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Arborvitae drought tolerance

Posted by spruceman Z6 VA (My Page) on
Fri, Sep 25, 09 at 16:18

During my visit to the Va Arboretum yesterday I saw two young Thuja plicata "atrovirens" growing on a dry south facing slope where other trees struggle. These were as lush and green as could be. And this summer--since very early August, at least, has been unusually dry. All the grass around here is mostly brown now.

So, is Thuja plicata especially drought tolerant? Thuja plicata in its native range usually grow on sites that are not drought prone, if not generally rather moist. Could we have a case a little like the bald cypress, that usually grow in swamps, but does well on dry sites?

I have two T. plicatas growing on my yard near Winchester, VA., and they are showing no stress at all either.

And finally, I have Green Giants that are doing well also. They did stop growing early this year, but they look fine.

And what about T. occidentalis, the so-called northern whitecedar. It seems these may be drought tolerant as well.

So, what have you folks observed? Thoughts? It has been so dry recently I have had to water a lot of stuff. A lot of my trees, even thouse that I planted 5 years ago or more, are showing stress. But it is difficult to water everything. I have not watered any of my Thujas. Should I when we have a severe drought? Or can I leave them be, as I do my Norway spruce and the more established oaks, etc.?

--Spruce


Follow-Up Postings:

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RE: Arborvitae drought tolerance

Spruce

I'm often surprised at the apparent drought tolerance of this seemingly moisture-loving genus. Native Thuja o's up here seem to shrug off a dry summer like we've had. Some near roads and such do seem a little weaker but even those mostly come through ok. One thing that does get them though is to go into winter too dry, and then, to have lots of super-cold, dry winds during the winter. You can lose a few that way, esp. in exposed sites.

I have a grand total of three GG's up at my land. They're coming along just fine with basically no help from me. One of these, bigger than the other two and planted late last summer, did look pretty well burned up through the first half of this summer but is now, somewhat inexplicably, doing fine. I think they're hard to kill!

Thujas are to me the quintessential plant that just bides its time, waiting for better days.

I'm happy to say there is some rain moving through these parts tonight. Nothing real impressive, but enough to help.

+oM


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RE: Arborvitae drought tolerance

"Thujas are to me the quintessential plant that just bides its time, waiting for better days."

Tom, what a great line. I love that!

I'm in Wisconsin sand country and my T. o. laughs off any droughts thrown at it, which seem to come with all too much frequency lately. Once established, they remind me a bit of Swamp White Oak. They may prefer moist conditions, but perfectly capable of withstanding drier conditions.


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RE: Arborvitae drought tolerance

I can tell you as a nurseryman that Thuja plicata and specialy the cultivar 'Atrovirens' are very dry tolerance.
This is because the roots of this cultivar are growing very deep straight into to ground to find the water it will need.
This cultivar is the most difficult to make it a good ball rooted.
Every year around this time it's time to plough with a big U-forming knive under these roots to cut off the mean roots and will start to make a compact rooted system.

Thuja occidentalis and it's cultivars do have differend rooting system, they will grow not as deep as Thuja plicata and it's cultivars will do.
In very dry years they have it more difficult and will start to make seed cones and will stop growing much soner then Thuja plicata's will do.


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RE: Arborvitae drought tolerance

Much of the coastal PNW where Thuja plicata is native is quite dry in summer. Excluding the Olympic rainforest area, much of the PNW receives far less annual rainfall than most areas of the east coast and sections of the midwest and virtually none of it during the summer months - it shouldn't come as too much of a surprise that these trees can be quite drought tolerant. And I'd question the notion of these trees being particularly deep rooted. This is a response entirely based on ability to access soil moisture. Here, these trees have a reputation for being extremely shallow rooted, with native forest specimens often growing in forest duff rather than the underlying soil layer. Given their potential for enormous top growth and lack of root stability, they are often prone to blow-overs, especially during wet, windy winters. You will frequently see upended rootballs 12-15' across but only 12-24" deep.


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RE: Arborvitae drought tolerance

From observations at Killeen, Tx of about. 100 tall mature Arborvita (either eastern or oriental), most of them survived the droughts of the last 2 summers (21" rainfall last year), but about 1 in 20 trees died. Smaller uncared for trees/bushes died at maybe 1 in 10 rate. This is a bit surprising for a tree from wetter and cooler climes.

In regard to Spruce's question about watering established trees, in severe droughts/heat spells (continuous days of 100 F + weather for us), I try to provide watering every 2 weeks to 30 days IF possible. Prioritize nut trees and trees in immediate yard.


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RE: Arborvitae drought tolerance

  • Posted by bboy USDA 8 Sunset 5 WA (My Page) on
    Sun, Sep 27, 09 at 12:33

>Given their potential for enormous top growth and lack of root stability, they are often prone to blow-overs, especially during wet, windy winters<

As far as it goes, this swarthy tree does not blow over - it is the redwood analog of our region, forming massive, firmly anchored trunks that survive thousands of years of gales that on wet, windy outer coastal sites may blow down entire stands of other species of trees around them.

For every one of these that I have seen get undermined by water and topple in high winds, I must have seen dozens if not hundreds of other examples of Douglas-firs, hemlocks etc.

Like other native conifers this one occurs on a broad range of sites including ones that are not completely suitable. "Flagging" (reddening and dropping of older foliage sprays in response to drought) is common and has been asked about on the internet multiple times that I know of. This record-breaking year even the sheltered grove of fairly old cedars (including a few old growth specimens) growing in a cold air- and water drainage on my friend's Island County property is showing obvious distress, with much flagging and perhaps a somewhat lackluster appearance to the remaining live foliage.

often forms pure stands on floodplains and wetland sites. As does yellow-cedar, western redcedar tolerates a nearly complete edaphic range, and develops a very dense root system; the latter feature may explain is abundance on very steep, seepage-affected, and often unstable colluvial soils*. Most productive on submontane, fresh to moist, nutrient-rich soils within cool mesothermal climates

--Klinka/Krajina/Ceska/Scagel, Indicator Plants of Coastal British Columbia (1989, UBC Press, Vancouver)

*Emphasis mine


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RE: Arborvitae drought tolerance

As far as it goes, this swarthy tree does not blow over - it is the redwood analog of our region, forming massive, firmly anchored trunks that survive thousands of years of gales that on wet, windy outer coastal sites may blow down entire stands of other species of trees around them.

There's more than a few sources that do not agree:
"Although they are as windfirm as Douglas-fir on dry sites, redcedars, are often windthrown in wet environments and are not resistant to windthrow on the moist sites where growth and yield are highest." (US Forest Service Publication)

"Because of its high susceptibility to windthrow in wet environments and in the moist sites where growth and yield are highest, western red cedars should not be left as scattered seed trees. Even those along clearcut margins may be lost to wind throw or exposure." (USDA National Resources Conservation Service)

Maybe not quite so "firmly anchored" as some would have us believe:


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RE: Arborvitae drought tolerance

  • Posted by bboy USDA 8 Sunset 5 WA (My Page) on
    Tue, Sep 29, 09 at 13:25

Grows large in places where it is too wet for other native conifers to occur much at all. So, individuals and patches of this species undermined by water and knocked over are seen. You can find blown over giants in all stands where such large trees still exist, regardless of species. The floors of old growth forests in this region are often criss-crossed with old logs of various sizes. The water stored in them has been said to be an important contribution to the ecosystem being sustained through rainless summers.


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RE: Arborvitae drought tolerance

This description could apply to almost any of a number of "timber" trees, which when grown in the open are very windfast, but when grow in a heavy forest with plenty of moisture, are subject to wind-throw etc when the rest of the forest is cut-away and just the individual is left.


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