Questions Answered Series: Arborvitae (Thuja) (2024)

• May 15, 2023

• 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?

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.

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.

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.

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:

1. Full Speed A Hedge ‘American Pillar’: up to 2 feet a year
2. ‘Green Giant’: up to 3 feet a year
3. ‘Emerald Green’ (or ‘Smaragd’): up to 18 inches a year
4. ‘Hetz Wintergreen’: up to 2 feet a year

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.

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.

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.

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.

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.

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.

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.

Written by: Miranda Niemiec, click here to read bio.

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