My oleander trees (both in very large pots) are now two years old. They made it through the winter and bloomed out beautifully in the spring. Last year they bloomed nicely also but didn't drop the flowers like they are doing this year. There's plenty of flowers but almost as many on the ground that are on the trees. I didn't have that last year. since I've noticed a difference, I was wondering if it was something I was doing, or lack of, that could be causing them to lose their flowers. Thank you for any suggestions.
Check for signs of any pests or insects, though Oleander are generally not bothered by insects.
The behavior sounds actually quite normal for the plant.
Pruning your shrubs right after they are finished blooming will help them develop new growth and better flowering the following season.
Remember that all parts of the plant are poisonous and the dropped blossoms should be cleaned up to lessen the risk to people and pets.
Here are some links to help refresh you on the care requirements.