Watering Peonies - Water newly planted peonies promptly upon planting. Check the peony plant or root in a day or two to see if the root settled too deeply. Reposition it higher, if needed, by lifting it and placing more soil under it. Re-cover the root with soil. The peony eyes (buds) should be just an inch or two under ground level, with the roots going further down into the soil.
Baby peony plants in the garden need water to thrive – give them a drink every couple of weeks throughout their first spring, summer and fall (unless the rain does that for you). Keep the soil slightly moist, not saturated. I prefer the ground to almost 'dry out' between waterings.
As peony plants mature, they can thrive on less water and are rather drought tolerant, although a good watering now and then may be beneficial. Old established peony roots are quite hardy and often survive well with little or no watering (only rain water).
If you have peonies in containers, be sure to water them often during the warm days of summer. A container dries out fairly quickly and may need watering daily during high heat. The leaves will show stress when they are in dire need of a drink.