Tree care is a critical investment for the future of your landscape. A healthy tree may occasionally have brown leaves, dead limbs, and other common problems, but sometimes it means you have a dying tree. It's important to take notice of such troubling signs and learn their causes so you can try to address the issue. In many cases, the causes are specific to the type of tree.
Over-Exposure to Sun
Brown leaves are often related to over-exposure to the sun, commonly known as "leaf scorch." This can be aggravated by problems such as lack of water, too much fertilizer, damage to roots, and exposure to strong wind, all of which can stress the tree and leave it vulnerable to the sun. Young trees are especially susceptible to sun overexposure, so it's advisable to plant them in the spring or fall when UV rays are less intense.
Transplanting the tree to a location with less sun or providing a shade screen or reflector can help to treat sun over-exposure. In some cases, cheesecloth can be applied to the tree's branches to add a layer of protection.
Brown leaves appearing on trees in spring can indicate frost damage. This can ruin the tree's appearance temporarily, but it's unlikely to kill the tree. If browning appears in summer, inadequate watering or high winds may be the cause. Leaves with black spots are likely caused by a fungus that thrives in moist conditions, making this a common problem in humid climates.
Magnolia trees are often susceptible to frost damage, especially if they're young. If you think your tree may be bothered by freezing temperatures, you can wrap it in burlap or an old sheet to protect it during the coldest months.
Trees that have recently been transplanted often experience a difficult period of transplant shock, leading to a host of potential problems, including leaf wilt, leaf scorch, yellowing leaves, and leaf rolling or curling. Don't assume you need to water a tree more just because it has brown leaves when its foliage would normally be green.
Don't worry if your tree is experiencing transplant shock, as most often it will be overcome with time. Usually, if you consistently give it the right amount of water, the tree will begin to thrive when it starts to take root. To help prevent transplant shock, let the tree acclimate to its new home for several days before placing it into the ground. Also, make sure the planting hole is at least two to three times larger than the root spread and deep enough to allow more space for growth.
In the case of Bradford pear trees, leaves may turn black (not yellow or brown) after transplanting. The culprit may also be fire blight disease, so-called because it causes tree parts to look as if they've been burned. If you do suspect you have an issue with this disease, an arborist can treat the bacteria with a specialized spray and remove infected branches.
Insects and Disease
When treating your tree for insects or disease, it's important to confirm exactly what the issue is before taking action. Once you've targeted the condition, most often there is a type of spray that will aid in eradicating the insects or disease.
Emerald cedar, or 'Emerald Green' arborvitae, commonly develops brown leaves in summer. This can be due to several factors, including insects, diseases, and even dog urine. Of course, the problem also can be simply due to drought. Brown leaves on the inner part of Emerald cedars are normal during fall and spring, but leaves turning brown at the outer tips of branches can indicate serious problems.
Many trees need a significant amount of watering, especially if they're young or newly transplanted. During the first few months, a daily watering with a hose is necessary for many types of trees if you don't have an irrigation system in place. If your area is experiencing a particularly dry season, more established trees will also require watering to maintain their health.
It's possible to give too much water to a tree, so be on the lookout for yellowing or drooping leaves that indicate overhydration, as opposed to dry, brown leaves that are a result of lack of water. If you think you may have over-watered your tree, take a break from daily watering until the leaves start to perk up and the surrounding soil has dried.
If a tree is planted in compacted soil or clay, the lack of space for the roots to expand makes it difficult for the tree to thrive. Before planting, make sure the ground is loamy and well-drained, and that the soil has been loosened in order for the tree to take root with ease. You can mix in organic material like mulch into the clay or compacted soil to make it more inhabitable for a tree, but this may be difficult to do without the help of a rototiller or excavator.
Fertilizer can provide a boost of nutrients and help a tree thrive, but too much of this tree food can actually cause harm. Over-fertilizing can burn your tree's roots or foliage, and in some extreme cases, the tree may die. It's important that you make sure the fertilizer you use is compatible with your tree, that you're applying the correct ratios, and that the feedings are spaced out over the suggested amount of time.
If you believe your tree is experiencing the effects of over-fertilization, trim back overtreated branches and flush the surrounding soil with water. You can also protect the root base with a layer of mulch, flushing once more with another round of water after application. Repeat the watering process as necessary, making sure to give enough breaks to prevent overhydration.