Wow Jeanne...things ARE looking good in your "shed" garden! Your tipsy buckets look so good...I need to move mine, they are getting too much shade where they are. LOVE the windmill and the million bells is HUGE and GORGEOUS! So many cool accessories..the galvanized containers and the wheel with the zinnias in it are great. What is the tall plant growing right next to your shed...the one with big leaves and tall stalks? Looks really cool! TFS~

Explain what a "symmetrical patterned grass border" is. What objective are you accomplishing by implementing that? Regardless of what you plant, 3' bed depth will hardly accommodate any real plants and their size. If the bed will be shallower in other places, I'd rethink that. You might include a picture of overall space for making the discussion more easily understood.

What a shame you have to give up 15 feet, but nice way you've decided to use it! First of all, to me that image looks like it's been cut-and-pasted together. I don't know where it is, but here in my zone 7, some of those things just wouldn't be blooming at the same time. And you certainly cannot expect to have perennials blooming all season long ... even a short one ... as they tend to bloom for only 4-6 weeks before going into a resting phase. You could do something like that with annuals, since they bloom all season long, but, of course, you'd have to replant every spring. When I was a child, our neighbor had an annual garden like that - snapadragons, zinnias, sunflowers, celosia, alyssum, and I can't remember what else, rioting along the back wall of their home. It was glorious. So that it doesn't look forlorn in the "off" seasons, you might consider a mixed shrub and perennial border, with some bulbs thrown in for good measure. Choose some great shrubs for the "bones" to give structure and interest to the border year 'round. Then start adding perennials and hardy bulbs, selecting them to give a succession of bloom from early spring through late fall. Be sure to consider leaf color and texture, as these will give interest to your garden even when not in flower, and can complement and highlight the ones that are in flower. Having lived in zone 7 all my life, I hesitate to make any suggestions for your zone, but would suggest there are numerous books and websites that can help, and the most helpful might be a visit to a local public garden to see what performs well and plays well together. Of course, taller plants in back, shorter ones toward the front, but try for lines that undulate in height and from front to back to avoid a stair-step look. FWIW, one of my borders, in half sun, has blooms from February through November with snowdrops (galanthus), daffodils, grape hyacinth, tulips, creeping phlox, perennial candytuft (ibiris sempervirens), tradescantia (which is wearing out its welcome with its spreading habit), peonies, irises, baptisia, roses, hardy geranium, cultivated daylilies (not hemerocallis fulva, the invasive orange "ditch lily"), false aster (kalimeris) 'Genghis Khan', garden phlox ('Davidii' and 'Franz Schubert', fairly resistant to powdery mildew), threadleaf coreopsis (either 'Zagreb' or 'Moonbeam' ... can't remember), nepeta, bee balm (monarda), obediant plant (physostegia) 'Miss Manners' (she reseeds less prolifically), New England aster 'Raydon's Favorite', Montauk daisy. There's a blue rug juniper for winter interest, two different flowering weigelas ('Wine & Roses' and 'Rubidor'), and at one end a mature redbud (cercis canadensis), at the other a passionflower vine (native passiflora incarnata) climbing the lamp post. Probably have left someone out ... sorry, guys. I will confess to also having a variegated euonymus (alien invasive ... days are numbered), just removed a Japanese spirea (another A.I., and it's neighbors responded with wonderful growth this spring), and a few years ago removed a red-leaf Japanese barberry (another A.I.). Where it wraps around into shade, the bed transitions into to shade plants ... but that's not what you need. That border did not happen all at once; it evolved over the years and, as you can tell, is still evolving ... Well, that's the whole point of gardening, isn't it? After all, I've heard it's been called the slowest of the performing arts.

@Yardvaark. Thank you. I never even thought of arranging the trees like this. I think this will be beautiful. I'd have to transplant the Japanese maple, and maybe one of my burning bushes. I cannot make the front (left of the bed any wider due to the fence gate, but I am going to widen the straight stretch to 6 feet and I am going to extend the flower bed so it curves around the garden shed. The front of the bed is large enough that If I remove the maple I'll be able to arrange Serviceberry as shown in your drawing.