Backfill....

[logantree]

Greetings,

I've got a customer with a large oak tree in their backyard. I've attached the photos so you can see what I'm concerned about. I think the concrete was put there about 20 years ago, and I'm pretty sure they backfilled about 5-6 years ago. I've requested they find out for sure about the times. What should be done about this?

Thanks in advance.

 

[BC WetCoast]

In my opinion, any impact the concrete patio has had on the tree root mass has been overcome by the tree, so this is now a non-issue.

Same for the backfilling, although I'm having a difficult time figuring out what was backfilled and how much. My suggestion would be to lower the backfill that is against the trunk back to the trunk collar as best as possible, but don't remove the backfill in the rooting zone as it will probably be filled with fibrous roots.

Just from the picture, the canopy looks lush and healthy.

Get rid of that ivy.

 

[ATH]

I'd absolutely agree that the damage done by the concrete has either been overcome or such damage is beyond overcoming.

HOWEVER, the backfill damage may just be starting to show up. How deep is the fill? I see a LOT of trees with 12"+ of fill in new subdivisions that don't show the damage from for a few years. Often it is not obvious enough for the homeowner to call until the tree is half dead 10 years after the backfill was put in place (when the house was built). I'd also disagree about not correcting it. We see very good results if caught early enough. Is air excavation an option (AirKnife or Air Spade)? If so, this is a great way to remove the fill/restore original rooting area for the tree.

Even if complete re-grading is not an option, decompacting the added soil and introducing more pore space can really help aleviate some of the problems. Remember roots need oxygen. If air excavation is not available to you, consider at least vertical mulching with a small auger (or 2" auger bit on drill) and filling those holes with a good mix (compost & diatomacious earth or perlite).

 

[pdqdl]

Is the customer willing to spend money correcting the problem? If they don't want to spend the money, then all tree health considerations are pointless. Wait for it to either die or perhaps do just fine.

The grade looks like it would be possible to excavate around the tree, build a small, semi-circular retaining wall on the upslope side, and allow the tree to send roots up for air wherever it could. The terrace would be built so that the soil drained downhill away from the tree at it's original grade, yet still supporting the concrete on the uphill side.

Since it looks healthy otherwise, I suspect the tree has managed the soil compaction & deep root cover adequately. Trunk decay from being buried too deep is a different issue. Fix that, and the tree should be good for many years to come.

 

[S Mc]

I'm trying to figure out how the patio concrete can be 20 years old and yet the backfill was only put in 5 to 6 years ago. What was holding the concrete in place prior to the backfill?

It will be interesting what your client says on the time table. Also ask them exactly what the terrain was like prior to the backfill.

The crown does look pretty healthy, but there have been documented cases where oaks have been backfilled, developed an adventitious root system which kept the tree appearing healthy and then failed 30 years after the initial assault.

So I would definitely try to get as much history as you can.

You also have to be concerned about any impact you create that will affect neighboring properties (I'm looking at the fence, is this the property line?), the sloped hillside, and what your regrading or restoring of the natural grade will do to the concrete pad, etc.

There are hostas around the base of the tree. How damp is this area being kept? Very few trees like to stay damp at the root collar, combined with the backfill, this could be creating addition problems.

Sylvia

 

[logantree]

I'm trying to figure out how the patio concrete can be 20 years old and yet the backfill was only put in 5 to 6 years ago. What was holding the concrete in place prior to the backfill?

The backfill is 15 years old. The house was built 20 years ago, and then backfilled 5 years later. The land just sloped off right beyond the concrete. They backfilled to make a yard.

There are hostas around the base of the tree. How damp is this area being kept? Very few trees like to stay damp at the root collar, combined with the backfill, this could be creating addition problems.

I'd say it gets a good bit of water from the drive. It does drop off right behind that fence though. The fence is the line, but it's all woods beyond it.

I'm not sure how much they are willing to spend on the tree. I know they don't want to lose it, but I'm not sure they're interested in spending a lot on it...You know how it goes.

The tree does have a few very large dead limbs in it. You can also see a spot about 25 feet up where it looks like the tree twisted at some point, and has sealed off.

It's weighted and leaning towards the house, which is the reason I expressed concern with the backfill and possible root damage. I think they are very interested in finding out how great a threat the tree poses.

Thanks again.

 

[S Mc]

This is a tough one, because I sure don't see a lot of room for working the roots. They brought in backfill to create a yard, and it would take excavating most of that to see what has gone on.

A plus, if you will, is the sloped land that is, hopefully, at original grade. This would be allowing aeration and moisture to the roots to which they were accustomed. The undisturbed area also appears to be on the off side away from the house, which presumably would have more holding power, anchoring the tree from falling into the house. (Barring erosion on the hillside exposing those crutial roots.)

With the limits posed by workable area, and client's desire, I would at the very least recommend removing deadwood and perhaps lightening the heavier limbs growing towards the house, if acceptable reduction cuts can be made.

Sylvia

 

[pdqdl]

Piece-o-cake.

quote a nice profitable figure to excavate the stem down to the roots and build a little retaining wall about 1 foot away. Be sure to include plans to build the wall on the fence side so that critters are excluded and water can run out.

Then give them a comparison quote for removal, with the advice that someday it will become necessary, but probably not right now. Remind them that trees can blow over at any time, even without any detectable problems.

Offer no guarantees about the health of the tree, and just suggest that excavating the trunk will probably prolong it's life.

I would guess that is about $200 worth of digging and rock stacking, exclusive of material expense. Depending, of course, on how fancy you get with the wall.

 

[logantree]

I'm not exactly sure what you mean by building a wall...So I need to remove the dirt so the root flare is visible, and then build the wall about a foot from the root flare? What exactly is the point of the wall? (As you can tell this is a learning experience for me, so please forgive the ignorance.)

I did think that a root feeding like was mentioned would be a good idea.

Thanks

 

[S Mc]

ATH mentioned above that he has found remediation to be beneficial if performed soon enough. The initial negative impact to this tree happened 20 years ago with the construction of the house and patio. Further changes made 5 years later with the backfill.

The backfill is not the only contributing factor here.

Some oaks have a "good" tolerance for construction damage and fill (Matheny and Clark, 1998), depending on species and site characteristics.

As the issue with this tree is the negative impact to it's root system, and the subsequent loss of aeration. So I don't see the benefit of deep-root fertilization here. The tree does not appear to be lacking in nutrients.

Sylvia

 

[pdqdl]

What I am suggesting is to dig the earth away from the trunk, excavating down to the root flare, where it should be.

Build a small retaining wall on the uphill side of the tree trunk, so that the grade does not wash out and re-cover the tree or erode the pavement nearby. Build it about a foot away from the trunk, so that there is room for additional growth.

This doesn't look like a big project that would take a decent landscraper only a couple of hours to do the whole job. A tree man that gets blisters when he walks past a shovel might be a different situation. Bid it according to your skills, or maybe find a landscaper that works with wallstone on a regular basis.

I consider that it is too late to do too much for a root zone buried for 20 years.