After this brutally frigid winter, with sub-zero temperatures for days on end and weeks filled with ice and snow, our treasured, tender gardens have taken a really hard beating. We had hoped that they could slumber sweetly under a deep blanket of snow during the worst of the below-zero weather, but alas, the snow deserted us on the last icy polar blast.
According to the National Weather Service, St. Louis accumulated about 50 hours of below-zero weather this season. It is the worst winter in decades. We have had all of the conditions that gardeners dread: limb-breaking high winds, abnormally cold temperatures for days at a time, and lower-than-normal precipitation going into the cold zone, so that some broad leaved plants have suffered more desiccation than usual. But don’t think that global warming is gone. Worldwide, this winter, was the seventh warmest ever. We were just the unlucky ones to get smacked by a wide-swinging polar vortex. I fear that this may be a more common concern for the future as all of our global weather patterns shift with climate heating.
Sneaking into Zone 7
As climate change has given us warmer and drier summers, we have reached south to the zones below us and pulled northward many lovely Southern landscape plants like crape myrtles, camellias and hardy bananas. Some of the improved winter performance has been due to a long string of warm winters, and our zone average has surely moved to 6 from 5. If a plant endures this winter, we should be happy to add it to our permanent planting palette.
In my own garden, I will be watching the heavenly bamboos (Nandina) that were just planted last summer. Using both dwarf and standard forms, I would be less concerned about them if they had been in place for four or five years first. Right now, half of them looks completely dead and the other half looks like the parts below the snow line may pull through. Another marginal plant for us is acuba (Acuba japonica). This broad-leaved evergreen has yellow-speckled emerald-green leaves. It makes a great container filler and may even root when used in arrangements. Checking on mine today, the top leaves (above the snow line) look like dried tobacco. The lower leaves are tired by still offer about half living tissue and the main stem is still a bright happy green. Time will tell!
Deciduous shrubs will likely be late to leaf out this spring, so do not prune them too early. The soil will stay cold longer than usual. Don’t give up on a plant as dead until you are sure. For a vitex or hydrangea, that may be well into June. Any plant that you normally prune back in the spring, go ahead and cut as you typically do. As the buds finally swell, you may re-prune to the appropriate joint. You can tell a bit by using your thumbnail to scratch into the bark to see if it is green. If I were a betting woman, I’d likely count on established hydrangeas and viburnums to be fine, but late.
Broad-leaved evergreens took a real beating this year. The drying winter winds and low humidity caused them to dry out completely. Most of the tender boxwoods at the Garden are still under cover, and we must wait longer to see how they fared. For unprotected boxwood out in the community, I am sad to report about 50 percent mortality now, more to show as warm weather stresses weak plants. And for those of you nursing climbing fig or variegated ivy outside, do not look for them to return.
If you have ever tried to manage a coastal garden, you know that plants hate salt spray. The damage shows up as brown or yellow dropping foliage, tip die back and whole plant mortality. The extensive amount of ice this winter caused us to use much more de-icing salt than normal. As this salt goes into solution with the melting ice, it forms a saline runoff that goes downhill. Particularly vulnerable to salt damage are our evergreens, and white pines are notorious for turning yellow from too much salt.
If you have used a lot of salt on your own property or are near a street that has been salted frequently, look for where the runoff flows and where the spray kicked up by tires drifts. As soon you can hook up a water hose, set the sprinkler to wash off the foliage of plants in these areas. The more water you can flood through the soil, the faster you will wash the salt on downstream and reduce the damage done to the plants in your garden. Salt damage may show up slowly, with the worst necrosis occurring by mid-summer. Even if you see no damage yet, please try to rinse the salt away to prevent it from occurring.
Schedule Tree Inspections Now
Have your trees inspected this year by a certified arborist. The weight of ice and snow can cause splitting in the main crotches. Couple the ice with high winds, and we should anticipate a fair amount of tree damage this spring. Caught early and diagnosed properly, some of these injuries can be treated by corrective cabling and pruning.
The Proof is in the Pudding
Julie and I would be interested to receive reports from those of you who grow figs, hardy bananas, camellias, vitex and other borderline plants. Tell us about how they have survived this brutal winter. Please include information about varieties, location, growing conditions and any winter protection you have added. This season will be a great learning opportunity for all of us.
We look forward to your comments. And for anyone who can provide a photo of a surviving hardy banana, could I get a pup from yours? Everyone needs to be patient this year and wait, wait, wait. When those tender basal shoots finally emerge, feed them lightly. Keep everything watered well this summer and gentle your green babies back to health. If they made it through this winter, they deserve a little pampering. Write to us at LNLandscape@mobot.org.