Tree peonies are quite resistant to drought. However, to guarantee instant growth of the capillary roots in the examples just planted, it is advisable, in spring and in the absence of rain, to water the soil at least once and no more than twice a week.
Over the years to follow, watering grounded plants will be necessary only during long period of drought, particularly in the periods before flowering. In the absence of rain, potted plants are best watered twice a week, but only when the soil dries up between one watering and another.
Avoid using flowerpot dishes at all costs, as they favour water stagnation and will quickly cause the roots to rot. Never wet the leaves, which could later suffer from disease. Avoid also drip watering, which would keep the roots damp at all times, with the risk of them rotting.
If the tree peony should be planted in a lawn with an irrigation system, avoid watering them every day or every night when temperatures exceed 15°C. In fact, excess humidity, besides destroying the roots, could also damage the foliage and expose the plant to the risk of grey mould.
A tip: when creating mixed borders, it is best to avoid planting peonies next to plants that require frequent watering, like hydrangeas or azaleas which, moreover, need a more acidic soil than peonies.