Thuja occidentalis 'Nigra' / black arborvitae

Thuja occidentalis 'Nigra' is a compact, conical selection of eastern arborvitae with exceptionally dark-green foliage that retains good green color in the winter in cold climates. After 10 years of growth, a mature specimen will measure 6 feet (2 m) tall and 3 feet (1 m) wide, an annual growth rate of 6 to 8 inches (15 - 20 cm).

This is an rather old cultivar in the nursery trade that unfortunately is of unknown origin. It is thought to have originated in the USA in the 1930s. L. H. Bailey formally described it in his 1933 book, Cultivated Conifers in North America.

An attractive grouping of Thuja occidentalis 'Nigra' in an arboretum setting.
Photo by Jesse Saylor
Thuja occidentalis 'Nigra' — a closeup of foliage detail.
Photo by James H. Schutte


Carolyn Wenstrup

We planted a Thuja 'Nigra' (arborvitae) in the spring. Now that it is fall it has a lot of brown ... is that normal?

David Olszyk

Hi Carolyn, it's perfectly normal for this species to shed up to 25% of its internal foliage every fall. In your case, it was almost certainly amplified by the fact that you planted in spring (that's a really bad time to be planting trees in most parts of the country).


Is this article describing a miniature Black cedar (Thuja Nigra)?. Other sites list it's height of up to 20 feet when here it states to only grow up to 6feet.

David Olszyk

absolutely not, Hector! ... it's describing an intermediate-growing arborvitae (not cedar) that has the cultivar name 'Nigra' because of its exceptionally dark foliage, particularly in winter.

As for the growth metrics: 6 feet in 10 years / 20 feet in 25 to 30 years is correct and extremely accurate. Miniature implies a foot or less of growth in 10 years.


I have planted around 100 of these on my property last fall. Growth and colour seem to be on track, but I was wondering if any fertilization would be recommended before winter hits (hardiness 6a-6b)? I have read bone meal can be useful, but other sites state that no fertilizer is required.

Any advice is super appreciated!

David Olszyk

Isaac, NEVER apply fertilizer to the landscape unless a soil test reveals that you're deficient in something. Applying bone meal to the soil surface doesn't do anything, but it's handy for establishing bulbs when planting in the fall.

Millie Rogers

Really enjoy reading all the questions and answers. Thank you for that.
We just planted an eight foot black cedar in our back yard for privacy. We live in Oakville a very urban area. Our soil here is clay. The people who planted it for us told us to keep it well watered. Can you give me a little more information on the watering i.e how much and how often?
Thank you.

David Olszyk

Hello Millie ... since there's an Oakville in every state, it's going to be a little harder to answer your question. The general answer is that you'll need to keep a close eye on irrigation for the first five years. In order to determine whether it needs a drink, thrust a finger into to the soil up to the second knuckle. If it's dry, water it. If it's damp, check again in a few days.

Millie Rogers

Thank you David I really appreciate your response. I should have told you our location is in Oakville, which is in southern Ontario Canada.

David Olszyk

see? ... that's a huge difference. I assumed Oakville WA, or Oakville, CA ... in the case of Ontario, you should be good until spring. Make sure the soil is damp, then wait for everything to freeze. It would also be a good idea to mulch and wrap if that's your thing.

Ronald Schlak

And with a plant that size , Millie , a slow watering with a hose on a trickle will ensure water gets all the way down the root ball