The ABCs of Growing ArborvitaesFrom the diminutive ‘Tiny Tim’ to the towering ‘Green Giant’, arborvitaes come in a diverse array of shapes and sizes. Here are some varieties to try, along with basic care and planting tips.
If you’re looking for a fast-growing, easy-care evergreen to use as a privacy screen or hedge, an arborvitae is hard to beat. Plant several of them in a row, and in just a year or two the lush, dense foliage will fill in to create the ideal living fence. But don’t overlook the many other ways you can use arborvitaes in both formal and informal garden designs. These versatile conifers are suitable for almost any purpose.
A trio of columnar arborvitae trees adds vertical interest to this garden scene. Photo by: Ottochka | Dreamstime.
Arborvitae (Thuja) is a genus of five species, but these two North American natives are the most common:
- Thuja occidentalis (American arborvitae or eastern arborvitae) - This arborvitae is a mainstay of many residential gardens because it’s widely available and has loads of cultivars to choose from. It prefers moist but well-drained soil and is very tolerant of cold climates. The foliage tends to darken to bronze in the winter, but some cultivars remain green all year.
- Thuja plicata (giant arborvitae or western red cedar) - Native to the Pacific Northwest, this fast-growing thuja can reach heights of 70 feet or more, although smaller cultivars are available if you prefer a shrub-sized plant. It grows best in coastal climates (zones 5-7) with cool summers and mild, wet winters but is adaptable to most soil conditions. It has a uniformly conical shape, spreading up to 20 feet at the base. The foliage has the added advantage of remaining green all year.
- Sometimes other genera are commonly called arborvitae as well, they include: Chamaecyparis, Thujopsis, and Platycladus.
The mature size of an arborvitae depends on the species and cultivar. Some low-growing shrubs are under 3 feet tall. Large trees can exceed heights of 70 feet and widths of 25 feet.
Mounded, conical, pyramidal, rounded, or pendulous, depending on the cultivar.
Most arborvitaes have flattened, lacy sprays of aromatic needles, with colors ranging from emerald green to gold. Clusters of rosebud-shaped cones measuring about ½ inch long appear in early summer, turning from green to nutmeg-brown at maturity. Female cones have 6-12 overlapping scales, male “cones” rather insignificant in most species.
The growth rate of arborvitae varies depending on the species and cultivar. Some are very fast growers adding 3 to 4 feet per year, while others, such as dwarfs and miniatures, grow much slower.
Don’t plant your arborvitae too deeply or it will languish and eventually die. Photo by: Radovan1 / Shutterstock.com.
When to plant:
You can plant an arborvitae at any time of year, but fall is typically the best season because the cooler temperatures prevent heat stress and the moisture from fall rains helps to establish a strong, healthy root system (see What to Plant in Your Fall Garden).
Where to plant:
- Plant your arborvitae in a spot that receives at least 6 hours of direct sunlight daily. Although some varieties can tolerate partial shade, growth will become sparse if they don’t receive enough light.
- Arborvitaes grow in most soil types, but they don’t like soggy feet. Plant only in well-drained soil, or add amendments to improve drainage if your soil contains a lot of sand or clay (see Garden Soil 101).
- Plant arborvitaes where they can spread their roots and have room to grow to their mature size. When planting a hedge or screen, leave at least 3 to 4 feet between plants. Staggering arborvitaes in a zig-zag pattern instead of cramming them into a tight row will look more natural and give them more space.
How to plant:
- When purchasing a potted or burlap-wrapped arborvitae at a nursery, plan on planting it in your garden within a few days after bringing it home so the roots don’t dry out.
- Dig a planting hole that is an inch less deep than the plant's root ball but two to three times as wide so the roots have room to expand.
- Place your arborvitae in the hole, making sure that the top of the root ball is higher than the surface of the soil so the roots don’t suffocate. Gently fill the hole with excavated soil, and water thoroughly to settle the soil. Do not pack the soil or tamp with feet.
- After planting, water the roots thoroughly by letting a hose drip at the plant base or by using a soaker hose. Repeat these deep soakings at least twice a week (if you don't receive rain) until the roots become established.
Planting in containers:
Smaller cultivars of arborvitae can be used as attractive container plants or topiaries that will provide season-long interest. Dwarf forms, in particular, are tolerant of some root restriction and can thrive outdoors in pots for years.
- Choose a suitable pot size (one a few inches larger than the size of the root ball) to give the roots ample growing room. Your pot can be made of clay, ceramic, concrete, fiberglass, treated wood, or sturdy plastic, but in colder climates use a material that is freeze-thaw resistant. Good drainage is a must.
- Partially fill the pot with a high-quality potting mix, preferably one specifically formulated for evergreens. Don’t use garden soil, which is too heavy and compact and will inhibit drainage.
- Place the root ball on top of the soil in the middle of the pot, and then add more soil until it reaches the top of the root ball. After planting, water the soil thoroughly and then lightly tap the surface to remove any air pockets.
- To help retain moisture, spread a layer of mulch or compost over the top of the container around the root ball.
Mulching around the base of your arborvitaes will help retain moisture in the soil. Photo by: Ozgur Coskun / Shutterstock.com.
When planted in good soil and given enough water and sunlight, an arborvitae rarely needs a dose of fertilizer to stay healthy. However, if new growth becomes sparse or your soil is less than ideal, you may need to give your plant a nutritional boost. (See these recommendations for fertilizing evergreens from the University of Minnesota Extension.) If you are growing arborvitaes in containers, you will need to fertilize them regularly to replace nutrients that leach out of the soil. Use a slow-release granular fertilizer to avoid root burn, and be sure to water well before and after each application.
Watering and mulch:
Arborvitaes can suffer stress from both underwatering and overwatering. If your plant isn’t getting enough water, the foliage will start to yellow or brown and the needles may drop. (In fall, some browning and needle drop is normal.) Overwatering may also cause needle discoloration and could lead to irreversible damage caused by root rot and fungal infection.
As a general rule of thumb, give newly planted shrubs about an inch of water a week during the growing season, keeping the soil evenly moist but not saturated. You can decrease the frequency of watering as the roots become established. Use a hose to deliver water directly to the root zone. To keep the soil moist, place a layer of compost or mulch around the base of the plant (avoid covering the trunk or crown of the plant) and replenish it annually. As the mulch decomposes, it will also improve the soil structure. Learn more about the right mulch to use and the best methods of application.
Potted arborvitaes should be watered regularly, even during the winter months. Because evergreens don't go completely dormant in winter, they will still need moisture.
Heavy snow and ice buildup can bend and break the branches of taller arborvitaes. Use a broom to gently brush off heavy, wet snow before it has a chance to accumulate. Some types of arborvitae, especially those that put out two or more leaders, may need to be staked to keep them in an upright position. Storm-damaged arborvitaes can often be rejuvenated by pulling the drooping branches upright with ties and pruning off broken limbs. See these winter care tips from the University of Illinois Extension.
Diseases and pests:
One reason why arborvitaes are so popular is because they are rarely troubled by insect and disease problems. However, they may succumb to needle and twig blight caused by fungal attack, especially if air circulation is inhibited by crowding plants too closely together. To control blight, prune off all affected branches and treat with a fungicide. Also watch out for bagworms, which like to feed on the foliage of arborvitaes and other evergreens. The best control method is to handpick the spindle-shaped egg bags (which are actually made from the needles of their host plants) and destroy them before the larvae hatch and begin feasting on the branches. Spidermites and stem canker can also be problems.
What about deer?
The soft, tender needles of American arborvitae (T. occidentalis) are a delicacy for foraging deer. Unfortunately, the needles won’t grow back once the branches are stripped bare. If deer are a problem in your garden, you’re better off growing giant arborvitae (T. plicata), which deer find less appealing, or a different deer-resistant evergreen such as juniper. Learn more about the best deer-resistant plants for your garden.
Arborvitaes will retain their natural shape as they mature and regular pruning is usually not necessary. Arborvitaes will tolerate more frequent and heavier pruning if you want to shape them into formal hedges and topiaries. Follow these dos and don’ts to get the best results:
- Do give arborvitaes a light pruning in early spring to keep them tidy and encourage thicker growth. Because new growth only develops from the leafy part of a branch, don’t cut back to bare wood.
- Don’t lop off the top of an arborvitae to reduce its height. No new growth will occur once the branch tips have been sheared away, and you’ll end up with a permanent buzz cut. Instead, use selective pruning or thinning cuts to lower the height.
- Do maintain the natural shape of your arborvitae and keep it wider at the bottom than the top. If you prune it into a V shape, you will shade the lower branches and the foliage may die back or become sparse.
- Do remove dead or diseased branches immediately to prevent decay and allow new growth to fill in the gaps, pruning them off at the point where they leave the trunk.
- Do remove accumulated dead foliage inside the plant annually or more frequently to improve air circulation and reduce chance of disease.
Here are some additional tips from The Morton Arboretum on the best methods for pruning arborvitaes and other evergreens.
USING ARBORVITAE IN THE GARDEN
Here are some design ideas for incorporating arborvitaes into your garden:
- Add instant sophistication to an entryway by placing a matching pair of arborvitaes on either side of your front door.
- Create evergreen focal points in the garden by intermixing arborvitaes with your perennials.
- Use larger arborvitaes as statuesque specimen trees, or plant smaller cultivars in decorative pots and sculpt them into eye-catching topiaries.
THUJA OCCIDENTALIS ‘DEGROOT’S SPIRE’
A slow-growing cultivar with a very slender, upright habit, reaching a height of about 20 feet but width of only 4 to 5 feet. The mossy-green foliage bronzes slightly in winter. Although densely branched, the narrow form may make it susceptible to breakage from ice and snow accumulation. Staking after planting will help to prevent damage.
Suggested uses: Formal hedge, topiary, or accent plant by an entryway.
THUJA OCCIDENTALIS ‘GOLDEN GLOBE’
This bright little orb of gold is a great choice for providing winter interest and mixing with other shrubs to add contrast. It maintains a natural rounded shape, growing up to 3-4 feet tall and wide at maturity.
Suggested uses: Short hedge, foundation plant, or edging shrub along a walkway.
THUJA ‘GREEN GIANT’
This stately pyramid-shaped arborvitae (a hybrid of T. plicata and T. standishii, a Japanese species) is one of the fastest growing, adding 3 feet or more to its stature each year before attaining a mature height of 50 to 60 feet. Sturdy and adaptable, it grows in sandy loam or clay soils and resists the weight of heavy ice and snow. The foliage remains a glossy dark green in all seasons.
Suggested uses: Tall hedge, specimen tree, or natural windbreak
THUJA OCCIDENTALIS ‘HETZ MIDGET’
Shaped like a pin cushion, this charming dwarf variety has small sprays of lacy blue-green foliage that turn bronze over winter. Extremely slow-growing and hardy, it remains a midget-sized 3 to 4 feet.
Suggested uses: Rock gardens, container plant, or foundation shrub.
THUJA OCCIDENTALIS ‘RHEINGOLD’
One of the best for year-round color, with bright yellow foliage in summer that turns a deep golden copper over winter. Another attractive feature is the compact domed shape, which tops out at a height of 3 to 5 feet.
Suggested uses: Container plant, garden accent, or border shrub.
THUJA PLICATA ‘WHIPCORD’
This sassy little thuja looks like a green rag mop, with twisted yarn-like foliage that shoots up from the center before cascading downward on arching branches. Grows 4 to 5 feet tall with an equal spread.
Suggested uses: Focal point for a small garden.
THUJA PLICATA ‘ZEBRINA’
This stunning arborvitae is aptly named for its two-toned foliage with golden yellow accents. It has a narrow pyramidal shape, reaching a height of 30 feet or more and a width of 8 to 12 feet at the base. Like ‘Green Giant’, it has a fast growth rate, averaging about a foot per year.
Suggested uses: Vertical landscape accent, tall hedge, or privacy screen.
THUJA OCCIDENTALIS ‘SMARAGD’
German for “emerald,” ‘Smaragd’ has glossy bright-green foliage that maintains its color in all seasons. Reaching an ultimate height of 10 to 15 feet and spread of 3 to 4 feet, it stays narrow and compact with minimal pruning. Hardy and cold tolerant (down to zone 2).
Suggested uses: Privacy screen, formal hedge, or topiary.
THUJA OCCIDENTALIS ‘TINY TIM’
This is one of the smallest and slowest growing thujas, developing into a little green mound about a foot tall and wide after 10 years. Features delicate, finely-branched foliage that turns bronze in the winter.
Suggested uses: Container plant, bonsai specimen, borders, or edging.