Questions Answered Series: Arborvitae (Thuja)
Your Questions on Arborvitae, Answered!
If you’re looking to add structure, privacy, and lush green foliage to your garden, then arborvitae (or Thuja) is probably the shrub for you. They can be short, tall, rounded, pyramidal, green, or blue, which means there really is an arborvitae for every garden. Whether you’ve already planted arborvitae or are planning to buy some soon, you can find the answers to all your questions here. See what others are asking and learn how to grow arborvitae like a pro.
- What are the different types of arborvitae?
- How do you grow arborvitae?
- How far apart should I plant my arborvitaes?
- Can arborvitae grow in the shade?
- How fast does arborvitae grow?
- How much should I water my arborvitaes?
- Why is my arborvitae turning brown?
- When is the best time to plant arborvitae?
- Should I trim my arborvitae? If so, when?
- Are arborvitaes evergreen?
- How do you straighten a bent arborvitae?
- Does arborvitae have a lifespan?
- Arborvitae, juniper, or false cypress: what’s the difference?
- Why are my arborvitae’s branches drooping?
- Will arborvitae grow in containers?
- Is arborvitae deer resistant?
- Is arborvitae toxic to dogs and cats?
- Which arborvitae grows the fastest?
- Why is my arborvitae turning yellow?
- Are arborvitaes native?
- Should I wrap my arborvitae in winter?
- Are arborvitae roots aggressive or invasive?
- Can I overwater my arborvitae?
What are the different types of arborvitae?
Is it a shrub? Is it a tree? How big does arborvitae get? Sometimes, it’s hard to tell when it comes to arborvitae (Thuja). There’s so much variation in size among the different arbs we offer, ranging from 1 foot to over 50 feet tall! We use the terms shrub and tree interchangeably for our arbs, but, botanically speaking, they’re all shrubs from their low branching at the base.
The genus Thuja comprises five species, including two natives that we offer: Thuja occidentalis and Thuja plicata. The main difference between the two is their size and hardiness. T. occidentalis (or eastern arborvitae) is cold hardy down to zone 3, boasting evergreen foliage that may turn bronze in winter. T. plicata (giant arborvitae or western red cedar) is from the west coast, so it prefers mild winters in zones 5-8. Their foliage stays green all winter long (no bronze coloration), which is an advantage of the species. But their green foliage comes with a massive habit. Most T. plicata reach over 30-50 feet tall (except the dwarf Fluffy®).
Does this answer your question? Probably not. So here’s a diagram showing the difference in size and shape for each arborvitae we offer. This is the most helpful tool for envisioning which cultivar belongs in your garden.
How do you grow arborvitae?
Soil: Best grown in moist, fertile, well-drained soils. Poorly drained and wet sites should be avoided.
Light: Full sun (6+ hrs direct sun) to part sun (4-6 hours direct sun)
Water: Keep the soil moist but not wet.
Fertilizing: Top dress in spring with a slow-release, balanced fertilizer.
Winterizing: Consider applying a thick mulch around the root zone in winter to protect it in exposed locations or colder zones. Tolerates wind once established and withstands heavy ice or snow. They may darken or bronze slightly in the winter.
Maintenance & Pruning: Requires little or no pruning but can be sheared easily if necessary. Avoid pruning in late summer or fall as pruning stimulates new growth, which can be easily damaged by fall and winter temperatures.
How far apart should I plant my arborvitaes?
The distance between each plant at planting all depends on the size of your arborvitae, which varies significantly among cultivars. The general rule of thumb is to space them based on their width. For example, our Full Speed A Hedge®’ American Pillar’ arborvitae reach 5 feet wide, so you should plant them with their centers 5 feet apart.
However, if you’re looking for a lush privacy hedge that fills in fast, you can plant them even closer. The minimum spacing should be the plant width divided in half. Therefore, if you want a dense Full Speed A Hedge®’ American Pillar’ hedge, you can plant them with their centers 2.5 feet apart. If you’re growing a hedge of arborvitae, the minimum spacing is definitely recommended.
Can arborvitae grow in the shade?
Unfortunately, arborvitaes are not suited for shade. They grow best in full sun (6+ hours direct sunlight) to part sun (4-6 hours direct sunlight), requiring at least 4 hours of sun for lush greenery. Gardeners in warm climates should grow them in part sun, where they'll get some shade in the afternoons. However, when grown in too much shade, they'll look spindly and sparse.
An alternative to arborvitae in shade gardens would be yews or boxwoods.
How fast does arborvitae grow?
Two things determine the growth rate of your arborvitae: the cultivar and the growing conditions. Tater Tot® won’t grow quite as fast as ‘Green Giant,’ and even two ‘Green Giant’ arborvitaes can grow at much different rates if they are not grown in areas with optimal light, water, and temperature.
In general, we say it takes 5-9 years for shrubs to reach maturity. It may be shorter for smaller cultivars or even longer for larger ones. Nevertheless, we do offer growth rates under optimal conditions for our four most common arborvitaes:
- Full Speed A Hedge ‘American Pillar’: up to 2 feet a year
- ‘Green Giant’: up to 3 feet a year
- ‘Emerald Green’ (or ‘Smaragd’): up to 18 inches a year
- ‘Hetz Wintergreen’: up to 2 feet a year
How much should I water my arborvitaes?
This is always a tricky question to answer, as it relies heavily on the growing conditions in your garden! Arborvitaes like moist, well-draining soils, and how much water you use to keep the soil moist depends on your soil type, sunlight, and climate. In general, we recommend watering 1 inch a week. Feel the soil with your fingers (at least a few inches deep) to better understand your soil’s moisture level between waterings. Does it feel dry? Water them a little more. Does it feel wet or soggy? Use less water to avoid drowning them. Also, keep an eye out for browning or yellowing leaves, as this might be caused by under or overwatering.
Why is my arborvitae turning brown?
It can always be worrisome when plants turn brown, especially when they should be evergreen. There are a few reasons why this may be happening:
- Drought stress: brown foliage is usually a sign of drought stress. Though many arborvitaes can handle mild drought once established, they prefer to grow in moist yet well-draining soils. The easy solution is to water more frequently.
- Transplant shock: if branches of your arborvitae turn brown right after planting, it’s likely just transplant shock. Planting can be stressful for the roots as they adjust to a new garden, so it’s not uncommon for a few branches to die. It’s okay; your shrubs will still bounce back. Keep them well-watered (but not overwatered) as they establish in your garden.
- Natural foliage drop: if the foliage on the inner part of your arborvitae is browning, don’t worry! This is entirely normal and expected. As your arborvitae grows, the inner foliage will be shaded by new growth, causing it to turn brown and shed. It’s not being used for photosynthesis, so your plant no longer needs it.
- Winter burn: if you notice browning during or after winter, usually only on one side of your shrub, it’s likely winter burn. Sunlight and cold winds in the winter can dry out the foliage, turning it brown. Plant your arborvitaes in a sheltered location or protect them with tree wrap/burlap to avoid winter burn.
- Disease: Some fungal infections can turn your arborvitaes brown. Arborvitaes are more susceptible to disease when they are stressed, so water and fertilize them properly. Remove infected branches and treat your plant with a fungicide.
It’s fairly normal if your arborvitaes turn a little orange, purple, or bronze (not brown) in winter. As you drive around, you may notice it happening in other conifers as well. However, this should be temporary for the winter before turning green again in spring.
When is the best time to plant arborvitae?
The best time to plant arborvitae depends on where you live. For gardeners in cold climates, we recommend planting your arborvitae in late spring. It gives your plants plenty of time to establish before the next winter arrives. However, for gardeners in warm climates, we recommend the opposite. Instead, plant your arborvitaes in the fall to give them enough time to establish before the following summer.
With that being said, you can get away with planting your arborvitae in both seasons, no matter where you live. Ensure you provide plenty of water for the first few weeks after planting.
Should I trim my arborvitae? If so, when?
Arborvitaes are low maintenance, requiring no trimming or pruning for lush green growth. However, you can lightly trim them in early spring to remove winter dieback or gently shape them. However, we don’t recommend any heavy trimming or cutting them down to size. Rather than trimming your arborvitae to keep it small, we suggest choosing a cultivar that has a compact habit.
Are arborvitaes evergreen?
Yes, arborvitaes are evergreen, keeping their scale-like foliage over the winter for added interest. While most will keep their green color, especially in mild zones, it’s not uncommon for some cultivars to take on orange, purple, or bronze hues during the winter months in cold climates. This coloration is temporary for the winter!
Arborvitae, juniper, or false cypress: what's the difference?
Arborvitae, juniper, and false cypress are all members of the cypress family. However, though they’re related (and frequently confused), there a quite a few differences between them.
Compared to arborvitae, junipers (Juniperus) tend to have more bluish-green foliage, are slower growing, and produce aromatic “berries” that attract birds. While they take longer to grow, they are deer resistant, drought-tolerant, and easier to grow.
False cypress (Chamaecyparis) looks similar to arborvitae but comes in a broader range of textures and colors (like gold and blue). They tend to be smaller and much slower growing, but that might be good, depending on your garden. False cypress is also deer resistant, unlike arborvitae.
Why are my arborvitae's branches drooping?
If your arborvitae branches are drooping in the winter, it’s likely due to dry soil, heavy snow, strong winds, or all of the above. There are a few things you can do to prevent this.
- Apply a thick layer of mulch around the base of your plants to insulate the roots and keep the soil moist. If your plant dries out, it will droop and turn brown.
- Gently knock heavy snow off the branches of your plants.
- Plant your arborvitae in an area protected from strong winds (like on the side of your home or shed).
- Wrap your plants with burlap or tree wrap for winter protection.
Will arborvitae grow in containers?
Arborvitae grows well in containers, especially the dwarf varieties like Tater Tot®, Anna's Magic Ball®, and Fluffy®. There are three things to consider when growing arborvitae in pots:
- Select the right size pots for your arborvitae! We recommend starting small, then upsizing your pot as your plant grows. Keep in mind, many arborvitaes reach epic proportions, requiring very large containers. As they mature, you may have to transplant them in the garden.
- Make sure your container has large drainage holes. Arborvitae is not tolerant of saturated soils.
- Place your pot in an area that receives full sun (6+ hours direct sunlight) or part sun (4-6 hours direct sun).
We don't recommend growing our largest arborvitaes, like 'Green Giant' and Spring Grove®, in containers for longer than one or two seasons. They grow very quickly, requiring enough space to spread out.
Is arborvitae deer resistant?
With fragrant, scale-like foliage, you’d think arborvitae would be deer resistant. But – unfortunately – that is NOT the case. Rutgers University gives arborvitae a D-rating on their deer resistance list, which means they are “frequently severely damaged.”
If deer are a problem in your garden, we recommend planting tall junipers, false cypress, or boxwood instead.
Is arborvitae toxic to dogs and cats?
Arborvitae can be poisonous for cats and dogs when ingested in high quantities. Eating it can cause nausea, vomiting, indigestion, and death (though highly unlikely).
Which arborvitae grows the fastest?
Without a doubt, the two arborvitaes that grow the fastest are ‘Green Giant’ and Full Speed A Hedge® ‘American Pillar’. Both of these arborvitaes may start small but grow quickly to hide any unsightly views. ‘Green Giant’ can grow up to 3 feet a year, while Full Speed A Hedge®’ American Pillar’ grows 2 feet a year.
Why is my arborvitae turning yellow?
There are a few reasons why your arborvitae may be turning yellow:
- Overwatering: the most common cause of yellowing foliage is too much water. Arborvitae is not tolerant of wet soils and requires good drainage. If the roots stay wet for too long, they will rot, turning the foliage yellow.
- Nutrient deficiency: yellowing foliage is one sign that your plant is deficient in nitrogen, potassium, or iron. If you haven’t fertilized your arborvitae, now is the time to start! Apply a well-balanced slow-release fertilizer in early spring.
- Natural foliage drop: it’s entirely normal for the inner part of your arborvitae to turn yellow as it grows. The inner leaves are shaded by new growth, so the plant no longer needs them.
Are arborvitaes native?
All arborvitaes offered at Great Garden Plants are either American arborvitae (Thuja occidentalis), giant arborvitae (Thuja plicata), or a hybrid (Thuja x). All of them are native to North America!
Should I wrap my arborvitae in winter?
The short answer: it depends! Gardeners wrap their arborvitae in winter to avoid winter burn, which happens when the foliage dries out and dies from sun and wind exposure. Young arborvitaes planted in open areas in colder climates are most likely to suffer from winter burns. If this sounds like your plant, you might consider loosely wrapping it with tree wrap or burlap!
With that being said, not every arborvitae is susceptible to winter burn. If your arborvitae is in a sheltered location (protected from winds), has a mature root system (to access deep water reserves), or your area has mild winters (zones 7 & up), it will probably be fine without added protection.
Are arborvitae roots aggressive or invasive?
Thankfully, no! With a plant that gets this big, you'd think it has a monstrous root system to go along with it. Instead, it's mainly composed of shallow and thin fibrous roots that only spread as far as the aboveground width.
How do you straighten a bent arborvitae?
If you have a young arborvitae that is slightly bent, do not fear, as this can be set back into place! Just grab a stake, place it upright along the bent limb, and position it until it begins to stand upright on its own. While arborvitaes can withstand harsh weather conditions, young trees are susceptible to bending from heavy snowfall. Therefore, gently clean off your trees after the snowfall with a broom to keep your arborvitaes upright.
Does arborvitae have a lifespan?
According to the University of Washington Botanic Gardens, arborvitae, or Thuja occidentalis, has an estimated 50 to 150 years lifespan. The lifespan depends on species as well as environmental conditions.
Can I overwater my arborvitae?
Yes, you can overwater your arborvitae tree. While arborvitae needs moist soil to thrive, overly watered or waterlogged soil may lead to root rot and discolored leaves. Added layers of mulch can help maintain healthy levels soil moisture.
Written by: Miranda Niemic, click here to read bio.
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