Answer: Take heart! You are doing a lot right. We just need to get those tomatoes to cooperate. There are several causes of failed bloom set on tomatoes including temperatures too high or too low, poor pollination, and excessive nitrogen.
Since your plants have not set at all since early spring, I think we can eliminate temperature as the cause. Poor pollination occurs when plants grow in a location protected from the wind. Wind shakes the tomato bloom causing pollen to fall within the flower and pollenate itself. Greenhouse tomato growers shake plants or blooms daily to help them pollinate.
If you feel this is not the cause, I would consider excess nitrogen. Heavy fertilizing early in the tomato growth period can result in luxurious vine growth at the expense of fruiting. Wait until plants begin to set fruit and then you can push them along with extra nutrition.
Another consideration is variety. Some varieties may not be adapted to your site. The giant types for example, are not known for setting many fruit in our hot, southern climate. Good choices for the Metroplex would include Celebrity, Dona, Champion and Early Girl Improved.
Finally, I would stop using the bloom set. Although this product can help at times, it is not necessary to grow tomatoes and it obviously isn't helping your situation. Also, you didn't mention the amount of sunlight the plants are receiving. They need at least 6 hours to do well.
Good luck with your plants and I hope your next crop is a bumper one! You'll soon find that one of the lessons of gardening is that each season is different. What fails this year may succeed next.
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