Thuja occidentalis-the species-is among our very longest-lived species. Cliff dwellers on the Niagara escarpment are estimated to be thousands of years old. Even "run-of-the-mill plants growing in the Wisconsin woods can easily last centuries, if allowed to. The lifespans of the various cultivars should also be of extended length. 30 or 40 years is just getting started.

specimens of the Thuja occidentalis 'species' live for centuries ... all Thuja
occidentalis 'cultivars'

==>>> i dont know if we can make the leap from species to cultivars .... i will have to ponder this more .. and come back ...

cultivars other than green have less vigor ...

and then we would have to think about why certain plants are dwarf ... could they be virused ...

also ... we would have to think about age potential in their native perfect range.. and us planting them in landscapes far from native conditions ...

ken

"we would have to think about age potential in their native perfect
range.. and us planting them in landscapes far from native conditions
..."

This statement says a great deal :-) Trees under cultivation - grown in a garden - tend to live shorter lives than those growing in a natural setting undisturbed by us messing them about. It's a pretty broad generalization but when you consider all the factors in a garden setting than can affect the lifespan of a tree, it does make a fair bit of sense. Most landscapes or personal gardens in this country are only decades old to begin with (if that) rather than centuries, so unless you are looking at gardens/cemeteries/estates back east that have been around for more than 100 years, it's a bit difficult to judge exactly how long some of these trees will live. And if you consider that the vast majority of cultivated varieties have only been in existence or available for decades rather than centuries, it is again very difficult to predict exactly how long they may live.

Most of the trees that are considered "heritage" trees or are large, long-lived examples of their type are species rather than cultivars. We humans are rather new at this business of tree creation :-)

In addition to gal's excellent treatment here, I would only add, this is inherently a long-lived plant. Sure, mucking around developing these cultivars may have inadvertently taken out some characteristics that conferred health and longevity to the plant, but in most general terms, these are long-lived plants. You want a number stuck to that? I can't do that-far too much happenstance out in the landscape to make predictions of that sort. But it would be hard to imagine a scenario where the lifespan of any arb cultivar would be the limiting factor in any landscape composition.

The perhaps more relevant
question to average gardeners is when an old tree stops looking good. The whole
thing is perhaps a little like looking for a bride, can't be too young, can't
be too old.

I am currently
looking at the Thuja occidentalis
'Woodwardii' which for my particular use becomes good looking only at 3' x 3' or
larger but I can buy it only at 2' x 2' or smaller. So, I have to wait for a
couple of years for it to look good, and then ... for how long can I enjoy it
looking good? 30 years would be good, but I have had trees that became ugly
looking much sooner than that.

In other words, what is the useful life span of Thuja occidentalis cultivars?

I found this information on the web:

http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=c242

Noteworthy Characteristics

Thuja occidentalis, commonly known as American arborvitae, Eastern arborvitae, Eastern white cedar or Northern white cedar, is a dense, conical to narrow-pyramidal (sometimes maturing to broad-pyramidal), often single-trunked, evergreen tree that is native to eastern and central Canada south to northern Illinois, Ohio and New York with scattered populations further south in the Appalachians to North Carolina. ‘Woodwardii’ is a compact globular-spreading form that typically grows to 4-5’ tall with a spread to 8’ wide over the first 10 years. It may eventually mature to 8-10’ tall and to 15’ wide. Plants display attractive scale-like rich green foliage in flattened sprays. Seed cones, if present, are not particularly showy.'

Edit: You can sheer these from what I understand. Which would control the growth quite a bit, if done on a regular basis.

You missed the point of this thread. The point is longevity of the plant, either in absolute terms (from germination to death) or in relative terms (useful life span of the plant for a gardener).

Well, you did ask for thoughts. :) But read between the lines. If it's 60% of it's maximum height @ 10 years, then it probably is only a 30yr shrub. How it acts during that time would be dependent on zone climate, soil moisture and the kind of care and maintenance it gets. I've seen pretty nice specimens at 30 years, then to I've seen some pretty ratty looking ones at 15.

Either way, you're probably pretty close with your first estimations of it being a 20-30+- year shrub.

I suppose the lifespan of a lot of trees, cultivars included, depends on how much room they have to grow when planted in the garden. Most, sooner or later, outgrow their spot and are removed.

This^. 'Woodward' is going to get big. I used it as a never-to-be-sheared hedge in yard as a sweeping curve, on five-foot or 6-foot centers or something like that. It has developed perfectly, to where if the homeowners wish to see beyond their patio, they stand up. When seated, they are secluded by this row. But ultimately, the line is going to take up quite a bit of real estate. already is. Something like fifteen years in the ground, plants are now head-height and growing.

You overall question may have some academic interest, but for general purposes, it depends entirely on which cultivar, planted where, by whom, with whatever expectations they bring to the table. Too many moving parts. Species is inherently super-long-lived.

Old eastern arbs planted in cemeteries look ageless. Trimmed-off branches down low show exposed wood that is immensely weathered, but never rotting.

Wood is heavily imbued with resins. Fence posts, poles, decking, shingles.....the wood of this species was always favored for all weather-exposed uses.

Longevity from germination to death may be of academic interest, but useful life span for a gardener is of practical interest, it's useful to discuss the many factors that play a role.

Cemeteries have organic matter, no wonder old eastern arbs and other plants do well there :-)

I may be making a contribution to that organic matter some day.

Listings of record trees include examples of cultivars that go back a ways. For instance a Thuja plicata 'Zebrina' measured at Stourhead in England during 2006 is known to have been planted in 1906. This cultivar does vary from the type primarily in having banded foliage, otherwise it still forms a large, apparently structurally sound tree. Many other conifer cultivars may instead have markedly aberrant growth forms that make them prone to falling open (columnar) or overwhelmed by adjacent plantings (dwarf), killed by other adversities such as cold (fixed juvenile) or drought (miniature). And any grown in containers at any point in the production and sales sequence may be planted in their final positions with unresolved root deformities that result in eventual girdling or toppling - on the market here grafted conifers appear to be routinely presented with corkscrew, j-rooted or otherwise severely misshapen root-stocks being involved. Cultivated examples of wild species will of course also be subject to this latter occurrence - but the additional vigor these often have may perhaps tend to help them overcome it and remain standing much of the time. Redwoods for example seem to pretty much never go over, regardless.

What I have seen with T. occidentalis 'Woodwardii' specifically is that with age it tends to open up and separate into a low tree-like shape instead of remaining as a compact "globe". Perhaps this results in failures (splitting apart) in snowy areas or simply in a tendency for specimens having reached this condition (and size) being removed due to how they look (and how big they have become).

We used to have a couple here, planted as foundation shrubs and that is what happened to them - as they increased in size they leaned away from the house, overwhelmed their positions, started to become uneven in shape and were removed. Many people buying a plant like this will be looking for a small ball ("globe") and become disenchanted when they end up with something big and lumpy.