Welcome aboard, Shastensis, and what a nice job you've done with these photos! Perhaps more surprising to me than the glaucous foliage of this species is the departure from the Thuja norm in it's bark.

What hardiness rating has been assigned to this species?

+oM

Although upright plants can be found on the market since 'Glauca Prostrata' or 'Prostrata' seen at outlets are liable to be cultivariants (rooted or grafted side-branches) these may produce leaders later.

It has been rated as "zone 5" but its hard to tell as its so rare and there is no widespread experience of it in that climate.

Several years ago I received a blue Thuja koraiensis form under the cultivar name 'Glauca' which shows the same colour as the one's at the pictures.
This blue colour is outstanding in combination with the silvery underside of the foliage.

I don't know if the blue one's will grow also in nature as a natural variety just in the way the Cedrus libani var. atlantica 'Glauca' was found.
The thing is that the Thuja koraiensis species does have a green foliage colour...

Thuja koraiensis at the Denver Botanic Gardens. Not sure whether this is a cultivar.

Nate, the one at your picture does also have a blueish colour.

Here's a pic taken at my Pinetum from both one's, the species and the 'Glauca'
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Hi. I bought a couple from Hulsdonk nursery in the Netherlands two years ago. The guy told me he had the greatest trouble selling these. One I planted in the garden and did well, until a couple of weeks ago when it suddenly shrivelled and died ; the other one is still in it's original container and is doing fine.
Is this plant fussy with regards to soil ph, or could it be the heat and drought? From what I read in the original poster's message, this wouldn't seem to be the case ? T.

The only source I've been able to find on the internet for the straight species tree, not the "prostrata" cultivar is here:

http://www.lazyssfarm.com/Plants/Shrubs/S-Z%20Shrubs/S-Z%20Images/thuja_koraiensis.htm

The specimens in Sonoma County were irrigated their first few years in the ground, though I do not believe that they are irrigated anymore. Not sure what could have killed your plant.

I am having trouble recognizing why this plant is so hard to come by. It such a beautiful tree and seems very desirable, almost more so than green giant or any of the T. occidentalis cultivars. It is nearly impossible to find seed-grown trees of this, even in most botanic gardens. How rare is the tree? There is also little information on it on the gymnosperm database or on the internet in general. Perhaps Resin could pitch in here and add something?

From Farjon's Cupressaceae monograph:
Conservation: This species is apparently rare and occurs in isolated populations, one in China and the others in North and South Korea. The population in China is in the Changbai Shan Nature Reserve but the Korean populations are mostly outside protected areas. Most of the known collections have been made many years ago and it is presently unknown in how many localities it (still) occurs and what its status is. IUCN: DD [Data Deficient]

Resin

Thanks guys. Interesting species.

So Coniferjoy, are you saying that the 'normal' species would have green foliage, with just the cultivar 'glauca' being the, well.......glaucous one?

+oM

I would assume that the species itself is pretty glaucous to begin with, a few individuals being more glaucous than the rest. The white stomatal lines can appear on both sides of the foliage, too, not just the undersides. I observed this on the quarryhill specimens. I was told who collected this clone, but I forget. I do not believe that it was a cultivar, but rather the straight species. Perhaps it is more glaucous in the hot, dry Sonoma County climate.

One thing that sure amazed me was how coarse and rough the foliage was compared to other species of Thuja. I was not expecting that.

I was also shown a cutting that is reported to be Thuja sutchuenensis but is more likely T. standishii. It was found at a garden in New York State by Silba and given to QBG.

14048 1 gal pot Thuja koraiensis / KOREAN ARBORVITAE
$16.00

Here is a link that might be useful: Spring Price List - 2010

Hi Tom,
I received the green one from which I always thought that it was the species about 15 years ago.
In 2004 I received the blue one which was labeled as 'Glauca'.
So for 9 years I was only familiar with the green one...

Quick thinking after I red Pineresin's comment:
The species from China or from Korea could be differend in colour, one is green and the other is blue which could be a natural variety...

Amount of bluishness could vary in wild stands, as it does with various other conifers. Here there are occasional glaucous Thuja plicata seen. A funny thing is that a green one near me turned glaucous one year, several years ago and has stayed that way. It is maybe 50' tall.

Maybe the 'Glauca' Korean arborvitae is a type that pops up in nursery seed beds, as does the 'Glauca' Nootka cypress.

Bboy,
as far as I know, seed of Thuja koraiensis is virtually unobtainable. I am curious how many separate individuals represent all the clones in this country and when they were introduced and by whom. It would be nice to eventually procure seed of this, though I have no idea how it would be possible and there seems to be little drive to do this. It is unknown, after all, how threatened or rare the species is in it's habitat.