I always plant tree in native soil. The roots will have to grow out into some day, anyway. If it's really horrible, like your clay, that's good advice to dig the hole much, much wider. Once you've busted up the clay and put it back in the hole, it should be a lot easier for the roots to move through.
We are on the cusp of hydrangea season here. The 'Endless Summer' has already colored up. I'm sure those rebloomers were designed for you guys in cold climates. Since it blooms on old & new wood, if the bush gets frozen to the ground and loses its old wood, you still have a shot at blooms.
I'm going to upload photos of the ultimate mophead hydrangea (my opinion) on my page. It's called 'Ayesha'. Grows and establishes much faster than all others (possible choice for difficult soils?), has a darker, shinier leaf and the petals are cupped so that some people call it the popcorn hydrangea. You will love it if you can find it.
I will find out tomorrow, if I don't have a tag on one I will ask my friend at the greenhouse where I bought them. Might not be till Monday cause tomorrow is mothers day and she will be swamped. They are purple with feathery / lacey leaves and there are 2 types, one that flowers and one that doesn't. I have seen some in hubby's landscape magazines advertised as the "new japanese maple". They grow very fast too, I cut mine back every fall. It is growing in **** clayish type soil that hubby hauled in to put around the pond. My friend always tells her customers to dig the hole twice as big as the root ball & you could work in some sand or something to fill in around the root ball.
Tippy, My elderberry does not get berries. It is ornamental. They are inexpensive too, I'll snap a pic tomorrow and post it.
GSD
Yes, that is what I will put there--a Elderberry Bush or two. I googled it and looks like it will do well there. We feed the birds and I plant flowers, shrubs to attract them, and birds love the Elderberry Bush, although birds and berries make for a big mess. Will just have to hose everything down every other day for the blue stains on the patio, gazebo and everywhere.
Oops --Husband just said no Elderberry bush or tree, as he will be the one cleaning up the big mess. Aaaaw he knows me well--" Honey, please.... "
Casper
The Dahlias are kept in the basement and its cool down there in the winter. I'm worried about you and please let us know what they do this week. Your one cool, calm and collected girl. Wish I had one tenth of your calmness.
I put them in the garage that is not heated but it is not freezing. They, the cannas, actually did come back when I planted them in the ground and that does freeze around here LOL.
Not a water issue. Down here we lose stuff because the combo of high humidity and heat lets fungal diseases attack much worse. We try to cheat but some things are just not meant to be.
Are you hanging the dahlias and cannas in an area above freezing? It's hard to put them someplace that is both cold but not freezing and not getting dried out by your heating system.