OK cool, sometimes my imagination goes a bit wild (which can be quite fun!). I'm off to dump some more mulch on that hill now. Here's a couple of other new plantings where the hill is less steep. P sylvestris 'Nisbet's Gold'

and this Pinus strobus 'Niagara Falls' I'm planning on staking to a couple of stakes in a big X so the two leaders can grow outward a bit before the whole thing cascades like Niagara Falls. Or will that just create a sore crotch for the tree?

i tried the same type of brick wall ... and lost 3 different plants in it ... and all i could figure out.. was that it was south facing ... and winter sun was doing something wonky to the roots in winter ...

and my plants were much further back from the wall stone ...

removed the wall.. and never lost anything again ....

ken

I can see where having a 'bulge' created by blocks could possibly expose some of the root area to severe cold and even cause it to dry out faster than the rest. But in a z6, depending on the hardiness of the tree, cold should not be as big of a problem as it would be in colder zones. The dry part could be an issue no matter the zone.

Reversing the radius of the wall, cutting into the side hill, behind the tree, concave in shape, would create a flat platform for the tree to grow on and should make the entire issue less of a problem.

would possibly expose some of the root area to severe cold and even cause it to dry out faster than the rest.

==>> i actually speculated the opposite ... that the stone accumulated winter sun ....winter heat.. in the root zone ... perhaps the roots going in and out of dormancy ...

any sun at all.. and any exposed brick.. and a few hours later.. the whole wall melted the snow ....

btw.. i have a north facing brick wall ... and absolutely no problems ... and the prevailing NW winter winds doesnt have any impact ... this wall is one to 4 feet ...

ken

' i actually speculated the opposite ... that the stone accumulated winter sun ....winter heat.. in the root zone '

Probabaly that too. But I don't think that is the 'opposite' of what I said, it's just another variable in the equation.

The OP could take a 'wait n see' approach. His warmer climate and possibly warmer climate plants, may not be a problem.

I have no idea what the exposure of his hill side is or how much snow they get or if the ground freezes to any extent.

Hi Steve, I have no comments regarding the planting situation——I leave that to the experts.......but I love your tree selection! :-)

Yep, wait and see, live and learn at this point. It is a south facing hillside, but it gets shade in the winter from pine trees across the street. Some morning sun. That, being zone 6 and having clay soil I hope bails me out. Perhaps I could throw some burlap on top of the wall if I notice it melting the snow more quickly.

I was a little confused about the reversing the radius of the wall comment. But as I started to ask the question, I think I see what you mean. You mean digging into the hillside further back and continuing the circle of the wall higher up but using it to hold back the soil rather than holding the soil in. That way I could move the tree further back into better insulated soil. Perhaps a project for next year if I lose the tree.

' You mean digging into the hillside further back and continuing the circle of the wall higher up but using it to hold back the soil rather than holding the soil in. '

Yes, exactly, so things don't protrude but are embedded into the hillside. I know, a lot of work but my mind works that way :-)

To be honest, when we have winters here, with extreme cold and little snow, things can suffer, even die, depending on a lot of variables.

You're correct about clay soil, sand tends to heat up quickly and freeze/thaw faster so more chance of the root damage that ken talks about.

I never lived very long in a zone higher than z4 but I imagine z6 had shorter and much kinder winters than where I live. :-)