all will survive. In this case some blossoms will fail to set fruit but there will be plenty that do. Some gardeners will pinch of blooms when this happens but it is best to let the plant decide which are weakest and drop them.

Sharon DwyerComment