What to Do About Wacky Warm Weather

March 26th, 2024

   Another warm winter has faked the landscape into acting like we’re farther ahead on the calendar than we really are.

Ahead-of-schedule buds and blooms are more susceptible to this kind of cold damage than plants that maintain their winter dormancy longer.

   That’s not a problem if the weather course stays full steam ahead. So long as temperatures don’t nosedive in the coming weeks, the upshot is that we’ll simply have an early spring. Plants will bloom earlier, and growth will advance sooner than usual into a normal growing-season pace. No problem.

   The trouble is if the weather decides to back-track into traditional norms or less… or worse yet, yo-yo’s between abnormally warm and abnormally cold. Plants like sudden change even less than people.

   The way it used to work most years, plants stayed dormant long enough to protect themselves against early to mid-spring freezes. But when flowers and buds open early due to the kind of sustained warmer-than-usual temperatures we’ve been having in recent winters, they lose some of that protection.

   Open flowers or too-far-along leaf buds are much more susceptible to cold injury. Temperatures that they would have sloughed off while dormant can cause damage to this advanced growth.

   Sometimes a few degrees can make the difference.

   Smaller bushes can be draped overnight with a floating row cover or sheet to give a few degrees of protection in a frosty forecast, but there’s no good practical solution to help a 20-foot tree. (Orchardists run misters all night.)

   If the worst happens, cold-killed flowers will result in few or no fruits (on species that produce fruits and berries), while prematurely advanced leaf buds can result in browning around the leaf tips and margins.

   We’ve seen that happen several times in the last decade as our winters have warmed but early spring didn’t get the memo that the buds were beyond dormancy.

   Plants normally grow through these setbacks, but it’s a blow to that year’s performance.

   This wacky up-and-down stuff (not to mention even a single very cold snap in the middle of an otherwise warm winter) is also enough to cause browning on evergreens – especially broad-leaf ones like azaleas and boxwoods.

   If you’re seeing some brown, brownish, or even bare evergreens, don’t despair. They may not be mortally injured.

   It’s very possible the damage is limited to the foliage – i.e. the leaves and needles that are the plants’ extremities and therefore most vulnerable to cold, wind, and winter drying.

This variegated boxwood may look bad now, but there’s a decent chance it’ll drop the cold-damaged foliage and “green up” later in spring.

   If the branches – and more importantly, the roots – are unharmed, plants often go on to grow fresh foliage in spring and/or push up new shoots from the ground and base of the plant.

   Two key factors correlate with the amount of evergreen damage.

   One is the type of plant – specifically, how “winter-hardy” the variety is. In other words, how low can temperatures go before that species typically experiences damage?

   Plants that are borderline-hardy to the Harrisburg area are most at risk, such as the broadleaf evergreens aucuba, nandina, camellia, variegated English holly, and osmanthus.

   Other species are “semi-evergreen” here, meaning they stay green in warm winters but can brown and drop leaves in cold ones. Examples are sweetbox, box honeysuckle, and leucothoe.

   In other words, genetics is the explanation. The more cold-hardy a species, the less likely it is to experience damage when temperatures dip down to our traditional lows.

   The second key factor affecting damage levels is the cultural situation of each plant. This includes where you’ve planted the plants, how old they are, and the care they’ve received.

   A borderline-hardy aucuba, for example, might be completely brown in an open, windy site while one planted next to the heat-absorbing brick or stone of a heated house might look much better.

   Young plants are also more susceptible to winter cold since their root systems are less developed and they’ve had less time to adapt to a site’s soil and microclimate.

   And third, plants planted in good soil with adequate nutrition and kept well watered (especially heading into winter) tend to fare much better than plants dug into lousy clay and ignored.

   The best scenario is that any sickly-colored evergreens you’re now seeing will simply “green up” once warmer weather arrives.

   Plants with more extensive browning are likely to drop the damaged foliage, which can look alarming. But even then, so long as it’s just been the foliage “shocked” by the wacky weather, the roots and branches will get busy generating a new set of leaves.

   I’ve seen hollies that were almost totally bare by March look reasonably good again by summer and back to looking as good as new two years later.

   A notch more serious is plants that have suffered damage to their branches as well as the foliage. In this case, new shoots and foliage still could emerge from the live inner and lower wood of the plant.

   Assuming that’s the case, you should be able to trim back to live growth and/or prune out any branches that have died altogether.

   Even if all of the top growth has been killed by winter cold, there’s still a chance that the plant will generate new shoots from the surviving roots below ground.

   The worst thing you can do at this point is assume a sad-looking evergreen has died and dig it up.

   Patience is the treatment here. Wait until at least May to see how much natural recovery occurs.

   You may need to do nothing. Or you may need to do a little pruning once you see for sure what’s alive and what’s not.

   No need to spray anything, fertilize, or take any other action at this point.