Winter desiccation of evergreens and winter protection guidelines Kate's Garden 227 Main St. Markham N Markham, ON L3P 1Y6 October 25, 2015
1. Expertise The following expertise is based on the site visit and an interview with the client (see the table below). Table 1. Actual conditions of affected plants (source: site visit and an interview with the client). Plant Description Japanese yew Seasonally showing symptoms of winter burn. (Taxus cuspidata) Degroot's Spire Cedar Significant needle drop and skeletonization. (Thuja occidentalis `Degroot`s Spire`) Nest spruce Partial needle drop, partial skeletonization. (Picea abies `Nidiformis`) The map below shows the site setting and the direction of wind. Figure 1. The setting of the garden beds and the direction of the wind. 2
Most of the affected plants are placed on garden beds facing southeast. It is important to notice that sun rises in the southeast and peaks out in the south, which will be a crucial element in the winter protection program. 2. Data collection Relevant materials were gathered in order to explain conditions affecting the site characterization and plants present. According to Bromley (2011), transpiration of foliage (especially during periods of strong winds) may cause winter damage. Important is the fact that recently performed studies show that Toronto area is located in the belt of circumpolar westerly winds (also known as the "westerlies") dominating the climate of the analyzed region (SENES, 2011). As the same source states, the belt extends from the Canadian Arctic to the American Southwest. According to Stantec Consulting Ltd. (2003), air masses affecting the discussed region are cold and dry (Arctic winds), and dry (Pacific westerlies), reaching their peaks in November (autumn) and March (spring). In addition, the main cause of transpiration (the loss of water through foliage) are also sunny winter days (Jull, 2015). In effect, foliage facing the southeast sun (see Figure 1) begins transpiration. As the same source states, despite the presence of sun, plants cannot take up any water due to the fact that soil is frozen. Therefore, considering the southeast exposure of affected plants, and the impact of excessive winds, the foliage dries and turns brown. According to Jull (2015) the most often affected evergreens include arbovitae, boxwood, false cypress, fir, hemlock, holly, juniper, pine, rhododendron, spruce, and yew. 3. Recommended guidelines The following practices were identified that should be considered to eliminate a gap in maintenance programs, enhance the health, and improve the appearance of plants (Jull, 2015): 3
1) pruning out dead, damaged, or dying shoots that are turning brown (should be done in mid-spring after the bud break; brown shoots should be pruned back to a living branch or a lateral bud), 2) no pruning on spruces (that replace needles at branch tips), 3) no pruning on evergreens in late summer (or early fall) due to the fact that new growth will not harden off, 4) transplant sensitive plants (especially yews) into northeast side of buildings (to avoid sun exposure in winter as it is happening on the wrong side), 5) replacement of evergreens in the spring (before the bud break) or in late summer (August, September), 6) application of 2-4 inches of mulch around evergreens (to insulate roots from water loss), 7) fall watering of evergreens (1" of water/week for established evergreens, 2" of water/week for freshly planted specimens in order to provide them with sufficient water for winter); however, watering in October does not reduce winter injuries (Swanson, n.d.), 8) no fertilization in late summer and fall (to avoid new growth stimulation), 9) application of anti-transpirantion products in order to prevent water loss (it is important to remember that those materials should be reapplied after each snow and rain); nonetheless, some studies have shown that anti-transpirant sprays are ineffective (Swanson, n.d.), 10) installation of burlap (snow fencing or canvas) screens to protect evergreens from desiccation (4'-5' tall stakes with burlap screen 2' away from plants; avoid covering the top of plants to eliminate ice and moisture collection within the canopy that could cause diseases). 4
References: Bromley B. J. (2011). Winter injury and protection of ornamentals. Retrieved October 25, 2015, from http://mgofmc.org/docs/winterinjury.pdf Jull L. (2015). Winter burn. University of Wisconsin - Extension. Retrieved October 25, 2015, from http://hort.uwex.edu/files/2015/01/winter-burn.pdf SENES Consultants Limited. (2011). Toronto's future weather and climate driver study. Volume 1: Overview. Retrieved October 25, 2015, from http://www.toronto.ca/legdocs/mmis/2013/pe/bgrd/backgroundfile-55151.pdf Stantec Consulting Ltd. (November, 2003). Terrestrial environment for the proposed portland energy centre. Retrieved October 25, 2015, from http://www.portlandsenergycentre.com/behind_the_scenes/pdf/docs/nov2003/pe C_Terrestrial-Final.pdf Swanson B. T., Rideout R. (n.d.). Protecting trees and shrubs against winter damage. University of Minnesota - Extension. Retrieved October 25, 2015, from http://www.extension.umn.edu/garden/yard-garden/trees-shrubs/protecting-fromwinter-damage/ 5