I mentioned the supposedly superior cold hardiness of Korean Stewartia to the Dulith, MN-based nurseryman I bought my S. pseudocamellia. I suspect he had heard this before, and he became almost agitated when I mentioned it. I have no idea if one is hardier than the other, but they are both hardy in z4. Mine has seen -25F a few times. It survived the infamous 2013-‘14 winter with no visible damage whatsoever, but flowering was very sparse that season.

Failed trees and shrubs pulled out of amended holes have circling roots because they were planted with circling roots in the first place, did not do well enough after planting to grow much beyond the amended area. Roots always grow away from the center of the plant, seek fresh ground unless the plant is so weak or the roots encounter a barrier (such as a pot wall) so strong that they are deflected. The start of unamended soil around an amended planting hole is not enough of a barrier to deflect roots. The main problem with amending of planting holes is how it affects the movement of water into and out of the hole. You want the same soil texture throughout the rooting area of the plant. Small plants like alpines can comparatively easily be provided with a special soil created by digging in and mulching with rock products. Ephemeral plants like annual flowers and vegetables can have organic material dug into their beds without it requiring a big area to cover the full extent of their root growth. And these often respond to high levels of organic material. With plants that are replaced every year it is possible to re-amend their growing area every year. With longer term plants this is not possible, these have to grow in soil that is managed without frequent amending. Amendments dug in before planting break down over time and allow the soil to return to same organic levels it had before planting, making it pointless to amend the soil at/before planting.

I'm a big fan of sugar maple. Compared to Red Maple I consider it to have superior and more natural fall color, to be longer lived, less tolerant of ridiculous amounts of water and less tolerant of road salt. If size is of ultimate concern they can grow into larger trees. There are other maple varieties which stay in the range you mentioned.. Paperbark and Shantung are two currently on my mind. I'm also a fan of nyssa sylvatica (usually called black gum). They're somewhat difficult to transplant and slower growing in my limited experience, but have GREAT fall color, and are sound trees. There is even a water loving version.

I don't necessarily agree with taking out the maple tree. For me it depends on the variety. I have a sugar maple that I would never consider removing. It is a beautiful tree with great fall color. It casts quite dense shade, but I do grow hostas and other shade tolerant plants under it. What I've learned from others is to water and fertilize the whole area, not just the hostas. If you start with a large planting hole and a good-sized plant, it will compete successfully with the tree roots if given enough water. On the other hand, if the tree is a silver maple I would not hesitate to take it out, the sooner the better. The roots of silver maples actively seek water and the tree's wood is soft. It has no redeeming value. Mark