Each summer, we never can wait to pick that first tomato from the vine.

But every year many unhappy gardeners are plagued with blossom end rot.

Blossom end rot usually appears as a brownish, water-soaked spot which gradually increases in size and turns black and leathery. It usually occurs early in the season and seems to improve as the season progresses.

Blossom end rot is not a disease, but a physiological disorder caused by not enough calcium reaching the blossom end of the fruit. As a result, the cells in this area die. Blossom end rot is worse after dry spells because the plant may not have sufficient water to move the calcium to the plant cells.

To control, be sure there is sufficient calcium in the garden soil before planting tomatoes. A soil test can tell you if calcium levels are sufficient. Gardeners who lime their soil on a regular basis are usually not as affected by this condition.

When blossom end rot develops and the calcium supply is approaching the inadequate level, here are some suggestions:

Do not add additional fertilizer containing magnesium, potash or nitrogen.

Make soil uniformly moist as soon as possible. Apply a heavy watering (one to two inches per square foot), if possible.

Practice timely and uniform watering until soil moisture is restored by natural rainfall.

Avoid disturbing plant roots when cultivating.

Mulch may be used to help maintain a uniform and adequate water supply.

If your tomatoes are producing flowers but no fruit, it could be because the nights were too cool. Later in the summer, temperatures can be too hot.

Research has shown that daytime temperatures above 90 degrees Fahrenheit or night temperatures above 70 degrees Fahrenheit result in decreased flowering and fruit set.

There is strong evidence that night temperature is the critical factor in setting fruit, with the optimal range being 59 - 68 degrees Fahrenheit. When night temperatures are out of this critical range, fruit set is reduced or absent.

Low temperatures reduce the production and viability of pollen. High temperatures (especially in conjunction with low humidity and moisture) can reduce fruit set because of pollination and-or fertilization failure.

"Growing Green" is contributed by Lehigh County Extension Office Staff and Master Gardeners. Lehigh County Extension Office, 610-391-9840; Northampton County Extension Office, 610-746-1970.