The Mixed Border is a bed thirty feet wide and twenty-three deep. Big. If plants are a foot at the front, they'll need to be ten, twelve, fifteen feet at the back. Some perennials are that big and more—check out my Helianthus verticillatus.
But across the back of the bed it's just as much about shrubs and trees. Here's a variegated ash—what a beauty—that is, at least for me, so slow-growing that you can only see it if you're standing at the back of the bed.
That's the giant Siberian filipendula in back of it, i.e., completely blocking the view of the ash from the front of the bed. This has since gotten moved to the Pink Borders—the fluffy clusters of flowers aren't really the pure white you see here; there's a hint, a contamination, of pink in then was too obvious to ignore. I've just planted in its place a, fittingly, Siberian perennial aralia that's supposed to get even bigger than the usual eight or ten feet. So the ash will still need to double in size to be part of the front-the-front show.
Meanwhile, the ash's performance is no less thrilling for being, so to speak, private. Click on the pictures—and then again—to see its full intensity as well as the wider context.
I always plant Russian Giant cannas nearby; on a good Summer they get ten feet tall too. Their immense purple banana-like foliage is a vivid contrast with the comparatively tiny white-and-green leaves of the ash.
If anyone nearby is in bloom as well—like the PG hydrangea at the immediate back, with unusually large flowers, called 'The Swan'—that's swell too. But the show is powerful even if there's not a flower in sight.
Get variegated ash from Greer Gardens, who says that the tree is "A fast grower, reaching 50’ in height and about 25’ in height." How lucky for them! I'll prune mine, someday, to keep it shorter than, oh, 15 feet. At this rate I've got another five years or so before I get out the stepladder and loppers.

What the? OK, a lot going on here. That's yellow-leaved forsythia for one, posted about here. And the big-leaved bamboo is posted here. But what is the white-leaved action in the center?
Those are the young leaves of my Silver Cloud redbud tree. They unfold before their chlorophyl even starts developing, looking somewhat like the translucent seek-pod disks of the "money plant", Lunaria annua. Well, in shape if not in coloring.
Chlorophyl does creep in—otherwise the Silver Cloud couldn't grow—but the leaves remain satisfyingly "whited" the whole season. This is still a young Cloud, but it's a (small) tree eventually. So it will shade both the bamboo and the forsythia someday. Notice that there are two pairs of horizontal wires in the picture. They are the bottom rungs of a series of wires strung up to ten feet high.
I'll gently flatten my Silver Cloud to them so it will be a Silver Disk or a Silver Slab floating with tidy serenity above the wilder duke-it-out of the forsythia and the bamboo. (Yes, I can hear your exhasperation: "Louis, can't you just let something grow?" Well, yes, I could, but I worry that then my garden could be confused with yours. (Ouch.))
And also, the frame those wires are attached to had to be there anyway: It's a stabilizing end section to my Belgian fence of beeches. (I'll post about those soon not to worry. And yup, I couldn't just let the beeches "grow" either.) Further, Silver Clouds welcome some shade, and this was about the only semi-shady spot I had left. And lastly because I never heard of espaliered redbud trees, let alone an espaliered Silver Cloud redbud. So of course I had to try it.
And—right!—someday this redbud tree will live up to its name and bloom. The flowers aren't red at all, even the buds. A hot lavender actually. Check out my video here. The buds emerge all along the trunks and limbs, not just from the tips of the branchlets. So espaliering a redbud should produce a singular floral effect too.
Stay tuned.