Our winters in Portland have historically been mild with just a few days of true cold, which typically hasn't required much extra effort on our part as gardeners. But in the age of anthropogenic climate change, more erratic weather patterns and dramatic temperature swings have become the new norm, making it important for gardeners to keep an eye towards the forecast to know when to take proactive steps to protect our beloved plants. When temperatures suddenly drop below freezing or remain there for extended periods, plants — and particularly less hardy ones — can sustain damage, which can sometimes be severe enough to kill them. But, thankfully, a little action on your part can help your plants successfully weather whatever the weather has in store.
Below, you will find a rundown on what to do when you spot unusually low temperatures in the forecast.
Protecting Your Plants
Don’t panic. Most garden plants will bounce back just fine from a cold snap, especially if they are reliably cold hardy in our Zone 8 climate.
Focus your energy on the plants that need it. Plants that are only marginally hardy in our zone will need the most help, along with those exhibiting tender new growth or swollen buds, which are more susceptible to damage from the cold than other plant tissues. Cold-hardy woody plants will likely survive a cold snap on their own, but this spring’s floral display may not fare as well without a little help. Having an outdoor thermometer or two posted in your garden will help you to pinpoint different microclimates across your particular site, which can further help you decide where to focus your plant protection efforts.
Move what you can. Relocate containers — and especially those planted with tender plants — to a sheltered location. Look for a brightly-lit space that stays above freezing, but that is not so warm as to shock your plants with a sudden transition. A garage or shed works great, as does a cool interior room, but even a location up against an exterior wall or under an overhang can provide some protection. Place hanging baskets on the ground, or move them inside to protect them from chilling winds.
Keep in mind that because their roots are more exposed to the elements above-ground, plants are less winter hardy when planted in containers than when grown directly in the ground. As a general rule of thumb, anticipate your plants to exhibit two full zones’ less cold hardiness in containers. For example, a containerized plant normally winter hardy to Zone 6b would likely fare just fine without protection during a typical Zone 8b winter, whereas a Zone 7b plant might struggle, even though it is nominally winter hardy here. If we are forecasted to experience a stretch of unseasonably low nighttime temperatures closer to the average minimum of a colder zone — say, Zone 7b’s chilly 5 - 10°F as opposed to our more typical 15 - 20°F — change your calculations accordingly when deciding what to protect.
Insulate the roots of plants in the landscape with 2-3 inches of mulch or compost, being sure not to mound any around the stem or trunk of the plants. Frost cloth can also be used to provide an additional layer of protection, but for plants often treated as annuals, this may not be enough.
Protect plants with leaves and flower buds from desiccating winds with frost cloth. In a pinch, old sheets and towels also work well as an insulating barrier! When cold temperatures are accompanied by the notorious east wind, the leaves of plants are more susceptible to desiccation and burn — especially the likes of Gardenias, Bamboos, Scheffleras, Pittosporum, Nandina, and hardy Bananas and Palms.
Give your plants a good drink before freezing temperatures arrive. A well-hydrated plant is one that's better able to withstand whatever Mother Nature can throw at it, and water itself can help to insulate a plant’s roots.
If snow is in the forecast, be prepared to lightly shake off small shrubs and trees if it is safe to do so. This is especially true of evergreens whose leaves or needles provide more surface area for snow to accumulate. While you don't want to disturb icy branches, which are more prone to snapping, preventing snow from accumulating and weighing down limbs in the first place can help your plants to fare better through winter weather. However, snow on the ground can actually help to insulate a plant's root zone, so it's best to leave it be.
With timely action, you can successfully protect most plants in your landscape from unseasonably cold temperatures. And even if hardy plants sustain damage from leaf burn, new growth will generally cover this in the spring. Of course, for a variety of reasons, this isn't always possible. Sometimes, in spite of our best efforts, a plant might not survive a late cold snap. All gardeners — no matter their experience level — have been there, and there's no shame in being bested by Mother Nature. In the event that this does happen, we always like to think of it as a good excuse to change things up and experiment with new plants in our gardens!
Winterize Your Garden
While you're prepping your plants for a cold snap, it's a good idea to double-check that the rest of your garden is ready, too. Make sure garden hoses are drained and stowed and that any outdoor spigots are insulated to protect them from freeze damage. And if you haven't already, ensure your fountains and birdbaths are winterized by draining them and removing any easily-damaged internal components like lights or pumps before covering them with a breathable, water-resistant covering. (Be sure to pull it taut to prevent rain and snow from pooling inside!)
Our backyard birds — including hummingbirds — could use a helping hand to get through particularly cold spells, too. Keep an eye on your bird feeders, as many species will begin to up their caloric intake even before the weather shifts. If you have a plastic feeder, that is preferable for cold winter nights, as feeders with metal perches may be too cold on birds' feet when temperatures dip below freezing. High-fat foods like suet are particularly useful for songbirds, jays, and woodpeckers looking to withstand the cold. And for hummingbirds, artificial nectar can be kept above freezing with a specially-crafted heater fitted to the bottom of the feeder, although we've seen other creative solutions, too, including incandescent string lights wrapped around the feeder to provide enough heat keep it above freezing. Other options include simply bringing your feeder inside at night, then putting it back in the morning so that fresh nectar is available to your backyard hummingbirds when they wake from their state of torpor and go searching for sustenance.
Not sure what to protect? Feel free to ask us by phone, or email a photo to email@example.com.