When to spray anti-desiccant on evergreens?

In New Brunswick, the ideal window for applying anti-desiccant to evergreens is late October through mid-November, once temperatures are consistently below 10°C but before hard freezes set in below -5°C.

Anti-desiccants (also called anti-transpirants) work by coating the leaf or needle surface with a protective film that reduces moisture loss during winter. This is especially important in NB because our winters combine freezing temperatures with drying winds — a brutal combination for broadleaf evergreens like rhododendrons, boxwood, and cedar hedges. The plant's roots are frozen and can't replace moisture lost through the foliage, leading to that telltale winter burn: brown, crispy foliage by March.

Timing is everything with this product. Apply too early (while it's still warm) and the plant is still actively transpiring — the coating interferes with normal function. Apply too late and the product won't bond properly to frozen foliage. In the Fredericton and Moncton areas, late October is typically the sweet spot. In northern NB (Bathurst, Campbellton), aim for mid-October given the earlier onset of hard frost. Saint John and the southern coast can often push into early November thanks to the moderating maritime influence.

Choose a day that's above 5°C with no rain forecast for 24 hours. The product needs time to dry and cure before freezing temperatures arrive. Most products (Wilt-Pruf is the most common brand available at NB garden centres) are water-based latex and will not bond properly if applied in freezing conditions or washed off before curing.

Which Plants Benefit Most

Broadleaf evergreens get the greatest benefit — rhododendrons, boxwood, holly, and mountain laurel are the priority. Cedar hedges (Thuja occidentalis) and yews also respond well. Spruce and pine generally have natural waxy coatings that offer more protection, but newly planted conifers in their first or second winter are worth treating regardless of species.

Practical Application Tips

Apply in a fine, even mist covering all foliage surfaces — top and bottom of leaves. A second coat applied 30 days later (typically December, on a mild day) significantly improves protection through the worst of January and February. Don't skip the undersides of rhododendron leaves — that's where the stomata are and where moisture loss is greatest.

One important caution: anti-desiccants are not a substitute for proper siting and species selection. If your cedars are in a wind tunnel or your rhododendrons are in a Zone 3b microclimate in northern NB, no spray will fully compensate. Burlap wrapping on the windward side combined with anti-desiccant gives the best protection for vulnerable plants.

This is a straightforward DIY task for most homeowners — a pump sprayer and a $20-$30 can of Wilt-Pruf covers most residential properties. If you have large established cedars or a significant hedge investment worth protecting, a landscaper can apply it efficiently as part of a fall shutdown service. New Brunswick Landscaping can match you with a local landscaper for fall winterization work — it's a free service covering all of NB.