Long Winter Effects on Trees

Boxwood 1
Winterkill on Boxwood

This year the weather has been abnormal, even for Nebraska. We had snow in mid-October and the cold still hasn’t fully released its grasp on us. This causes us to rethink ‘normal’ weather but it also causes problems for our plants.

Plants are slow to start

Plants are in line with the weather for this year, not necessarily with the calendar. The cool spring has slowed down or even delayed spring leafing out of many of our plants. Some plants may not even be emerging yet, which is unusual for late May. Don’t give up on these plants too soon this spring. Give the plants until early to mid-June before replacing them.

Winter Desiccation

The colder temperatures this winter led to a lot damage to evergreen plants. You might be seeing browning in yews, boxwoods, and arborvitae. This damage is likely from cold temperatures and winter desiccation which occurs when transpiration from these trees exceeds infiltration of water through the roots. Wait until early June to do much pruning of these shrubs. Give the plants time to come out of the winter weather to ensure that all of the dieback is complete before pruning out the brown areas.

White pines have also turned color this year, showing quite a bit of orange-brown discoloration. This is a combination of cold weather and salt damage. Even if the trees are further away from a road, splashing from vehicles can make the salt accumulate farther away from the road than expected. White pines are also quite vulnerable to north winter winds which would cause also cause discoloration. I would not prune the white pines, they should come out of it, but it may be a while longer. Next year, to prevent so much winter desiccation, you can use an anti-desiccant in the winter months.

Seed Production in Maples

You may have also noticed problems in your maple trees recently. The calls I have received were people asking why their maple was turning brown and if it was dying. Usually the browning has been found in a particular location of the tree, often at the top. The rest of the tree is fine and leafing out correctly. The brown in the tree is actually the seeds of the maple tree. This year, the maples have produced a great number of seeds or samaras, often referred to as helicopters due to the way they float to the ground when they fall from the tree. The brown in the tree is due to the fact that these samaras are maturing and will soon fall to the ground, many have already begun to fall and litter the lawn.

The reason for this heavy seed production is the weather. This isn’t just from this year, though, it could stem back to last spring when there was a late frost that killed many of the flowers on maple trees. These trees developed more seeds this year because they were not able to produce seeds last year, according to Scott Evans from Douglas-Sarpy Extension. The cooler spring this year may have increased the high seed production this year as well. High stress events can lead to more seed production, the tree takes the stress as a signal to produce more seed just in case the stress is deadly.

Seed Production in Conifers

Spruce cone, Tom DeGomez, Univ of AZ, Bugwood
Blue Spruce Cone, Photo Courtesy of Tom DeGomez, University of Arizona, Bugwood.com

Many people have also asked about brown structures at the ends of the branches on their conifers. These structures are just the pollinating cones. The concern is whether they are bag worms because they resemble a small bagworm structure. Typically these structures would appear earlier in the spring and may not even be noticed. But with the cooler spring, the production of these small cones is coinciding with the time that we can start to see bagworms. This is a normal process for evergreen trees and nothing is wrong with them when these cones appear. Bagworms will likely be later this year than normal years due to the temperatures.

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