Dying Emerald Cedars


I’ve had three different sets of emerald cedars die, I’m talking about 30 of them each time. All planted by a long-standing professional landscaper, who is also puzzled. Proper watering, planting depth, etc. have been followed and even modified to try and find a solution, all with no luck. From what I’ve recently read the only thing that wasn’t done was keeping the mulch away from the trunks. The soil is clay, located in Southwestern Ontario and the tree lines run East-West. These trees, in two separate locations on the property, are bordered by a solid vinyl privacy fence on the South side. Would this have anything to do with it?


Thanks for contacting the Toronto Master Gardeners.

It is certainly unfortunate that you’ve not been successful in growing Emerald cedars (Thuja occidentalis ‘Smaragd’) on your property in SW Ontario; furthermore, you have tried several times.  Even though these attractive trees are native to North America, many available for sale in Ontario are actually grown in B.C. where the climate is generally cooler and the rainfall plentiful; one can often buy these inexpensively. Transporting these trees from B.C. to Ontario adds to the stress that these trees must undergo to adapt to a different climate (summers with higher temperatures and drought conditions); the probability of success is lessened.

You are aware that Emerald cedars need consistent/constant moisture to help them become established–water deeply and thoroughly at least twice per week. The use of a mulch helps to retain the moisture around the roots and keep the temperature more constant. And it’s essential that watering continue until the ground freezes in the late autumn. Unlike deciduous trees that go dormant during the winter months, conifers do not; once the ground is frozen, the cedars cannot take up any moisture to replace what is lost from the foliage that becomes desiccated due to cold winter winds. It’s also possible that the solid vinyl privacy fence on the south side of the cedar hedge may have a negative effect; since the winter winds generally come from the NW, the fence may be ‘trapping’ the wind around the cedars and causing further damage to them.

It’s time to consider other options–although the more common Thuja occidentalis (Eastern white cedar or swamp cedar) may not be as full or attractive as the ‘Smaragd’, it grows well in our climate. Another option may be some form of yew (Taxus), although they tend to grow more slowly that the cedars. Please see the references below:

We understand your disappointment and concern trying three times to successfully grow the Emerald cedar. However, we do hope that this information will help in understanding and appreciating the challenge of growing them in Ontario.  https://www.torontomastergardeners.ca/askagardener/dying-and-browning-emerald-cedars/