Thuja Occidentalis ‘Smaragd’ Growth Rate


Smaragd arborvitae is a semi-dwarf shrub. What growth rate can you expect from it?
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The emerald green arborvitae, or thuja occidentalis ‘Smaragd, is a semi-dwarf shrub with a compact, narrow, upright habit with tall sprays of glossy, brilliant green leaves that show small bundles of reddish-brown cones. It makes a lovely foundation plant and is sometimes planted by itself as a specimen plant in a landscape. Its slow development rate has not prevented it from becoming a very popular plant.

In this article, we will discuss the growth rate of thuja occidentalis ‘Smaragd’ and how we can speed up the process. 

How Fast Do They Grow?

The average height of emerald green arborvitae after one year is around 9 inches. When it first starts growing, its average annual growth rate will be between 12 and 18 inches. When the shrub is well-established, it will gradually slow its growth rate to anywhere between 6 and 9 inches each year.

a person planting a young thuja in the field

Mature Size

At maturity, the emerald green arborvitae may reach heights of 10 to 15 feet and spread 3 to 4 feet above the ground. To accommodate their final size, new shrubs need to be planted some distance away from each other and such structures as fences and walls. As they develop and grow, they will fill up the areas in which they have been planted quite beautifully. 

Where Do They Grow Best?

The emerald green arborvitae is a subspecies of the American arborvitae, a conifer that is indigenous to the northern regions of the United States and Canada. It is hardy up to USDA Zone 3, which allows it to grow in many of the United States’ more northern locations. It also grows well into Zone 8 and occasionally even into Zone 9.

Arborvitae need a soil that is neutral to slightly alkaline in pH, is rich in moisture, and drains well. Because the roots of these shrubs do not appreciate wet soil, it is important to add a thick layer of compost or mulch over the root zone each year in order to maintain an adequate level of soil moisture.

top view of an american arborvitae plant

How Much Sun Do They Need?

It is best to grow the ‘smaragd’ variety in either full sun or moderate shade. In general, it needs a minimum of 6 hours of sunshine each day; however, an excess of direct sunlight may put stress on the plant and cause the leaves to burn. On the other hand, they should not be planted in areas of complete shade since this may significantly decrease the density of the plant’s leaves.

Tips to Optimize Growth Speed

When designing a garden from scratch, it’s usually a good idea to have select plants that mature quickly. When it comes to ‘smaragd,’ which likes to take its time, there are a few things you can do to promote faster growth.

Have a look at these helpful hints:

1. Plant Appropriately

To reduce the amount of stress that is placed on trees and shrubs during the planting process, it is ideal to do it while they are not actively developing. This often occurs in the latter part of winter or the first few weeks of spring, depending on the severity of winter and how quickly the soil can be worked.

2. Water Appropriately

Newly planted trees need an average of 20 to 30 gallons of water each week, which is equivalent to between 1 and 2 inches of rain. After the first or second growing season, the root system will have been sufficiently established for you to gradually reduce the amount of water you provide.

emerald green arborvitae thuja occidentalis plant

3. Space the Plants Correctly

To get both shade and shelter, emerald green arborvitae are often planted as hedges. That means the shrubs are often planted too closely together, which can stunt their growth.

When you first plant the shrubs, leave a space of at least 4 feet between them. This will allow the plant to expand into the space.

4. Winter Care

If you live in an area that receives snow during the winter season, you need to make sure that your arborvitae are well prepared to weather the cold season. Arborvitae are tough and resilient, but you still need to remove the snow and ice that accumulates around the trees’ trunk and on its limbs. Leaving it on the shrub will harm the tree, limit its development, and cause disease.

Covering your arborvitae with a mesh prevents the snow from accumulating by forcing it to glide off the mesh. This makes it easier for you to provide the proper care even during snowy conditions.

Alaine Connolly
Alaine has been working way too hard in horticulture since 1992, beautifying golf courses, resorts, and hotels. She is a part time landscape designer who works full time caring for a 28,000 square foot public garden. At home, she maintains her own 400 square feet plot. Alaine lives in northern Illinois - zone 5b.
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