Blossom drop can be attributed to several causes, most often related to either temperature and / or stress.

1. 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.

2. 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.

It sometimes help attract more bees if you plant nectar rich flowers in your vegetable garden.

3. 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 fruit forms. Too much nitrogen encourages the plant to grow more foliage, not more fruit.

4. 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.

5. 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.

6. Keep your tomato plants healthy. Use good cultural practices and treat for disease as soon as symptoms appear.

7. 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. Once the initial crop is harvested, the problem should subside.