Finding worthy trees to collect in urban environments is just as difficult (if not more so) than finding worthy trees in the wild. The criteria is the same though – you are looking for trees which have been growing for a long time in an environment where they are repeatedly punished such that they develop the characteristics we are looking for in bonsai. It is therefore often helpful to first look for the environment. Once you’ve found that, finding the tree is easy (or easier).
I’ve noticed one particularly tough urban environment that is common in snowy climates: the perimeters of parking lots where massive piles of snow and ice accumulate after the snow plows come through. Any plants (particularly conifers) unlucky enough to be in a place where it is convenient to pile snow have a good chance of developing the characteristics we look for in yamadori.
Common species planted on these borders are tough, low-growing conifers like yews, junipers, and mugo pines. If you see something you like, act fast to get permission and dig. Often these parking lots are managed by contract landscapers who will rip out these ugly plants during the spring cleanup. I learned that the hard way this spring when a patch of mangled junipers I wanted to get at was replaced by some lilies as I procrastinated over approaching the landlord.
I was inspired to write this post because recently I dug a mugo pine from a very similar situation.