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Drought, Mulch and Adventitious Roots
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<Chris reid>
posted
Hi,
Question on how to respond to adventitious roots from overmulching. I have a customer (I am landscaper, not arborist) with too-deeply planted trees and shrubs. Read an interesting article by Sharon Douglas at UCONN about how even minor planting errors combined with drought can result in stress/disease. There were infestations and disease in many of these relatively new trees/shrubs (about 2 years in ground). Some are planted okay but have maybe 6 inches of bark mulch on them -- I tried to pull some of it back, but found some roots going through and stopped, without knowing how to decide whether to pull back mulch and if so, at what time of year. Should the adventitious roots get clipped and let the plant figure out what to do about it? How many adventitious roots constitute "a lot"? Species in question are rhodos and a norway spruce. Thanks -- I asked three arborists and nobody really was confident they knew what to do. Can I do something in steps, such as gradually reduce the mulch and aerate/improve drainage to try to create conditions under which regular roots would be stimulated to grow? I am happy to have an arborist do all this, I just want to make sure that however we proceed, we are proceeding with good information/a careful plan (either to do something or do nothing). Thanks. Chris Reid
 
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<Scott>
posted
Reply to post by Chris Reid, on February 19, 2003 at 23:59:16:

Sharon Douglas is actually at the CT Ag Exp Station in New Haven, not UCONN. Call her there, she's very helpful.

In general the biggest issue is near the trunk. You don't want trunk tissue burried. Get the mulch off the trunks and I'd say clip any adv. roots developing in that area.

I'd also guess the Rhodos are going to be less sensitive to the outer areas than the spruce. I think the thing you want to know is if the roots have grown outward from the original root balls (if the Rhodos actually had real soil balls). If the roots are spreading outward then clipping adv roots above the original balls (what 2-2.5'?) probably won't be a problem. If not, the plants my be relying on those new adv roots and it might be better to go slowly. In any case encourage root growth outward by proper irrigation if needed (last Summer was very dry, this Winter we have lots of soil moisture going into Spring) and soil amendment if needed.
 
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<Chris reid>
posted
Reply to post by Scott, on February 19, 2003 at 23:59:16:

Sorry, you are right and I stand corrected, Sharon Douglas is at the experimental station and that is separate from UCONN. I did discuss this matter with her on the phone, and she was clear that the problems could occur, and what the correct planting would look like, but I did not leave the conversation clear about how and when to remediate.

Thanks for explaining what the critical areas of concern are.

I see I did not completely ask my questions, in that most of the trees (which include 3 bradford pear, 2 prunus with red leaves, 1 cornus, 1 large caliper prunus with green leaves, 4 white pines and a Crimson King norway maple) are planted too deep in compacted, hard, soil that I think I would call subsoil -- don't know if this is technically accurate but in any case, I would want to see it more porous and with more organic matter. I did excavate around the trunks to expose the flares. Are there any other considerations in this soil situation with these trees, or should I continue as described for the mulch? Thanks.
 
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<Guy>
posted
Reply to post by Chris Reid, on February 20, 2003 at 05:41:37:

If you excavated to the flares then apparently you cut all the adventitious roots. If they were small that's fine, and I agree w Scott about encouraging lateral root growth as #1.

If they're in hard clay the aeration may be more essential than irrigation, since too much water will drown rhodos etc. I use a miner's pick to break up the area outside the soilball to help drainage and encourage outward root growth. The holes get packed with compost and soil conditioner and nutrients based on a test.

It's a common problem down here with our clay soins and underinformed (some w BS in Hort) installers.
 
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<Chris reid>
posted
Reply to post by Guy, on February 20, 2003 at 16:37:34:

The soil where the trees were too deeply planted was dry and hard. Technically we don't have clay here, I am told, but the soil was very hard to moisten and soften -- not a lot of air spaces and water just wouldn't sink in. Digging was pretty difficult. Kind of like carving with a soup spoon. In this dry hard soil, there were some very occasional roots coarser than fibrous which I did see and I didn't cut them -- worked around them and left them under a 2-3 inch coarse pine bark mulch I laid down (probably a meaningless effort in terms of the roots' viability, in retrospect), but to be honest, I didn't see a whole lot of roots in this compacted soil near the trunk. I think whatever tried to form there got fried. I will look to see whether there is root activity moving out to the sides, or whether these trees -- which received little supplemental water during much of the drought and superficial watering along with the lawn for the other part of it -- even have been putting out much growth at all.

Thanks, Scott and Guy, for taking the time to respond and provide perspective and advice.
 
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<James Causton>
posted
Reply to post by Scott, on February 19, 2003 at 23:59:16:

This happens to be a very timely and interesting discussion for me personally. I just, yesterday. inspected a client's site where 80+ trees of 2-3 inch caliper had been buried beneath 12+ inches of mulch. The inspection revealed massive amounts of adventitious root growth, leaving me wondering whether the adventitious roots are actually "feeding" the trees. On trees this small and this young, removing all the adventitious roots could be fatal. It could also be that, a younger plant will "adapt" to this environment. The plants are showing signs of stress, they are not putting on terminal growth and they are also showing weakness in structural root function. I am not sure that that data, or information, exists which quantifies the role that adventitious roots can, or do, exists. I would imagine that Jim Clarke and Nelda Matheny might have some serious input into the discussion.
I am inclined to recommend removal of all 80+ trees on the site and replant in an appropriate manner,

James.
 
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<Guy>
posted
Reply to post by James Causton, on February 20, 2003 at 05:41:37:

James,
New roots of the trunk do indeed work for the tree; that's why they grow. I looked at a bunch of buried willow oaks and riverbirches last year and recommended stimulating lateral roots on the oaks after exposing the flare. IME recommending replacement is seldom carried out so what's the point?
The riverbirches however had such vigorous adventitious roots that I couldn't
see cutting them and just left them to replace the buried original roots.

If you want data go to any floodplain and dig up trees that have been silted over and grew roots at a new level. It's been happening for millennia and some sp. are obviously able to handle it IF they survive the transition period.

For the oaks on that job I recommended the owner give the oaks 2 yrs to adapt and reinspect. If they aren't growing then it's replacement time.

Bottom line: if the new roots aren't thick cut em, if they are then you gotta think first. Many times replanting is called for and copies of the ISA's New Tree Planting brochure provided to the landscapers so they might do it right the second time.
 
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<Chris reid>
posted
Reply to post by Scott, on February 19, 2003 at 23:59:16:

As Scott suggested, I re-contacted Sharon Douglas, and thought others would benefit from her reply. Here ya go:

Hello Chris-

Good questions!! Problems with overmulching are becoming more and more frequent with the increased popularity of mulches in the landscape. Many people think more is better.... And, you're correct in your observation about the lack of information on how to correct problems with overmulching- it is really more of a "judgment call" than an exact science. Unfortunately, many plant care professionals are doing exactly what you're doing- cleaning up the messes made by others.

Since most root growth occurs in the spring and fall (associated with cooler temps, adequate moisture), I suggest that you start pulling the excessive mulch away from the bermed beds as soon as you can work the beds this spring. Rhododendrons are notorious for readily rooting into mulch although many other shrub and tree species can root into mulch as well. Oftentimes this is due to problems with the overall health of the rest of the root system- has it been suffocated by the thick mulch? is most of the root system dead? Death from overmulching is a slow process- the plants show poor vigor and generally decline; often with off-colored leaves or needles. As you'd imagine, they are also more susceptible to insects and diseases.

Assuming that the root systems of the ornamentals in your client's bermed beds are still healthy, you'll have to go on good faith that those roots can support the plants after they lose the superficial roots in the mulch and that they have the capacity to regenerate new feeder roots at an appropriate position in the berm. In a study with overmulched boxwoods that were just beginning to show symptoms of decline, removal of the excessive mulch (and associated roots) resulted in complete recovery of the plants within two years.

I have an article from American Nurseryman (April 1, 2001) that discusses overmulching and suggests a few ways of rectifying the situation. It is not in electronic form so if you're interested in a copy, please send your complete mailing address and I'll send you a copy via conventional mail.

I hope you find my comments helpful. Please don't hesitate to give me a call if you want to discuss some of these issues in greater detail.

Sincerely,
Sharon


Sharon M. Douglas
Plant Pathologist
Department of Plant Pathology & Ecology
The Connecticut Agricultural Experiment Station
123 Huntington Street, P. O. Box 1106
New Haven, CT 06504-1106
 
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