We have some mature cedars along the borders of our backyard that are withering. We want to fill in some of the “bald” spots, which are shady, with new 5 – 6 feet cedars. When is the best time of year to plant cedars? What type grow best in shady areas? And what should we do in the first month or two to help them grow and thrive? Thanks
Hello and thanks for contacting Toronto Master Gardeners with your question.
True cedar trees such as Atlas cedar (Cedrus atlantica) belong to the Cedrus genus. Arborvitae or false cedars in the genus Thuja belong to the cypress family. You probably have Thuja occidentalis, also known as Northern white cedar, Eastern white cedar, or arborvitae. It is native to eastern Canada and much of the north central and northeastern United States. They all do best with 6 hrs full sun per day and moist but not waterlogged soil. I would suggest pruning the cedars in your hedge and some overhead branches of other trees, if that’s an issue, to allow more sunlight to fall on the bald areas. The cedars there have probably failed because of the shade. If you open the area up, you can plant more Thuja occidentalis and have a nice uniform hedge. Evergreen shrubs and trees that do well in shade and part shade are yew and hemlock and they would be options for planting as well.
Cedars prefer moist, organic, well drained soil. So in the spring when it is time to plant them, adding some compost to your soil if it is sandy or heavy clay and mulching around them (but not up against the trunks) will help to maintain the appropriate amount of moisture in the soil. Frequent watering is the best thing you can do to ensure the success of your new plantings, whether cedar or not. Each tree should receive 1 pail of water, poured on slowly, 3 times a week during the heat of the summer. They should be watered a little in the fall too, right up until the ground freezes. Because the trees are evergreen, they respire on warm days during the winter.
Here is a link from the Missouri Botanical Garden that provides information about a cultivar of Thuja occidentalis, a commonly used cedar for hedges or privacy breaks in the Toronto area.
https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=m550
28/03/2021