We live in Dundas, ON and had planted 6 pyramical cedars about 7 years ago to give us privacy from our neighbors. Last year we topped them as they were growing about 12 feet. We cut them down to 10 feet. After this past winter, all of the cedars are brown, but we noticed some green growth coming through in a couple of them and are hopeful, but do not know if they will survive. Is there anything we can do to preserve them?
It was a difficult winter for many plants here in southern Ontario. Prolonged and deeper soil freezing, arctic winds, and ice storm all caused a lot of damage such as wind burn, and some plants just couldn’t handle it. The early onset of the cold weather prevented many plants from taking up enough water to keep hydrated through the winter and they essentially dried out. That is what I suspect happened to your cedars. It is heartening to know that you see some green, so perhaps they are alive, but just severely damaged.
If you wish to keep the hedge, now is the time to give it a good shearing, and not just the outside, but between the shrubs too. Use a clean, sharp hedge shear and remove up to a third of the needles. Do not cut back to bare branches, as the lateral growth that may be stimulated will not occur at that point.
For more information on cedars and pruning read: https://mark-cullen.blogspot.ca/2010/09/cedar-hedges-investment-that-grows.html
In the meanwhile, there are a number of other things you can do to improve the health of your hedge. Cedars naturally grow in wet ground so regular watering is a must, especially in drought conditions. Watering must be deep so a light sprinkling on the top of the soil is of no use. Mulching is important to hold that water in the root zone, deter weeds and shade the roots.
Feeding regularly is important as well. A fertilizer that can be dissolved in water and applied directly to the root area will allow more of the nutrients to reach them. Topdressing with sheep manure compost or regular compost will not only feed the hedge but will also improve soil structure, encourage beneficial macro & micro organisms and the earthworms will love you forever.
If, after shearing and and a few weeks of TLC, the hedge still looks brown and dead, you may need to replace the trees. However, with a little patience those green growing sprouts will expand, and before you know it, the hedge is on it’s way to rejuvenation. Cedar can be sheared at anytime, so if there is further browning that needs to be removed, then do so when you spot it.