Are your evergreens looking yellow or brown? This might be why…

Extreme temperature changes over short periods of time during winter months can leave evergreen trees looking a little yellow and sad. There are a number of different reasons an evergreen tree might be turning yellow/brown and/or dropping needles this time of year. Sometimes it’s perfectly healthy, other times it’s not. How do you tell the difference, and what should you do? Here’s a few tips:

This pine is showing needle cast. Notice the brown needles are lower on the branch while the healthy green needles are closer to the tip.

This pine is showing needle cast. Notice the brown needles are lower on the branch while the healthy green needles are closer to the tip.

Needle Cast: If your conifer (pine, spruce, fir, or juniper) is dropping needles, it may be a perfectly normal and healthy occurrence. If the needles that are dropping are only on the interior part of the tree while the needles toward the ends of the branches are still flexible, green, and firmly attached, then your tree is going through a process called “needle cast.” This process is kind of like deciduous trees casting off their leaves every fall – the needles deepest inside the tree no longer receive much in the way of sunlight as they are shaded by the newer exterior needles, so the tree drops them. This is totally normal and you should not be alarmed.

Sun Scald: If the needles on one side of the tree are showing yellow or brown coloration, but the other side of the tree still looks healthy, it could be suffering from sun scald. The exceptionally dry winter air combined with low soil moisture and intense sun causes the needles to dry out. The damage is often only present on the most exposed parts of the tree where prevailing winds or southern sun can have the greatest impact. Often, only the tip of the needle will be discolored while the base of the needle remains green.

Some of this damage may be inevitable, depending on the location of the tree, but it can be mitigated by good winter watering (click here for more on winter watering). For particularly sensitive evergreens like boxwoods, arborvitae, and oriental spruce, to name a few, a permeable fabric like burlap can be used to wrap the plants, providing a little extra protection. Trees can also be treated with Wilt-Pruf, a product designed to give evergreen plants an added layer of protection on their needles and leaves. Generally, this type of damage is only short-term. Only in extreme cases do we start to worry about the overall health of the tree.

Freeze Damage: If your tree is dropping needles or yellowing/browning uniformly around the entire plant, there’s a chance the recent deep freeze caused such a shock to your tree that the needles were damaged.

Fort Collins Weather Nov. 2-15, 2014

Extended periods of warm weather followed by rapid temperature drops is the perfect formula for evergreen freeze damage.

Freeze damage on a Southwestern White Pine. Note the damage is present on the tips of branches while the interior needles remain green.

Freeze damage on a Southwestern White Pine. Note the damage is present on the tips of branches while the interior needles remain green.

When plants go through such a rapid change in temperature, they don’t have time to undergo the physiological changes that help them tolerate the cold. Cell walls can rupture when they freeze and the dry air can cause damage more easily than would otherwise be the case. In instances like this, the damage will be most prominent on the outer parts of the branches, causing the tips to discolor and lose needles while inner needles that weren’t as exposed during the freeze remain green.

Freeze damage on a Southwestern White Pine. Note the damage is not limited to just one side of the tree.

Freeze damage on a Southwestern White Pine. Note the damage is not limited to just one side of the tree.

In these cases, the only thing to do is wait and see. It is possible that in the spring, the buds that have already formed on the tips of those branches will still produce a new candle (the  growth from which new needles emerge). We encourage you to wait to prune until you are certain a branch has died, as cutting a branch that has a healthy bud on it will result in no growth next season. You can gently pinch the buds on damaged branches to find out if they’re still healthy – a firm bud is a healthy one, while a dried out dead bud will crumble between your finger tips. In this case, as with sun scald, the best treatment is a good deep watering 2 times a month through the winter when possible.

Come spring, even if no new growth emerges, if the remaining needles are still green, you’ve still got a healthy tree. Prune away the dead branches to expose the inner needles to light, give your tree a feeding with Jirdon Tree & Shrub fertilizer, and be sure to tell your tree how much it means to you and how happy you are that it’s still alive!