Best time to plant trees in Zone 5 and North is Spring. Fall is generally second best, but now is a bit late for Zone 4. (I've had good luck planting trees as late as Thanksgiving in Zone 6).

Don't assume that what the commercial landscapers do is the best thing. The city may be influenced by budget concerns and when landscapers have the free time.

But yes, many nurseries shut down long before the end of Fall landscaping season. I've run into this problem. I try to turn my lemons into lemonade by shopping for trees on clearance in the Fall. I look through the Lowes bargain bin and shop at end of season sales at a local native nursery. This works better for some things then others. Great time to buy something common and deciduous. If you want something specific, Spring is probably better.

i used to buy plants all summer long ... and hold them over until the fall planting period in my MI ...

i would hold them in bright shade.. so black pots would not heat the roots in sun ...

z5 is highly divergent.. in my ground freeze area... most things.. but for oaks.. can be planted in fall ... and then ground freeze holds them in suspended animation until spring ...

in spring.. plant so that there is 6 to 8 weeks of dormancy.. root growth.. before the heat of summer hits ... which for me.. was basically april ... [getting into may.. with the stuff you cant kill] .. which is just as problematic ... as nobody is selling anything until later may .. whats that all about ...

ken

And never assume that municipal landscapers follow the best practices! They, as well as the commercial companies may do things at the wrong time of year just because their employees are not mowing any more and snow removal hasn't started yet.

Where in Ontario? Now through November can be an excellent time to plant trees in this area (southeast MI), depending on a number of factors (species, site conditions, type of stock - B&B or potted). What kind of trees is your town planting? Are the trees B&B?

And yes, the selection at retail outlets is often limited in the fall.

A problem with fall clearance items can be that they may have been sitting at outlets deteriorating since spring. For optimum results fall planting needs to be done before roots have elongated. This happens after winter stem buds have matured, which if the top of a particular specimen has quit growing comparatively early due to drought for instance might at this point have actually happened a few months ago - autumnal root growth is not prevented by summer soil conditions including drought. Autumn in this context is as much or more a physical state of the plant as it is a time of year.

Our fall planting-quite extensive-consists of trees just harvested from nurseries, heeled in our holding facility. Fall is hands-down one of the primary planting times. This is zone 5. Fall has always been a good time to plant in zone 5. It is species-dependent, nothing more and nothing less. So, Freeman maples don't do well when fall-planted. Likewise, any fleshy-rooted species we wait until spring. But fall is equivalent to spring as a time to plant trees in zone 5.

It sounds like you're talking about dormant bare-root stock. Taking full advantage of the superiority of fall planting requires use of containerized stock with intact root systems. Which of course can often be hard to accomplish even when container stock is available due to the common deforming of roots by commercial sources keeping plants in the same sized pots too long. In those instances it is more important to correct root deformities than to get maximum extension of existing roots at planting time.

I'd agree w/bboy on this point -- the more the root system would be damaged by transplanting, the less desirable a fall transplant would be. If there would be no/minimal damage, a fall transplant would be fine.

Bare-root stock is minimally disturbed. Likely quite a bit less than hacking and beating a decent root system out of a potted tree. Dormancy in this case does relate to leaf senescence but I would not doubt pure expediency creeps into the mix, with field conditions probably ruling all. We don't do this to fail however, and your abstract musings conflict with the reality I've seen for years.

I planted a 6 foot potted Japanese 'Garden Glory' full moon maple at the end of December, 2014 - it survived, and thrived. That time of year was unseasonably warm - the deep freeze occurred a few weeks after that. Actually, I was relatively new to tree planting at the time. so it helped convert me to the fact that, at least for my micro-climate, I can get away with quite late fall planting. Plus the fact that my major tree nursery had reduced ALL stock between 70% and 90% - and there quite a few bonanzas in there - helped get rid of any trepidation I may have felt!

There's that-your good price points on these plants tending to shield you from any failure effects. I'd say too that species matters. Some will work better than others in a fall planting.