Depending on what’s growing in your garden, there’s a lot you can do to prepare your plants for the colder months ahead. By overwintering certain varieties, you can avoid having to buy all new plants next spring and ensure they thrive year after year. We’ve got the low-down on how to make sure everything from your perennials to trees are ready when the snow falls.
What is overwintering?
Overwintering is the process by which some plants react to “winter” conditions such as sub-zero temperatures, ice, and snow. Some varieties need no intervention while others will require special care in order to survive the winter.
What needs to be overwintered?
Generally most perennials need an annual ‘hard prune’ which is when you cut off main stems so as to promote vigorous growth of newer and healthier stems. This technique can be carried out in the spring or in the fall, however cutting back in the fall helps perennials jump right into new growth come spring.
Simply take a pair of garden sheers and cut off all main stems to about 2-6” above the ground before the first frost. Some common perennial varieties that require to be cut back include ornamental grasses, daylilies, daisies, irises, hostas, etc. If you are unsure, you can simply run a quick online search.
In some cases like with lavender and ornamental grasses, you can further insulate the root system by simply covering it with mulch or straw.
The majority of shrubs are virtually care free during colder months as they enter winter dormancy. There are however some varieties of shrubs that are considered sensitive, meaning they might not survive the winter in certain hardiness zones and will require special care. In Ottawa, our zones are considered 4B-5A. Varieties belonging to zones 5B and up will be required to be wrapped top to bottom using white thermal felt and secured using rope. This should be done before snow falls and remains on the ground.
It is crucial to use white thermal felt and avoid all dark coloured cloth such as black or green felt as well as burlap. Dark fabrics are known to attract the sun which absorbs heat thus causing your plant to come out of dormancy and possibly causing it to burn.
You can review NRC’s Plant Hardiness Zone Maps which provides insights about what can grow where.
If you are unsure what zone your shrub is in you can find this information by running a quick online search. Common varieties that are outside of our zones and require special care include boxwood, butterfly bush, yew, some roses, and Japanese Maples. Note that columnar cedars and junipers should not be wrapped as they are hardy enough to survive our winters.
Mature trees do not require any special care during colder months, however trees having been planted within 5-10 years should be wrapped. By doing so, you are protecting it from being eaten by rodents such as rabbits as well as protecting it from sunscald.
Using white thermal felt, wrap the tree from the trunk to as high up as possible. Plastic wrap spirals can be used to protect the trunk.
For trees with multiple stems that are difficult to wrap such as evergreens and columnar trees, you can build a parameter using chicken wire and stakes to keep rodents, rabbits and deer away.
We highly recommend your trees (especially evergreens) be given one last good watering between mid-November to early December. By doing so, you are ensuring that it does not go thirsty thus preventing the foliage from browning due to desiccation.
Even though overwintering might seem like extra work, it can save you both time and money in the long run.