In spring and fall, water but don’t overwater!
If there’s one thing peonies don’t like, it’s being over-watered. Over watering can easily lead to root rot. But that' doesn’t mean peonies, especially newly planted peonies don’t need a drink once in a while!
Soil that remains soggy and wet for an extended period of time is a death sentence for peonies. Well-drained soil is so important and overall, dry conditions are much more favorable to peonies than wet conditions. The large roots of an established are able to store water very efficiently to overcome drought.
However, watering in the fall and spring can be crucial toward the health of your new and old peonies.
In the spring, water is important to supply the newly sprouted and growing leaves, stems, buds and flowers.
In the fall, the roots systems of your peony become active. This is when your peony will build its foundation, growing new roots to support itself through the coming season.
If Mother Nature doesn’t supply you with water in a week’s time this fall, it’s a good idea to give your peony a drink. Another good measure is to dig into the soil a bit with your fingers, if it’s still dry soil and inch or two down, it’s time to water. A low steady stream is more beneficial than one big pour, but do what you can! Do this all the way up until the ground is frozen.
If you’ve gotten some good rain, let it be. And most importantly, don’t stress too much! If the soil feels dry, give it some water. If it feels moist, leave it.
A note about fern peonies: Fern leaf peonies typically go dormant earlier than other peony varieties and even more so do not tolerate too much watering. Only if the weather has been very dry would I suggest watering your fern leaf peony, otherwise just let Nature support it.