Any Retaining Wall experts here?
 

I’m having an issue in a location where I want to plant a citrus tree. I’m about 2 feet away from a small retaining wall and I’m finding a shelf of concrete approximately 12 inches below ground. I assume that is part of the footing for the retaining wall, which is 4 feet high and holds back about 3’ of hillside.

I can easily smash the concrete with a sledgehammer, it only seems to be a couple of inches thick. There are reasons why I want to locate the tree in the spot because of aesthetics as well as spacing and sunlight. The tree is a dwarf lemon, fwiw, grows to about 8-10’ in good conditions.

My question is whether the concrete I’m hitting is essential for the integrity of the wall, I just don’t know much about retaining walls and how much footing they have around them.

I’m also dealing with hard clay 1’ down but that’s another subject. Here are some photos:
http://forums.pelicanparts.com/uploa...1532210159.jpg
http://forums.pelicanparts.com/uploa...1532210159.jpg
http://forums.pelicanparts.com/uploa...1532210159.jpg
http://forums.pelicanparts.com/uploa...1532210159.jpg

Thanks
In
Advance as always! :)

IMHO, you should be fine to bust out that concrete, Denis. 2' away is very far for any meaningful footer for a wall that short.

I bet the layer you hit isn't very thick....hopefully anyway.

Others can chime in but that's my take.

I would not do it.

Retaining walls are nothing to mess with.

The wall is actually an "L" in shape, you should not put a hole into the lower part of the "L".

The lower part of the "L" provides a coefficient of friction against the forces above that want to push/slide it across your lawn (lateral forces).

It needs to be able to resist lateral forces even when it rains and that clay soil swells and becomes as slippery as wet soap.

An "L" is an unnatural shape to build, as it wants to crack at the intersection, what holds this artificial creation of man against nature is steel in the form of reinforcement bars (rebar), and lots of them crossing and tied together in all sorts of tight patterns (a square grid typically).

The "L" shaped wall also has "L-Shaped" rebar, you do not want to cut through this, it's typically 1/2" (#4 bar) or 5/8" (#5 bar) in diameter. It's going to be at least 12" O.C. possibly tighter, and that means many more bars to cut.

Don't do it.

That tree will eventually push the foundation up just like a sidewalk, but instead of buckling you could face total failure of that section (and take the stairs out).

You would not plant a tree right next to your house would you?

Don't do it.

Let sleeping dogs lie.

A visual.........................

https://www.researchgate.net/figure/Cross-section-of-the-RCC-retaining-wall_fig1_267919476
https://www.researchgate.net/profile...ining-wall.png

It can be an "L" or it can be a upsidedown "T", same thing, it's all about the friction resisting lateral forces. The mass of the wall helps too, don't take mass out of the wall by putting a hole in it.

The only holes should be small weep-holes that allow water to pass though the wall and relieve pressure building up on the wrong side. Don't caulk weep-holes up if you ever paint the wall.

Thanks all! I think that George is right, though, now that it’s explained like that. There are tons of potential force on the wall when it rains, (and even when it doesn’t). I’m going to have to rethink my tree placement. :)

Can you build a box or something for it, or is that just mo problems?

Leave the wall alone and start digging downward to loosen up that soil.
The root system will try to go somewhere instead of into the hard pack layer, but downward will make it the most stable.

You're in a hot+dry+clay area so add vermiculite/perilite to retain water, peat to acidify/lighten/retain, and composted manure for nutrients and other modifiers.
(not sure of amounts etc)
Rent a powered post hole driller and have someone else go to town on it.

How about moving the planting location out from the wall another Couple of feet to clear the footing, and give it a clear shot into the ground.
Trees often need more space as they grow than it seems when they are planted.

Cheers Richard

Denis, my wife (retired Civil Eng) also recommends that you leave the footing intact and plant the tree further away from the retaining wall. The beauty of doing that is that you’ll have more room to pick the fruit off of the back side of the tree. SmileWavy

Thanks, Jim. That’s exactly what I’m going to do. Thanks all. :)

Probably a couple of feet isn't enough.

Ever hear the term "crown of a tree" or "tree crown"?

Much will vary with species and soil conditions, again I would not plant a tree any closer than I would near a house.

email: blogger@mocommunitytrees.org to comment « Basic Tree Care
http://www.mocommunitytrees.org/blog...-Not-Crown.jpg

http://www.mocommunitytrees.org/blog...ots-Spread.jpg

I am not an arborist or landscape architect but would consult one of those when in doubt.

Old rule of thumb of not planting closer than the crown or drip edge of where the mature tree is capable of growing to is an absolute minimum.

The illustrations I found on the Internet and posted above paint an even more conservative picture. One that doesn't even come close to working in urban conditions. Perhaps the species of urban trees found along city sidewalks have root systems designed not to spread out, but go down more.

In any case, you have to know where all of your underground utilities are before digging, and in some cases overhead lines.

In Michigan we have a state funded service called "Miss Dig", other states have something similar. I strongly suggest making the call, better safe than sorry.

If the "dwarf lemon" is a "Meyer" variety Lemon....they usually don't get much wider than 5 feet and much higher than 6 feet around here. Citrus in general don't have expansive or invasive root systems either - so they can be planted pretty close to walks or drives - or walls - although I am a usually a very conservative designer and always go out of my way to give my plants plenty of space.

That's the best in Vodka. ;)

Found this doing a search, a species people also put in pots.

https://www.fast-growing-trees.com/Meyer-Lemon-Tree.htm
http://forums.pelicanparts.com/uploa...1532273091.jpg

The best reason to give plenty of space between a plant/tree and a wall is not because of the root system.

It's so you have adequate access to both wall and plant/tree to conduct maintenance.

Walls need upkeep....plants/trees need upkeep.

Why have to squeeze yourself between wall and plant/tree to perform otherwise simple tasks. Especially a Citrus plant/tree that has THORNS!

Moving it away further from the wall was the proper decision. If nothing else, but for this reason.

It's the variety that everyone here wants and uses and so it's also the one with best availability.

Looking at the soil in Denis's photos....I have my doubts the tree will ever get much bigger than 4'. Maybe if he follows your pictorial on planting specs....and amends the soil with a good planting mix. And fertilizes. And waters. ;)

I foolishly ripped out a 'dwarf' lemon that simply went wild and produced literally well over 100 lemons at least 2wice a year. I wanted a more tame tree and have heard of the Meyer lemon. So, I went to the nursery and guess what? No citrus for sale anywhere because of a citrus quarantine.

Asian Citrus Psyllid and Huanglongbing in California

Wasn't Mavrik Aquaflow sold to contend with Psyllids?
Pricey........at $45/pint...as I recall. Maybe half pint.

Old article, LA Times. Maybe taken off the list for consumers.
.
Mavrik for Psyllids - latimes

It is a dwarf lemon tree that is supposedly going to grow to 8-10'. Even if a planted it on the edge of that concrete, it would have enough room to the wall and around it. I thought about the possibility of the roots just going under the "L" of the wall but the other problem is the hard clay soil. The latest plan is to raise the soil level in a gentle upward slope towards the wall and still plant it near the edge of the cement but above it in good soil.

We'll see, still researching. And I do have some soil conditioner for the clay plus a pick-axe to break it up.

Here's an option if don't mind building a frame around it. You could dig down to the footer depth and plant on top, as long as drainage was provided. Maybe drill some weep holes along the bottom with plastic screening inside to keep soil from washing out or plugging up your holes. Fill the entire thing with fresh new soil you bring in. Most nurseries sell a 'planter mix', which is what they use in re-potting their plant material. They get it in bulk and usually sell it either by the yard or bag. The stuff from HD would be more expensive and not as good but better than nothing if that's your only option.

https://www.thetreecenter.com/wp-con...ree-potted.jpg