Tomato Flowering Problems
The main problem met with the flowers on tomatoes is the lack of flower set (pollination).
Outdoors this is rarely a problem as there is generally an abundance of pollinators in the form of insects e.g. bees.
Indoors however might be a bit of a problem, so manual intervention is sometimes called for.
Depending upon the plant group i.e.indeterminate varieties (vines) that form a cordon, or determinate varieties that form bushes, side shoot removal might play a part in how floriferous a plant can be.
For example: removing side shoots from indeterminate is normal practice but in determinate varieties this would result in no flowers.
Lack of humidity or excessively high temperatures e.g. above 38°C (100°F) can cause pollen to desiccate before it has a chance to fertilise the flower.
Conversely, low temperatures below 10°C (50° F) may result in poor pollination, this is more probable with outdoor culture.
Damping down greenhouse floors should produce enough air movement and humidity to fertilise the flowers and reduce high temperatures.
Leaving greenhouse doors open in warm weather will allow pollinating insects to enter, and the movement of plants by air currents should be enough to ensure fertilisation.
Similarly, lightly shaking the plant/s can disturb the pollen thus allowing it to be carried in the air currents within the greenhouse onto adjacent plants.
Avoid plants becoming overcrowded, always allow plenty of space between plants, locate them where they get maximum light, ensure that they are regularly watered (but not over watered), and fed at all times.