"shade-tree mechanic", not in (some) dictionaries

[Laurence Horn]

Emmylou Harris's new album "All I Intended To Be" contains a
particularly fine song "Broken Down Man's Lament", which contains a
line I was sure I was mishearing, but it turns out I wasn't:

"I was a good shade-tree mechanic."

More fully, the quatrain in question runs as follows, confirmed by
both the enclosed lyrics and various web sites:

======================
I was a good shade-tree mechanic
So I sent myself to school
They smoothed out my rough edges
In my hand they put new tools
======================

No help from the usual sources, but urbandictionary.com comes through nicely:

A person willing to learn and perform scheduled maintenance or simple
repairs on their own vehicle rather than being completely reliant on
technicians who may be dishonest, careless, or ignorant.

14 thumbs up out of 14, not even counting Emmylou's.  Given the
context of the verse, this is clearly the intended sense.  Just out
of curiosity, I wonder how many "real" dictionaries would provide it.
(I assume DARE has the relevant entry under "shade"?  I don't have
the Volume IV, which encompasses "Sh".)

LH

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