there is no issue here ... just do it ... i am glad you thought about it as a variable.. now dismiss it ... no transplant is going to out compete some huge old tree for anything ...

some peeps say a tree can have a root mass.. twice as big.. as the tree you see above ... and when you think of it that way.. your piddly little transplant will not effect the monster in any way ....

your only problem.. is insuring that the TRANSPLANT .. any transplant ... of any kind ... gets enough water until it is established ...

see link for planting guide ..

NEVER fert the transplant... or the monster will grow roots into the transplant.. and MIGHT choke it out ...

ken

Here is a link that might be useful: link

Visual scale set by Liriodendron will make a dwarf conifer look out of place. And it will drop debris into the spruce. Look for another area, not dominated by a tall deciduous tree. Or choose a more normal looking shrub, that is not a dwarf "nest" that evokes the high mountains.

I should add there are some other shrubs near the base of the tree, a rhody and mountain laurel, which are doing fine. Presumably their roots are shallow enough. The little conifer looks nice with these plants nearby.

Plant it how ever you want. its your yard.
Im sure it will look very nice.

I agree with bboy.
You can do anything you want, but it's out of scale design wise. The two plants do not belong together, whether they can grow successfully side by side doesn't matter. It's just basically 'wrong', beyond just a matter of taste.
Developing a sense of scale can go a long way in designing a garden that looks like it has a cohesive look rather than one that looks like it has no guiding hand.
Mike

I have a tulip tree in my small suburban yard. I don't 'see' it, except the trunk when I look at my garden. So I wouldn't worry about the composition with the tree and a garden planted underneath. If you have good enough sun in the spot, I would plant it. The challenge would be keeping the garden under the tree watered without inviting tree root competition. I try to water a big area - the whole garden area rather than 1 individual plant and choose plants that like it on the dry side. Conifers should be okay once established.