You know it’s raining hard in Vancouver when…the wind is blowing steadily in the southern part of the Okanagan Valley. Such was the case on Grey Cup weekend when winds blew constantly for two days, making for the perfect excuse to stay indoors and graze on snacks for four hours as the Lions brought home the silverware.
Late November usually brings this type of weather to the southern part of the province. We have the phenomena known as the subsidence effect to thank for this. Moisture-laden air from the Pacific hits the coastal mountains and drops heavy rain on the ocean side as it rises, then it drops down the other side, picking up speed and treating us to a gusty and dry day.
If you don’t think it’s dry, spend the entire day outside and note how your face feels like you’ve been too close to the fireplace. Plants can get the same feeling, especially conifers and broadleaf evergreens. I slap on a moisturizer before and after work on windy days; plants don’t have that option.
Plants need to be able to draw moisture out of the ground through their roots to prevent what’s known as desiccation injury. This occurs when water is lost from evergreen foliage to the air faster than it can be replaced through absorption of water by roots. The result is tissue mortality, where leaves look as through they’ve been burned.
This is why we harp on our customers in the fall to make sure that the soil around plants like rhododendrons, euonymus, chamaecyparis and others is good and moist before their irrigation systems are shut down for the winter. Water well in the days leading up to blowouts or freeze-up because when late November arrives and the inevitable winds arrive those plants will need that moisture to replace that which is lost into the atmosphere.
The problem becomes even greater as we move further into winter when the ground is frozen and the winds are blowing. At this point it doesn’t matter how much water is in the soil, it’s locked up in solid form. Winter hardiness doesn’t factor in either. Even Mahonia aquifolium (Oregon Grape), a native shrub which is hardy down to -30 deg. C, suffered from desiccation last winter where it was exposed to wind.
The solution in this case is to water in midwinter when, or if, temperatures are above freezing. If this doesn’t happen there are two other alternatives.
One is to wrap plants loosely in burlap. This will at least reduce the wind speed around the plant while still allowing air to move. Burlap is ideal for this because of its loose weave.
A second alternative is to apply an anti-dessicant product like Wilt Pruf to the foliage of the plants when the air temperatures have cooled into the single digits, but haven’t gone below freezing. This product will coat the foliage and prevent transpiration, the loss of moisture into the air, from occurring. It can be reapplied in midwinter when the temperature goes above zero.

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