I have three tri colored beech trees which I successfully planted last year. Question: Almost all trees and shrubs have leafed out and blooming, but my beech trees remain dormant. When can I expect them to break dormancy? Does this variety typically leaf out vary late? Thanks
Thank you for contacting the Toronto Master Gardeners.
The timing of leaf-out can vary widely between different species. Originally it was believed that leaf-out was predominantly controlled by temperature, with plants generally leafing out earlier in warmer conditions; however we now know that a warm temperature is not the only factor. In fact, for many species it is a combination of warm and cold temperatures along with day length that dictates when the leaves will emerge from the bud. For example, our sugar maples have a chilling requirement, meaning that they require a certain number of cold days in the winter before buds are able to break dormancy.
According to an article from the Arnold Arboretum (Leaf-Out Dates Highlight a Changing Climate), the exact number of cold days required depends both on species and on the weather of the preceding growing season. Once the required number of cold days has been fulfilled, then a certain number of warm days above a certain threshold temperature are needed for leaf development and eventually bud break to begin.
Stem anatomy may also play a key role in leaf-out strategies, as the smaller vascular structures of early-leafing trees allow them to withstand the freezing temperatures that sometimes occur during early spring. Leaf-out timing can also vary within each species. A beech tree on a warm, sunny hillside may leaf out before a beech in a cool, shady ravine. Furthermore, the timing of leaf-out within each species is weather dependent and can vary dramatically from season to season. A short winter and warm spring may coax greenery into appearing long before its typical leaf-out date.
I wouldn’t despair yet with your tricolour beech trees. In my Markham garden, my Ginkgo, Katsura, Paperbark Maple, Yellowwood, Redbud, Weeping Beech, Japanese Bloodgood Maple and Sunburst Locust have yet to leaf out. Whereas my Seven Son Tree ( Heptacodium miconioides) is in full leaf.
If you are concerned and want to know if your trees are still viable, scrape away a bit of the bark with your fingernail. If you see green underneath the bark, then the tree is still viable.
The following link provides an excellent article from the Arnold Arboretum on climate and it’s effect on leaf out: