Deciduous trees are easy to tell from conifers or evergreens because deciduous trees lose their leaves in the winter. Deciduous trees surround us, providing crucial shade and cooling in the summer, but allowing us full access to whatever sun the skies offer us in the winter. Because they are so important to our ability to live comfortably throughout the year, it’s up to us to look out for their health and well-being. Luckily, there is a lot of information the color of a tree can provide about that tree’s health, and at Mr. Tree, we’re all about listening to what the trees are telling us.
In the growing season, healthy deciduous trees get all of the food they need through their leaves. When they’re feeling well, leaves should be dark green, large, and firmly attached to the branches. A healthy tree will produce new growth every spring and sometimes into summer (the leafing season). You can keep an eye on the new growth by measuring the distance between the current season’s buds and last year’s (previous buds will appear as scars on the branch). The amount of growth varies by species, but you can check online or with your local nursery or tree care provider to help get an idea of what you should expect.
During the leafing season, deciduous trees may indicate ill health when their leaves become spotty. For instance, a tree that has oak wilt will produce wilted leaves spotted with brown, starting at the top of the tree. This disease can be fatal to red oaks in particular. The leaves of deciduous trees turn lovely shades of yellow, red, and orange in the fall, but if the leaves of the tree are yellow in the growing season, that can be a sign of a serious problem.
It’s also a good idea to keep an eye out for lesions on otherwise green leaves. Anthracnose is a common disease among deciduous trees (especially sycamores, ashes, and oaks). It can cause dark, sunken bruises on leaves, stems, flowers, and fruits. Anthracnose doesn’t normally require treatment, but simple maintenance, such as regular pruning and increasing air circulation around the tree by removing fallen branches and twigs, can keep unsightly bruises off of the tree’s healthy green leaves.
Most deciduous trees have brown trunks. But it pays to look beneath the surface when it comes to deciphering information about a tree’s health. Using a pocket knife or a fingernail, you can look beneath the hard, outer layer of bark. Beneath that layer is the cambium layer. The cambium layer should look fresh, green, and moist. If the tree’s trunk is dark brown and dry all the way through, the tree may be seriously ill or even dead.
Dead trees can be extremely dangerous in any season. In the summer, they can catch fire or collapse in a storm. In the winter, the added weight of ice on the brittle, dry branches can cause them to break clean off, sending them crashing into cars, power lines, or even people. If you’ve found a dead tree, it’s important to have it removed.
Make sure, however, to check multiple areas of the tree to be sure that you haven’t just found an unhealthy spot on the trunk. Dead wood can exist on any tree, even ones that aren’t sick. The key to keeping the tree healthy if you’ve found dead wood is to adopt a regular pruning schedule. Pruning trees in the dormant season will help keep them healthy.
White leaves or white spots on the trunk are the easiest-to-spot signs that a tree isn’t feeling well. Powdery mildew can occur on the leaves and branches of trees that are living mostly in the shade, especially when it’s humid but not rainy. This fungus can cause anything between white spots on otherwise healthy-looking leaves to fully white foliage. The good news is that powdery mildew can be treated fairly easily with a fungicide.
Have you ever seen a tree that looks drought-stressed but is standing in sopping-wet earth? The leaves may be pale green or yellow, curling inward, and looking parched—no matter how moist the soil is beneath. This coloration can indicate root rot, a fungal disease that attacks trees planted in poorly drained areas. Prevention is the only treatment for root rot. The Pacific Northwest is soaking wet several months of the year, so we need to be especially aware of this potential concern.
Yellow leaves in leafing season can also be a sign of sickness. While we expect to see yellow in the fall, pale green or yellow leaves in the spring are signs of stress. If those same leaves are still clinging to the tree in winter, instead of falling to the ground like the others, the tree is telling you that it needs swift intervention.
Though red leaves are lovely to view in the fall, reddish areas on trunks or branches could be signs of a problem. Deciduous trees are susceptible to a variety of canker diseases like cytospora. Cankers appear as localized, sunken, discolored areas on the tree—most often reddish in coloration—and can be caused by animal exploration, mechanical injuries, or even passing environmental factors. Damage to the bark allows pathogens to seep in. Over time, if the canker grows, it can kill branches and, eventually, the whole tree. Trees with cankers need to be carefully pruned back with sterilized sheers to avoid spreading the disease.
At Mr. Tree, we know that trees can tell us a lot about their health with their leaves and bark. The color of a tree can tell you everything you need to know. Sometimes, the health of a tree is beyond our control. We can do our best, though, to make sure that the deciduous trees that surround us are happy and safe by pruning regularly, making sure that the trees are getting enough food and water, and keeping an eye on their colors to see if they’re trying to send us a message.