Dying Emerald Cedars, Viburnum, and Berberis

(Question)

Hello,

  • Several Emerald cedars planted a year ago in the spring have turned brown suddenly and died–they have been watered throughout this summer weekly.
  • A 12-13 year old Viburnum flowered beautifully this spring, but branches have been suddenly drying up and dying.
  • A mature Berberis  that existed near the Viburnum suddenly died a year ago.

[Other things such as hostas, false spirea and other plants seem to be growing well in that area. Considering planting some upright yews as a hedge, but concerned about the soil in that area].

 

(Answer)

Losing several shrubs in the same area within a short period of time is very disappointing; one’s initial thought might be that there is a problem with the soil. The condition of your soil may certainly be an underlying concern, but there may be other factors that are also responsible.

Emerald cedars (Thuja occidentalis ‘Smaragd’) are attractive, reasonably-priced shrubs that are often used to create hedges. Toronto Master Gardeners receive many inquiries as to why someone’s emerald cedars are suddenly turning brown and dying, even after keeping them watered and fertilized during the growing season. To successfully grow healthy Emerald cedar hedges in Toronto, one must understand that Emerald cedars are usually grown and shipped from B.C. They grow and thrive in the Fraser Valley where the climate of consistent temperatures with ample rainfall differs significantly from Ontario’s. These cedars require consistent moisture, well-drained soil and full sun. “In order for Emerald Cedars to establish strong roots, they will need a constant supply of moisture for the first year after planting. A thick layer of wood mulch will help retain valuable soil moisture”. [https://www.theobserver.ca/2016/07/15/bc-tree-needs-plenty-of-moisture-and-moderate-temps]. Of course, the drought and record high temperatures that Toronto experienced this summer no doubt contributed to the demise of these cedars.

Although your cedars (planted last spring) seemed to be thriving, the cedars were probably not be getting enough sun due to the beech tree–they get sun from the east and west, but not the south.

See: https://www.torontomastergardeners.ca/askagardener/dying-and-browning-emerald-cedars/ and https://www.torontomastergardeners.ca/askagardener/dying-emerald-cedars/

The problem with your Viburnum may also be the result of Toronto’s lack of rainfall since the fall of 2015. It is important, not only with regard to conifers, to make sure that the shrubs get sufficient water before the winter freeze-up. The desiccating winter winds, usually from the NW, could possibly contribute to the dieback. Prune back the dead branches to the main stem; if that doesn’t help the Viburnum to recover next spring, then you may need to consider replacing it. It’s unlikely that it isn’t getting enough sun since you mention that it flowered beautifully in the spring.

The sudden death of your Berberis (Barberry) shrub is puzzling. Generally, it is a trouble-free and adaptable plant that can tolerate heat, drought, some shade and clay soil, although it does prefer well-drained soil. In some areas of the northeastern U.S., it is considered ‘invasive’ due to birds eating and spreading the seeds. Given its position in your garden with reference to the beech tree, it’s possible that as the tree grew, the Barberry was gradually getting less sun; with added stresses of the winter conditions for the past few years, it finally succumbed.

Although your soil is probably not ‘toxic’, you most likely need to address the condition of your clay soil. Basically, the addition of well-composted organic matter annually  is important to help improve the structure of your soil.  If you ‘feed your soil’ with organic material such as compost and leaf mulch, the soil will feed your plants and help to protect them from the fluctuating weather conditions we’ve been experiencing. See our Gardening Guide: https://66.209.177.85/~torontom/wp-content/uploads/2012/07/Improving-Your-Soil-Organically.pdf. Mulching around your plants (trees and shrubs) with any organic material such as chopped leaves, straw, pine needles and bark chips throughout the growing season will not only conserve moisture, but will gradually improve your soil structure. Simply raking your leaves, chopping them with a mower and then covering the exposed soil areas with them will be a first step in feeding and improving your soil.

All the best in rejuvenating your garden. Thanks for getting in touch with the Toronto Master Gardeners.