Blossom Drop in Peppers and Tomatoes

Tomato and pepper petals normally dry and fall once the tiny green ovary behind them starts to swell. That is fruit set. With blossom drop, the entire flower browns or dries up and falls away without an enlarging fruit. On a tomato, look at the small joint in the flower stem. An aborted blossom often yellows at that joint and snaps cleanly away there, while a set fruit keeps the joint attached behind the swelling ovary.

Tomatoes are self-pollinating, and peppers are mostly self-pollinating. Tomato pollen sits inside a cone of anthers and releases when the flower is moved. A bumblebee can do that work, as can a light tap on a tomato support during a mild morning. Pepper flowers have a different structure, and wind or insects can move their pollen outdoors. Look at several fresh flower clusters before deciding the plant has stopped producing.

A single hot afternoon is not always enough to stop fruit set. Several hot days followed by warm nights are harder on flowers. University of Minnesota Extension flags sustained tomato weather above about 85°F by day and 70°F at night as a common blossom-drop pattern. Peppers often lose flowers once daytime temperatures move above 90°F.

Heat can leave tomato pollen less viable or prevent pollen from growing the tube needed to fertilize the ovary. A blossom-set spray is a synthetic hormone product that tries to make the ovary swell without normal fertilization. It can help with low-temperature flower drop, but it does not rescue flowers in high heat and may produce misshapen fruit.

Treat these temperatures as general thresholds. Humidity and the length of the hot spell both affect how much fruit set is lost.

Humidity matters too. Tomato pollen works best in a middle range. In very dry air it may not stick well to the stigma. In humid, still air it may not shed from the anther cone. This is one reason a humid summer garden and a hot, dry one can show the same dropped flowers for different immediate reasons.

Heat is tougher on a plant whose soil has dried hard, then been flooded with a catch-up watering. Before the afternoon sun is strongest, lift the mulch and feel the soil below the surface near the plant. If it is dry where the feeder roots are working, water slowly enough for it to soak in rather than running down the path.

Mulch helps by slowing evaporation from the soil surface. A light layer of clean straw works well around established tomatoes and peppers, kept back from the stems. In a container, check more often because the root zone can dry far faster than a garden bed.

Dark plastic containers can hold enough heat to damage roots even when the mix is still wet. Use a light-colored pot where you can, or shade the sunward side of a dark pot during a heat wave.

Extra nitrogen can make a tomato or pepper look impressive while it puts energy into more leaves and shoots instead of fruit. Dark green foliage and strong growth with few set fruits is a good reason to stop adding high-nitrogen fertilizer for now.

Fertilizer does not bring back dropped flowers. If a plant is pale or stunted as well as losing flowers, that is a separate problem worth checking before the next feeding. Do not switch automatically to a high-potassium bloom formula. Potassium should not be assumed deficient, and a soil test is a better basis for a recurring fertility question.

For a string of very hot days, a 30 percent shade cloth held above the crop can take the edge off the afternoon sun without turning the bed dim. Leave the sides open so air can move through.

Take off a fabric or plastic row cover once tomatoes and peppers begin flowering. These covers can add heat and reduce air movement around flowers. They are useful protection for young transplants, but they are not a summer cover for a flowering plant.

Indeterminate tomatoes and peppers keep making flowers through the season. Once nights cool and the root zone is steadier, later blooms may set fruit normally even though the first cluster fell. Give the plant time to show you what the next cluster does.

Determinate tomatoes set much of their fruit in a shorter window. A hot spell during that period can reduce the season's total harvest because there may be fewer later flower clusters to replace the lost ones.

If heat is a regular summer problem, try a heat-tolerant variety next season. Cherry tomatoes often set over a wider temperature range than large-fruited slicers. 'Solar Fire' and 'Phoenix' are heat-set slicers worth trialing when a concentrated harvest suits your plans.