Need privacy under high-skirted cedars

beckyhowie(7b)October 13, 2012

We have a dozen huge (30-50 ft tall) cedars along the south border of our back yard. The branches were growing way out into the yard making it look dark and claustrophobic, so I high-skirted the trees to about 10 feet. It looks much neater, but now we have lost some privacy. We can see right between the trunks (which range from 5-10 feet apart) into the neighbor's yard. What can I plant between the cedars to fill in the gaps that won't grow way out into our yard?

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bboy(USDA 8 Sunset 5 WA)

Too bad you can't reattach the branches. Now you will have to try and establish some tough evergreen shrubs in the dry and probably very rooty ground around them. And wait years for them to reach any size. If you put down bark mulch and water it during the summer birds may bring cotoneasters, hollies, Oregon grapes, common hawthorn, Photinia davidiana, English and Portugal laurels...fostering this process may work better than trying to dig planting holes and establish nursery-grown stock beneath the conifers. Trying to install specimens of much size, as you might try to do to get screening quicker could prove to be quite arduous.

    Bookmark   October 13, 2012 at 1:08PM
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PRO
George Three LLC

a fence?

    Bookmark   October 13, 2012 at 10:19PM
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larry_gene

You need to have Christo come in and drape sheets between the trees.

    Bookmark   October 13, 2012 at 11:26PM
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botann(z8 SEof Seattle)

Aucuba would be a good choice. It likes dry shade and can handle root competition better than most shrubs.
Mike

    Bookmark   October 14, 2012 at 12:11AM
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bejoy2(8)

What kind of cedars - Thuja plicata (western red-cedar) or one of the true cedars (Cedrus species)? It matters, because western red-cedar is allelopathic, and suppresses other plants growing within its root zone (I'm not aware that true cedars are allelopathic). But learning from nature, there are a few plants that do grow under western red-cedars. Mohonia nervosa (low Oregon grape), Polystichum munitum (western sword fern) and Gaultheria shallon (salal) are 3 very reliable native plants. If you'd like to look for a list of other suitable plants online, put the term 'plants for dry shade' in your search engine. Because, even though red-cedars love moisture, they mostly get it with their feeder roots, which extend beyond the dripline of the tree canopy. The tree's branches and foliage prevent rain from falling on the ground directly beneath the tree.

Whatever you decide to plant under your cedar, don't over-water them, because T. plicata is shallow-rooted, and if you modify the zone under the canopy, either by installing a raised bed, back-filling or excavating, you can damage the roots. Also, once you put your new plants under the tree, be careful not to water too much, since supplemental watering can encourage the tree to grow more shallow roots, as well as loosen the soil - both of which can cause the tree to topple in a windstorm or heavy rains (this is good advice for planting under almost every tree I can think of).

    Bookmark   October 14, 2012 at 11:03PM
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botann(z8 SEof Seattle)

You can add quite a bit of soil under a Thuja plicata, Western Red Cedar, without doing damage. They naturally grow on river floodplains and have adventitious rooting, even from the trunk.
Becky, the Cedar branches growing out of the trunk at ten feet and above, will eventually hang down and out, giving you back some privacy....and that claustrophobic feeling.
Bejoy, I didn't know that Western Red Cedars are allelopathic. It may be a common misconception. Red Cedar woodchips don't seem to have any adverse affect on plants when used as a mulch, or even tilled in the soil.

Mike

    Bookmark   October 15, 2012 at 3:39AM
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beckyhowie(7b)

Thank you, everyone, for some great info and ideas. I will talk to my husband and my neighbor to see what we all agree on. We probably won't do much now until spring, so we will have the next 6 months to get used to the new look. In spite of the loss of privacy, I'm still glad I did it. It does look so much more tidy. And eventually we will decide on just the right thing to fill in the gaps. Thanks again!

    Bookmark   October 16, 2012 at 2:36AM
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plantknitter(8)

understand your need to think about it, but fall is really the best time to plant.........

    Bookmark   October 16, 2012 at 11:25AM
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bboy(USDA 8 Sunset 5 WA)

If you water under arborvitaes on soils that dry out in summer they are likely to like it, produce more lush tops, thereby look better. Falling over because you watered? Naw. Western redcedar is the climax dominant in local wetlands, old stands in suitable situations will typically consist of associations like cedar, devi's club, lady fern etc.

All non-desert trees produce mats of shallow feeder roots just below the surface, whether there is watering or not. Not watering during a dry period merely results in, if anything some of these roots drying out and dying.

    Bookmark   October 16, 2012 at 1:14PM
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gardengal48

Mike, you are correct - that is a common misconception :-) Western red cedars (Thuja plicata) are not considered significantly allelopathic. They can, however, produce a lot of litter (needle drop) and that combined with a dense, mat-like root system and the heavy shade they produce tend to discourage a lot of undergrowth. But when they are limbed up and adequate irrigation and establishment TLC is provided, a good number of plants grow very happily in their presence. I've planted and grown a pretty wide variety of plants under the canopy of our native cedars.

    Bookmark   October 16, 2012 at 2:30PM
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bboy(USDA 8 Sunset 5 WA)

Like I said, all you have to do is mulch and water and carpets of spontaneous tree and shrub seedlings are liable to appear. So, yes, you can get such plants to grow beneath them.

Weevil prone kinds like salal and tall Oregon grape may be made into confetti by them, when located beneath evergreen trees.

    Bookmark   October 16, 2012 at 4:23PM
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bejoy2(8)

Western red-cedars are allelopathic. The kind of allelopathy that most of us are probably familiar with is the type exhibited by walnuts, and is a function of a biochemical produced in the roots (Juglans are also allelopathic in the leaves and wood). I'm not familiar with the specific mechanism for the delivery of the alleopathic components in Thuja plicata (the article says litter is the source, so it stands to reason that the more litter is present, the stronger the allelopathy will be). Unless it is a component of the bark or wood, I would not expect to find the effect in those components, so feel free to use cedar chips in your landscape. I've attached a link to a scholarly paper that plainly lists Thuja plicata as having alleopathic properties. If you remove the litter under the trees, you can probably grow a wide variety of plants just fine, since the allelopathic component seems to be the litter.

Roots grow on a cellular level, and it happens so quickly that if you were watching it under a microscope, you probably could not see it happen with the naked eye. So if you start watering a tree (any tree) shallowly under the canopy, those roots will grow faster than the roots that are deeper, or outside the drip line, which will slow down their growth - because roots grow toward water, and if there isn't water, they quit growing, or slow down their rate of growth significantly. It's basic plant biology! Accelerated growth of shallow roots under the canopy combined with slowed-down or halted growth of deeper, wider-ranging roots means that the tree can tip over if the soil becomes saturated, or in a heavy wind. It doesn't happen overnight, but it is inevitable, and the problem is that there are no symptoms or outward signs that a tree has shallow roots. The next time we have a windstorm, just go around and look at the roots of the trees that fell over. They are all shallow-rooted.

Botann, I saw your post on a thread on this same subject a few years ago, and I don't disagree that adding some soil under Thuja plicatas can be done without harm to the trees, because the roots that provide the water in a Thuja plicata with a full canopy is getting its water from beyond the drip line. As long as that continues unchanged, the soil under the tree is a non-issue. The problem happens when people put plants in that soil and begin to water them. The tree will send roots up into that soil, and if you don't continue to water the tree deeply or outside the drip line, it will eventually become shallow-rooted.

Plants are amazingly adaptable, and since they grow where there is periodic flooding and in fluctuating water tables, Thuja plicata must have devloped an adaptation to having soil washed away or heaped up around them and flood-and-drought cycles, especially if it happens on a regular basis. But sudden changes are more stressful to a tree than gradual changes, and if the change is too drastic or too sudden, the tree might not be able to recover. If a tree in a floodplain can't adapt and falls down, it isn't going to hit anyone's house. The Thujas we are discussing might be able to adapt just fine to any changes the original poster makes, but if it were me, I wouldn't bet my house on it.

Here is a link that might be useful: Allelopathy in Trees

    Bookmark   October 17, 2012 at 3:57PM
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gardengal48

Boy, talking about needing to press a point!! As previously stated, Thuja plicata are not significantly allelopathic. At best they are listed as "slightly" and that only the result of their litter (which can be considerable) but even that determination was made under laboratory conditions and is the subject of some debate. Testing has not determined any specific chemical contained/exuded by thujas that limits plant growth although there are quite a number that can limit insect and microbial activity. Many mistake the one for the other. And for the most part, any allelopathic characteristics a plant may possess are typically limited in application. Even juglone, possibly the most acutely allelopathic plant chemical we are aware of, has no affect on the majority of other plant species.

btw, most trees have shallow roots. The vast majority of all tree species have the bulk of their root system contained within the top 12-16" of the soil and with most feeder roots located just beneath the soil surface. Thujas are not different. I've yet to encounter a situation such as you predict after several decades of designing and gardening professionally. In most cases, the extra watering is only needed to get the new plantings established, which would hardly cause any well-established cedar (or any other tree) to topple over.

Here is a link that might be useful: the myth of thuja allelopathy

    Bookmark   October 17, 2012 at 7:07PM
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bejoy2(8)

gardengal48, I knew I could count on you to expand the conversation. Go ahead and quibble. 'Shallow' is a relative term. Besides the depth of the root zone, the distance to which it extends into the soil surrounding the tree also helps keep the tree from falling over, as I stated. Watering directly under the tree encourages both 'more shallow' rooting as well as discourages the roots from extending beyond the immediate area. And it isn't like this happens overnight. I'm not saying you are wrong, just that you are not 100% correct. There is a wide range of possibile outcomes, and you can't predict them any more than I can - unless you can see the future. But it seems to be very important to you that you are the penultimate expert, so I'm not arguing with you anymore. I encourage anyone who has questions on this subject to contact an actual ISA Certified Arborist. I know plenty of people who have worked in the landscape business for many years and don't know a Thuja from a Juniper. Just because you are a landscaper doesn't make you an expert. Having an education doesn't make you an authority. And being stubborn and opinionated doesn't make you right.

    Bookmark   October 18, 2012 at 2:02PM
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bboy(USDA 8 Sunset 5 WA)

More of same. If you don't want a debate, don't come on here and make debatable statements. It's that simple.

    Bookmark   October 18, 2012 at 10:48PM
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larry_gene

But in general, forums invite debates. Makes for good reading and is sometimes informative.

The above phrase "penultimate expert" is a curious twist for "ultimate expert", and for me has been the most intriguing part of this discussion!

    Bookmark   October 19, 2012 at 12:05AM
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botann(z8 SEof Seattle)

I have dug up a lot of stumps over the years with a bulldozer. Both on my varied ten acres and on the job. Thujas naturally grow in the wetter areas and have flat, shallow, root balls, especially shallow wet areas with hardpan close at hand. Planted Thujas are planted in all sorts of soils. When they are in light, gravelly soils, with hardpan a long way down, their rootball is a lot less flat and less likely to blow over. They are also a lot harder to dig up. You don't see those.
Dislodging preconceived ideas by the use of facts doesn't seem to be working. I will continue to use Thuja chips, including the 'litter' for mulch, and as a soil additive.
Mike

    Bookmark   October 19, 2012 at 9:07AM
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bboy(USDA 8 Sunset 5 WA)

The largest remaining cedars tend to have forking tops. I was told by a forest ecologist this is because these giant trees break off high up instead of blowing over during catastrophic winds, that may knock down almost the entire stand of hemlocks etc. around them.

    Bookmark   October 19, 2012 at 12:55PM
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gardengal48

LOL!! There is a great deal of difference in being "stubborn and opinionated" and having the education and professional training and experience to factually back up one's viewpoint. And I don't pretend to be the expert in anything, but as an instructor/educator and writer, I feel compelled to correct or modify misstatements and discourage the use of absolutes. I try never to state anything as fact that I am not prepared to support with an outside source.

Just ask bboy :-) He and I have clashed frequently enough over the years but - I would like to think - have finally come to respect each others' knowledge and experience. Which is considerable.

    Bookmark   October 19, 2012 at 4:43PM
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bboy(USDA 8 Sunset 5 WA)

Hey, well, thanks!

    Bookmark   October 19, 2012 at 8:24PM
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botann(z8 SEof Seattle)

That ended on a surprisingly happy note!
Mike

    Bookmark   November 1, 2012 at 2:04PM
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