I live in Toronto. Do peony shrubs need to be covered in winter with burlap or can they be left to the elements?
There are 3 main types of peonies (Paeonia):
- Herbaceous peonies, which die back to the ground each winter (or after a heavy frost in the autumn, they should be cut back to 7.5 cm (3 inches) from the surface of the soil to avoid fungal diseases that might overwinter) and require very little care; and
- Woody-stemmed tree peonies (Paeonia suffruticosa), whose stems are exposed to the ravages of winter. These are hardy, don’t cut them back at all. Foliage and flower buds may be susceptible to late frost.
- Intersectional hybrids (called “Itohs”), which are a cross between a herbaceous peony and tree peony.
The bottom line is that herbaceous peonies, Itohs and tree peonies grown in Toronto are cold hardy do not need winter protection. It is important to note that peonies need winter cold in order to flower.
The issue of mulching may be of interest. Some experts recommend not mulching peonies at all; in particular, with herbaceous and Itoh peonies, the mulching could make the top of the root too deep, such that the shoots (“eyes”) that form at the top of the root (crown) are not exposed to the winter cold – preventing the plants from flowering. However, with tree peonies in very cold areas (zones 2 or 3), it is appropriate to mulch the plants in the winter, to help prevent the repetitive thawing/freezing that can damage the roots. Remove the mulch in the early spring.
The Canadian Peony Society recommends that you mulch your peony for the first winter after you plant it, and remove the mulch in the early spring, when the first roots are visible. This also applies to Itohs.
Some gardeners put straw around the stem of the tree peony and wrap the plant in burlap, to protect flower buds from late spring frosts. The burlap should be removed gradually as the temperature increases. However, most people don’t bother to protect their tree peonies, and the plants remain happy and healthy.
If your peonies start to sprout in the early spring and a heavy frost is coming, you can put an upside-down pot over the plant until the frost is over, but this is generally not necessary, as the plants are frost-hardy and blossoms should still appear.
Here’s a good overview of taking care of peonies, from the North Carolina State University, Cooperative Extension Service: Peonies for the home landscape
And the Canadian Peony Society has a terrific website, with information about care of peonies.