The question: I have a lovely tree peony that is currently in full bloom. The front two stems are quite thick and in danger of breaking off because the flowers are so heavy. I will have to trim the stems as the plant is going to pull itself out of the bed.
How much can I take off?
The answer: As a rule, never take off more than a third of a plant. Just trim it for safety at the moment and then prune more heavily after the bloom is finished. These are tough plants, so you only need five to eight stems a plant.
In the spring, cut out unwanted stems and limit the lateral buds so the plant doesn't get crowded. Don't prune the first few years.
If the plant is weak, remove all of the buds to let it build a strong root system. These plants last forever if treated properly.