abscised flowers
abscised flowers

Blossom Drop of Tomato

Blossom drop is the loss of flowers. This is usually preceded by the yellowing of the pedicel. Flowers may either fall off or, as with jointless varieties, whither and die. Tomato plants lose their blossoms for several different reasons usually related to some kind of stress. The stress may be either nutritional, enviromental or some combination of the two. However, anything which would interfer with the pollination-fertilization process may result in flower loss.

Potential Causes
Nutritional causes:
Nitrogen plays a key role in blossom drop. Too much or too little nitrogen will result in the loss of flowers. I've received many letters from people asking about blossom drop and I usually find they are over-fertilizing. Unless one has sandy soils or they are trying to produce record breaking fruit, I see no need to fertilize every week (especially with the "blue stuff").

Enviromental causes:
Temperature - Excessive temperatures (low or high) will produce blossom drop by intefering with the pollination or fertilization process. Generally, day temperatures above 90F or night temperatures greater than 70-75F will interfer with fruit set resulting in the loss of flowers. Research has indicated that higher night temperatures have more of an influence.
High Humidity - can effect either the release of pollen from the anthers or the adherence of the pollen grains to the stigma.

Other potential sources of blossom drop:
Excessive wind
Stress related to insect damage - (usually thrips or aphids)
Stress related to foliar disease
Lack of adequete light
Extended light exposures - (24 hour exposure to a light source)
Excessive pruning

To prevent blossom drop from occuring always ensure proper nutrition and follow good cultural practices which reduce potential stresses such as foliar diseases or insect problems. Generally a well balanced fertlizer mixed into the soil before planting and a follow-up applictaion just after fruit set is all the nitrogen needed under most conditions. You can get around the heat issue by choosing heat tolerant cultivars or, as in some cases, overhead watering can help (note - overhead watering may not always be a good idea as it can encourage many foliar diseases).

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