Local Trees and the November Freeze

Have you noticed many evergreens turning brown?

Damaged needles on Fir Tree, Niwot (Josh-Morin) — Damaged needles on Fir Tree, Niwot (Josh Morin)

The warm weather over the past couple weeks has gotten a lot of folks outdoors and enjoying the beautiful weather. While on strolls, hikes, and other outdoor activities, something noticeably wrong is standing out with the pine, spruce and fir. The usual backdrop of the evergreen foliage is contaminated with an off-green, yellow or even browning tint that isn’t normally experienced this time of year. Upon closer investigation, you can find the needle tips have turned to brown or yellow and, in some instances the entire needle has dried up to a crisp straw color. At Taddiken Tree, we are getting lots of calls asking about this particular issue. I don’t think many of us have forgotten the beautiful Indian Summer we enjoyed this past fall, with temperatures staying mild into November. Those warm fall temperatures meant that a lot of trees were still active and had not yet gone dormant. Then suddenly on November 10^th it all came to an abrupt end. When the temperature swing was over, Denver saw a drop of 77 degrees, the third largest temperature fluctuation recorded in Denver’s history.

Full and partial needle-browning on pine at Niwot Elementary School.

Trees have to spend their entire lives enduring whatever environmental conditions are thrown at them. In order to successfully survive temperature extremes, they need a period of time to adjust. This drastic temperature fluctuation gave trees no such time to adjust and what we are now seeing are symptoms of this severe stress. It’s hard to predict what the outcome of the freeze will be on many of our trees until spring arrives, but it’s evident that many trees are going to suffer from this event and this may even result in irreversible side effects. However, not all hope is lost, and now is not the time to start cutting down damaged trees. Trees are incredibly adaptive and many are likely to be able to survive needle drop and losing branches associated with the sudden freeze. Even if the needles on the tree are totally brown, it may not be dead. Checking the terminal buds to make sure they are tender and not dried out is one sign that the tree will push new healthy needles in the spring. There are some cultural practices and remedies that you can do to aid in the bounce-back of certain trees: Watering. Applying water to the base of trees isn’t just a practice for the summer months. Water is often scarce in our dry, Front Range conditions (note: 12 inches of snow is equivalent to roughly 1 inch of water for trees). Because evergreen trees transpire (lose water through their needles) year round, they have greater water needs through the winter than deciduous trees. A great way to help reduce stress is to provide supplemental water once a month in the winter. When the soil isn’t frozen, stick a screwdriver into the soil around the tree and gauge the resistance of the soil to the screwdriver. If it goes in easily, your soil is probably saturated enough. But if it’s difficult to push it into the soil, its probably a good idea to get out the gardening hose. You can soak the soil by letting water run on the root zone of the tree at a slow rate so that it is absorbed into the soil and not running off. It might be wise to let the hose run for about 20 minutes or so on four different sides of the tree. Make sure to select days above freezing to water, and the warmer the better. If this is too much work, you can also hire an arborist or landscaper to provide this service.

Full canopy browning of small Pine, Niwot Elementary School. (Josh-Morin)

Anti-desiccant spray. This treatment will help preserve water in evergreens, preventing them from losing moisture through their needles. This is a great winterizing practice and is often recommended for newer plantings, trees in dry soils, locations exposed to winds, and trees in new subdivisions. This is a practice that should be performed by a professional arborist. Proper fertilization. Applying the right nutrient solution to the soil in the spring can help improve new growth. The new growth will produce more energy for the tree and help the tree recover. That said, different trees, in different areas, with different histories require different fertilization recommendations. Therefore, it is wise to consult a certified arborist before dumping store-bought fertilizer on a tree. It is also a good idea to have a soil sample analyzed for more precise recommendations. Mulching. Putting a layer of mulch down over the root zone will add extra insulation, iprove soil quality and help with moisture absorption. Mulch thickness only needs to be about 1-2” and be sure to leave a couple inches clear at the base of the trunk. Mulch should never be piled up at the base of a trunk.

Pine with needle scorch in Boulder. (Josh Morin)

Trunk-wrap small, deciduous trees. Evergreens aren’t the only trees suffering from the freeze. Trunk-wrapping small, deciduous trees for the winter months will help reduce sunscald damage. This occurs when the suns ray heat up the bark on the south and west sides of the trees. This tissue then freezes when the temperature drops and the cells are killed. Evergreens aren’t the only trees that will be damaged by the sudden freeze. Many deciduous trees (those that lose their leaves in the fall) still had green leaves when the temperature dropped. Some of these trees have held onto their leaves and are now brown. It is likely that many trees will have dead branches in the spring and in some cases the entire tree may not recover. The cultural practices listed above are also a good idea for deciduous trees. For more information you can check out this extension fact sheet http://www.ext.colostate.edu/pubs/columngw/gr130504.html

Co-written by Adam Witte and Josh Morin Adam Witte is a Research Plant Health Care Specialist at Taddiken Tree Company. He is a certified arborist and has a background in entomology. Josh Morin is a Board Certified Master Arborist and owner/general manager of Taddiken Tree Company.

Local Trees and the November Freeze

Have you noticed many evergreens turning brown?

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