Is your evergreen tree or shrub not looking so green and healthy this winter? You are not alone.
Evergreen trees and shrubs such as holly, rhododendron, azalea, and laurel are noticeably distressed this winter. The leaves of many of these evergreen plants are discolored – light green, yellow, brown, purple and even black – and in some cases are falling from the branches making for a not-so-evergreen plant. So what happened? What gives?’
Photo 1 shows winter bronzing on a Mr. Bowling Ball Arborvitae. The foliage on the outside of the plant is cast in an orange hue and the interior foliage retains a nice green color. The exterior foliage will transition back to a nice green color in the spring and the new growth will be a nice green color. Photo 2 shows undamaged leaves of a Nellie Stevens Holly whereas Photo 3 shows foliage from the same plant that has winter damage. If the damage caused by cold temperatures is not too severe, these bad-looking leaves will be replaced by nice new leaves in the spring. If damage caused is more severe, entire stems and branches of this plant may have died and will need to be removed. Because of its sensitivity to our conditions in the Cincinnati region, Nellie Stevens Holly is not a variety of holly that White Oak sells or recommends. Photos taken by the author.
Some winter discoloration to the leaves of these plants can be expected from year to year and is not concerning – think of boxwoods and arborvitae that usually show some winter bronzing (leaves/needles take on an orangish hue that returns to green in the spring). However, this year the discoloration and damage to evergreen plants is more noticeable than it has been. The culprit? There is more than one – drought and extreme cold weather.
The above graph from the National Integrated Drought Information System shows drought conditions for Hamilton County, Ohio in 2022. As evidenced by the graph, Hamilton County experienced drier than normal conditions in October, November and December. Yellow areas indicate abnormally dry periods – beige areas indicate a moderate drought. The Y axis represents the percentage of Hamilton County that was experiencing those conditions. Through much of October, November, and December 100% of our area was experiencing abnormally dry to drought conditions.
The lack of precipitation during the October, November, and December timeframe likely affected evergreen plants. To stay healthy, evergreen plants need year-round precipitation to provide moisture in the ground that they can then access through their roots. The movement of moisture from the roots through the trunk and the stems to the leaves keeps the plant healthy and looking good through the winter. Lack of moisture for an extended period of time leads to plant health stress.
It isn’t just the lack of precipitation that has had an effect on evergreen plants – it is also the weather, more specifically the temperature. Recall the blast of arctic air we had around Christmas? The above graph from the National Weather Service shows daily temperature data for Cincinnati in the month of December 2022. The frigid northern air sent temperatures plummeting to dangerously low levels – well below zero degrees fahrenheit. It was downright cold! Now imagine if you were a plant and didn’t have the luxury of going inside to warmer temperatures and protection from cold blasts of wind!
Through the process of transpiration (it’s like a plant’s version of perspiring) plants move moisture from the roots through the trunk, branches, stems, and then out through the leaves. It is a beneficial process for plants. Valuable moisture that is transpired through the leaves is replaced by moisture in the ground through plant roots.
Heading into Christmas, our evergreen plants were already stressed by the lack of precipitation. The extremely low temps then froze any remaining moisture in the ground. At the same time, plants kept losing moisture through their leaves and uh oh, the result isn’t good. Evergreen leaves could not replace the moisture lost through transpiration because either there was none in the ground (drought) or it was locked up in a frozen state. As a result, the leaves of many of our beloved evergreen plants – hollies, rhododendrons, azaleas, and laurels, look disheveled, distraught, peaked, and downright ugly. Some leaves may have even fallen off the plant entirely.
So have you noticed this with your evergreen plant and if so what should you do? For now, do nothing. You’ll know this spring if your plant has survived the perfect storm of the winter blahs. If your evergreen has survived, the damaged leaves/needles will fall off and be replaced by new healthy leaves/needles. Cut away any dead branches and throw these away along with the fallen leaf debris. Then fertilize the plant with the appropriate product. White Oak recommends Holly Tone or Plant Tone depending on the plant. Fertilize in April and use according to instructions on the label.
If your evergreen plant didn’t survive the perfect storm of winter blahs, consider replacing it with a hardier species or variety of evergreen. For example, not all hollies are cold hardy for the Cincinnati area – some are better than others. In general, hollies don’t grow well everywhere in our area. These are better suited for suburban sites that are protected from cold winter winds. Other more hardy evergreens, such as Green Velvet Boxwood, Gin Fizz Juniper, Soft Serve False Cypress, and our native Eastern Red Cedar are better suited for our conditions.
@whiteoakgardens