• Ongoing coronavirus / COVID-19 discussion: how is the pandemic affecting your community, workplace, and wellness? 🦠

    Working from home? So are we. Come join us! Cyburbia is a friendly big tent, where we share our experiences and thoughts about urban planning practice, planning adjacent topics, and whatever else comes to mind. No ads, no spam, no social distancing.

Landscaping Tree Pit Size?

michaelskis

Cyburbian
Messages
20,440
Points
53
We are in the process of reviewing some details in our Standard Specifications Manual, and I was wondering what size everyone uses for their tree pits in the downtown core area. Our PW director says that he needs to top the trees because our pits are too small. I am not so sure. Any information and links would be greatly appreciated!
 

Gedunker

Moderating
Staff member
Moderator
Messages
11,681
Points
44
We use 4’x4’ as the standard in our central business district. Our walks are 13’ wide, so there’s a comfortable 9’ remainder, plenty wide for ADA access. We also spec trees that will be comfortable in a tree well that size, and that tend to set deep roots rather than horizontal roots systems.
 
Messages
2,873
Points
23
Our PW director says that he needs to top the trees because our pits are too small. I am not so sure.

You are correct to question whether the trees should be topped off, especially for the reason given: "pits are too small". That is outdated thinking from the 20th century; it is no longer scientifically supported by arborists with professional and/or academic credentials.

The "21st century" thinking:
If the pits are too small for new trees you're thinking of planting, then get different species of trees. The new trees might be either:
(1) Smaller and/or narrower when they are "adults", or
(2) Of species that have much deeper tap roots - and fewer flat (or "horizontal" or "lateral") roots.

Gedunker alluded to (1) and wrote about (2):
... . . We also spec trees that will be comfortable in a tree well that size, and that tend to set deep roots rather than horizontal roots systems.

A diagram might be useful: that is, look for tree types that have the 1st tree's root system, and avoid tree types with the 3rd tree's root system.
3_Root_Systems.jpg


BTW- "Tap Root" is an official term used by arborists.
("Net Roots" and "Flat Roots" are more informal lingo.)

Useful tip: It's helpful to familiarize yourself with the role the Tap Root plays.
 

DVD

Cyburbian
Messages
15,367
Points
53
Most of our stuff is desert planting so we get a lot of the tap root style trees. Minimum area for a tree is 5' wide. The actual hole for the planting is whatever the box size is. We require a 3" caliper tree which I believe translates to a 48" box.
 
Messages
2,873
Points
23
I'd be worried if my public works director was using the term "tree topping". That clearly demonstrates that someone has no idea of tree care and maintenance.
Alternative scenario:
The PW director knows a lot about tree care and maintenance, BUT.........
PW is being rewarded on short-term results only.

Topping gives you a brand new growth of leaves in the fastest possible way. PWs can time this for when they are being evaluated.
This would be a classic example of management "rewarding A, while hoping for B".
This scenario is assuming that the PW director probably would not be around long enough to face the consequences of an annually topped tree:
Topped_Tree.jpg

Caption: This tree had annual "toppings" for a few years in a row, and is now dying or mostly-dead.
 
Top