The perennials in my garden with semi-evergreen leaves are still looking good, despite the below freezing temperatures, but the – 35° C (-31 ° F) temperatures that will come later this winter will test their cold hardiness. Alternating cold and warming spells can stress perennials, with the freeze thaw cycle. We usually get consistent snow cover from December to April, which helps to insulate the plants. I’ve found that adding a layer of deciduous leaves over them also helps insulate the perennials from a cold zone 3 winter.
Just before the snow comes, the leaves from the trees overhead cover the garden. The trees do a pretty good job, and I assist by helping to fill in the garden sections that are missed, covering the perennials up with the fallen leaves. All of the perennial crowns benefit from the winter leaf mulch, and the plants still holding onto their leaves will appreciate the above ground protection too.
Here is the fantastic foliage of Helleborus ‘Ivory Prince’. These are semi-evergreen, and will stay on the plants until spring, but that means that the severe temperatures, and drying winds can damage these leaves. Last year, the leaf cover kept the Helleborus in excellent shape until April, as well as protecting the crowns.
A thick leaf pile collects under the willow tree, and here it is on top of the Helleborus. I threw some extra armfuls over them. The slender willow branches placed over top help keep the leaves in place when the wind blows.
Heuchera (coral bells) can heave out of the ground over winter, but the extra leaf layer helps to insulate them. I had no heaving of these perennials last winter.
The Heuchera ‘Plum Pudding’ (coral bells) contrast with the deciduous leaves. You can see the wonderful burgundy coloured stem on these perennials, while the purple and silver colour of the leaves is even stronger from the cold temperatures.
In the above photo, the Campanula (bellflowers) are partially covered with leaves. Most of the bellflowers I grow are very hardy in zone 3, and survive fine without leaf cover, but the extra layer in the garden won’t hurt them.
When the snow melts in spring, and the temperatures get warm, I remove the protective leaf cover from the garden beds. This is the fun part of spring gardening, pulling back the leaf mulch to see what is growing underneath. Some of the leaves have broken into small pieces, and will decompose into the garden soil, forming part of the mulch. The rest is set aside to decompose and be added back later. The perennials will use the good nutrients in the leaves.
Although we’ve had a few nice weeks, the temperatures are consistently below freezing at night. The willow tree, which hangs on the longest, is losing the last of its leaves. While the intricate pattern of branches is outlined overhead, underneath the fallen leaves will blanket the garden, and help protect the perennials.