Arborvitae trees are also known as thuja, which is a genus consisting of five species of coniferous trees in the Cupressaceae (cypress) family. There is some confusion regarding arborvitae, as they are often simply referred to as "cedar trees" but aren't actually true cedars.
They look like other true cedars in some ways and offer a lovely aromatic scent that makes one think of cedar and lemons. These trees are known for their vibrant green color that only deepens as they age.
Arborvitae translates to "tree of life" in Latin, and many parts of the tree have been used in traditional medicine to help stave off scurvy and other common ailments like upper respiratory infections.
The following article contains some common issues that these trees may suffer from, as well as some remedies to help save a dying arborvitae tree.
The two most common species of arborvitae in the U.S. are thuja occidentalis and thuja plicata, both of which are sold as, or referred to as, cedar trees. They are not considered true cedars, however, which consist of species in the cedrus genus in the family Pinaceae (pine).
Thuja plicata is commonly called western arborvitae, western red cedar, or giant arborvitae since it grows 70-feet or more very quickly. These trees are native to the pacific northwest and hardy to zones 5-7. While called "cedars," they aren't usually planted in residential landscapes because of their size, and are more common in forests.
Thuja occidentalis is native to mainly northern and eastern states and is used regularly as an ornamental tree in residential yards. It's a smaller tree that's easy to care for, drought-tolerant, and cold-hardy, making it a popular choice among various landscapes.
The other three species that are called arborvitae include: chamaecyparis, thujopsis, and platycladus, but for the purpose of this article, we will focus on the most popular residential arborvitae tree: thuja occidentalis.
Thuja occidentalis is also known by many names, such as eastern white cedar, northern white cedar, smaragd cedar, or American arborvitae, and is mainly sold commercially as "emerald green" cedar.
This species is popularly used in residential yards, and easily found in garden centers and nurseries. Its decorative evergreen foliage grows up to 20-feet tall in upright, conical fashion along a single trunk with brownish-red bark.
They are easy-to-care-for trees that provide excellent privacy, often being used as hedges and living fences, or added amongst landscapes that need some winter interest.
Although they can withstand various cold and hot temperatures from zones 2-7, and rarely have problems with disease or pests, sometimes arborvitae can experience certain forms of environmental stress that may quickly result in the death of the tree.
Find the Cause
The first step in saving your arborvitae is knowing the signs that it's in distress. The main tell-tale is brown, brittle leaves, bald areas, or weakened branches.
If you spot your cedar tree showing any of these symptoms, it's important to take action as soon as possible, as it's usually something to do with its environment that can be changed or rectified.
The faster you can determine what's causing it to suffer, the sooner you can work on resuscitating your tree. While there are some temporary ways to treat symptoms of a dying arborvitae, it's important that you find the proper solution for the problem to ensure long-term longevity.
The most common sign of thuja distress is the browning of foliage. There are many different reasons why this can happen, so it depends on specific things like how and when it was planted, the planting site, soil conditions, and climate.
While cedar trees are drought-tolerant once established, the most common reason they die is because they were not watered well enough in the first year of being planted.
Planting in the spring or fall can help with this as there's naturally more rainfall in most areas, and the weather is cooler. If you do plant in the summer, it's especially important to water the tree deeply every few days in times of extreme heat.
Thuja loves full sun, but intense heat can quickly damage a newly planted tree that's trying to establish roots and hasn't received enough water. The best way to water is to soak directly into the soil for about one hour in the early morning or evening to avoid the hot afternoon sun.
The other problem that plagues newly planted trees is the site choice. While emerald cedars aren't extremely picky about soil types, they'll survive much better if they aren't planted in heavily compacted soil that restricts new roots.
Adding some compost or organic material to the planting site can increase the chances of your arborvitae tree thriving within its first year. However, you don't want to overdo it either, as the tree needs to learn to send roots out to find nutrients.
While fertilizing isn't always essential, a nitrogen-heavy feeder of 30-10-10 can give them a boost in nutrient-depleted soils during the growing season from spring to early summer. Stop fertilizing later in summer, but continue to water deeply in periods of extreme heat and drought to prepare it for winter dormancy.
The other consideration for your planting site is to establish whether your tree will experience any harsh winds or desert-like heat. Cold weather can cause desiccation (the drying out of roots), but relentless winds or hot sun can also put undo stress on arborvitae, which prefer moderate conditions.
Don't plant single trees in wide open spaces that receive this kind of extreme weather, and consider planting many beside each other to help protect themselves from harsh winds and heat.
Mites and aphids can be a problem for arborvitae but are thankfully fairly easy to take care of. Mites are tiny anthropods that spin their webs over foliage and suck out nutrients from the tree. You can identify them through light webbing and consequent leaf discoloration.
Aphids are slightly larger than mites and can be identified by the naked eye. They're often found gathered in large numbers on the undersides of foliage or along stems, where they also draw out the plant's juices.
Both of these pests can be eradicated by strong blasts with a hose, as the water will clear away webs and kill any of the soft-bodied creatures. Aphids will not usually come back after being sprayed off of a plant, but an extra step is to spray the tree with insecticidal soap.
This type of insecticide is safe for most plants and animals but can harm beneficial insects like bees, butterflies, and other insects that eat aphids like ladybugs, so try the blast with the hose first, and then check a few days later to see if there are any pests left.
You can also place other plants that naturally repel pests in your yard near your arborvitae. Spider mites and aphids are both repelled by anything in the allium genus like onions, garlic, chives, and leeks. Marigolds and common aromatic herbs like basil, mint, rosemary, dill, etcetera, will also deter them.
These pests are more worrisome for arborvitae trees, as thuja is their main food source. Leafminers are tiny, whitish-gray moths whose larvae mine into and feed off of foliage.
You can identify this problem somewhat easily as the tips of foliage are often first to discolor around midsummer when feeding begins. By fall, most of the damage is done, so it's best to eradicate the problem before it gets out of hand.
In the forest, leafminers are naturally kept in check by bird populations and wasp parasites, but this isn't always the case with affected specimen trees in residential yards.
Thankfully, the damage from leafminers is mainly aesthetic and not likely to kill the tree. Pruning affected foliage once the problem is spotted is the best way to prevent further damage and keep the arborvitae tree looking healthy.
Depending on where you live, certain animals will be considered pests to your arborvitae tree because they like to snack on the tasty foliage.
Deer, moose, rabbits, and even porcupines will dine on their nutritious leaves, but white-tailed deer are the most notorious grazer and will over-browse, causing damage to the trees if there isn't enough supply.
Though there are repellents for animals, they are not usually effective and can harm both the animals and your plants.
The best way to prevent animals from feasting on your arborvitae is by putting up some sort of barrier. Netting can easily be placed around the plants and trees, or you can fence in your entire yard.
There are a few different cultivars of the thuja tree, and the "Green Giant" variety is not only an extremely fast grower (3-6 feet per year!), it's also been bred to be deer-resistant.
Winter Cold Damage
Thuja occidentalis is a cold-hardy arborvitae and is therefore used to freezing temps. Sudden or extreme fluctuations in temperature can affect your thuja tree, however, especially if it happens before the tree has prepared for dormancy.
If the tree hasn't had time to properly adjust to the cold snap, it can potentially kill the tree or cause it to look sickly. If you know the weather is about to change drastically, consider covering the tree, especially if it's not in a protected area among other trees and shrubs.
Mulch can also protect your arborvitae tree and help it retain moisture. Trees that are well-watered will have the best chance of withstanding any flash freeze, so watering deeply before a deep freeze is another good tactic for prevention.
Older trees are more susceptible to harsh weather, but newly planted trees are, as well. Prune off any damaged or broken branches and foliage to help it recover.
Ways to Prevent Emerald Cedar Damage
While there are some things that will cause damage to your arborvitae, these trees are usually fairly resistant to most threats as long as they are planted in the right conditions.
Choose a location with full sun and well-draining soil that gets a good amount of rainfall. They are not picky about soil, but would lean towards an alkaline pH level versus acidic if given the choice.
They can handle part shade and would prefer that to being exposed to extremely hot, desert-like conditions. They will not tolerate full shade, so location is a very important part of ensuring your arborvitae's vitality.
Keep a regular watering schedule, especially in the first year of planting. Water twice a week during the first growing season, and water deeply so that it gets about an inch of water each time. After its first year, make sure it gets half an inch of water each week.
Apply around 1-3 inches of mulch around the tree, but avoid laying it close to the trunk. Organic material is an excellent choice as mulch, or consider native groundcovers that prefer similar conditions.
How To Plant Emerald Cedar
As mentioned, arborvitae trees will have the best success if they are planted in the fall or early spring. Any time the temps are moderate, and lots of rainfall is expected in the forecast is an ideal time to transplant.
If you are planting a privacy hedge of emerald cedars, make sure to leave enough space so that the trees can mature into their full size without being too crowded, but also not too much space between them.
Emerald cedars are sold in various sizes and points of maturity, so spacing depends on their size at planting. If they are 3-4 feet in height, keep in mind that they will grow another 15 feet tall and also a few feet in width. Leave approximately 3-4 feet between young trees to ensure that they have enough space to fully mature.
You can also find emerald cedars that are 10-12 feet tall, which means you won't need to leave as much space between them. These will cost you more upfront but will also give you privacy right away. Large trees will need just as much attention during the first growing season as smaller trees.
Follow the instructions on the plant tag on how deep to dig your planting hole, and keep the back-fill soil you dug out to fill back in once the tree is planted.
It's important to be picky when choosing an arborvitae tree for your yard or landscape. The best time to purchase emerald green cedar trees from the garden center is in the spring or fall when the trees are fresh and well-cared for.
As the growing season progresses, often these trees are often neglected and left in hot areas where they don't receive enough supplemental water. Large trees in small containers become root-bound, and roots start to suffer. You may see them extending out of the container in a desperate plea for water and nutrients.
Smaller trees may fare better, as they don't need as much water, but don't purchase any arborvitae that has brown foliage or exposed roots: these are, sadly, trees that likely won't make it past their first year of planting.
Keep in mind, as well, that garden centers will get fresh stock to replace older trees, so if you don't see any that are thriving, ask when they are expecting another shipment. You may get a deal on distressed trees, but chances are these trees won't survive.
Once you have chosen your emerald green arborvitae trees, plant them as soon as possible. The less time they spend in their small containers, the better chance they have of rooting successfully.
Though many things can affect your arborvitae tree, there are several things you can do to save a dying arborvitae tree. The easiest way to prevent an arborvitae's death is to plant it properly in the first place.
Once in the ground, stay alert and observe how it's doing so you can make quick adjustments as needed. Fast action and proper site conditions will ensure your beautiful, healthy arborvitae tree stays that way.