Can I plant Modesto Ash or Kurrajong/Bottle Tree over sewer line?

9 years ago

I live in the San Fernando Valley, in LA County. We currently have no street trees east of our house, and we want to put one there to help shade the house/yard. The County's pre-approved list for street trees includes only two choices for street trees: Modesto Ash or Bottle tree a/k/a Kurrajong (Brachychiton populneus), I think because they are relatively low-water. (We could seek a permit to put different trees on the street, but we want to go low-water anyway, and we like both of these trees.)

However, the sewer line runs from our house to the street east of us, under the area that is our first choice for planting a street tree. I think it's at least 5-6 feet deep (a few years back, we had an issue I think caused by a root from an Oak street tree on the south side of our house, and a contractor had to dig up the yard to access the sewer line, so I got some idea of its depth & location).

Some one told me that Modesto Ash trees are notorious for having invasive roots that disrupt sewer lines. But if the Bottle Tree grows into as large a tree as the Modesto Ash, wouldn't it have the same problem? I would think the laws of physics require a tree of a certain size to have a root system of a certain size to keep it from blowing over. Maybe both of these are problematic?

But then I've read some people saying sewer lines are sealed pretty well and it should not be a a problem to plant a tree over them if they are around 6 feet deep (though those writers were not specifically talking about the Modesto Ash or Bottle Tree). And we did have that prior problem with a root disrupting our sewer line...

Does it depend what the sewer line is made of? (e.g., concrete, poly-something plastic, etc.?) I don't know what ours are made of, but I could find out.

Ken

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Comments (3)

Toronado3800 Zone 6 St Louis
9 years ago
I would think a ten to fifteen foor tree would be the largest I'd try RIGHT on top of a sewer line even if it is a new PVC type. Why push your luck.
ken_adrian Adrian MI cold Z5
9 years ago
trees do NOT... can NOT.. invade modern chemically welded PVC pipes ...

they can very easily do so .. in old fashioned sewer lines.. like at the link

if yours were dug out... as you state.. i cant believe they do not modernize the pipe system ... perhaps you should be asking that contractor his opinion???

a very simple primer on tree roots... some say.. a root mass can be 2 or 3 times the size.. of what you see above ... but do NOT confuse yourself into thinking is is in the same shape ... most are pancake flat.. and only a few feet down in the soil [unless there is a leaking fertilizer source down there.. like a sewer pipe] .. see pic below on the root mass of a silver maple .. unless i forget .. lol .. almost all of its roots are there... in the space my ball cap took ... and the large ones going deep ... were headed towards a septic field... go figure on that ...

i dont know either of your trees.. but had green and white ash.. both tended toward surface roots ... which was a big problem for me .... i wnated them deeper ...

ken

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wisconsitom
9 years ago
Exactly as Ken has stated: If your sewer line is newish, and therefore PVC or similar non-porous, non-jointed material, no tree of any species is going to get in there. And also correct-tree roots grow out, not down. Yes I'm simplifying matters there, but that is the take-home lesson on tree roots.

If such utilities as sewer lines, water mains, etc. were truly vulnerable to tree root incursion, there would literally be no safe place to plant a tree. We know that's not the case-just look outside!-so therefore, it must (and is) acceptable to plant thusly.

I would NOT plant right over the top of a water shut-off valve. Those things need to be fiddled with eventually, and your tree will be right in the way. So give yourself some room there. Also, if there is a natural gas line, try to at least not plant right where the service line (to your house) veers off from the main. Same issue-eventually, that may have to be accessed. But really, from what I read, I strongly suspect you have room to plant on that east side.

+oM