This is sensible for perennials since each is in flower for only 2 to 4 weeks. We can extend bloom time for some by removing spent flowers -- deadheading -- but it's smarter to rely on the plant's non-flowering qualities to carry the load.
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Here's how-to, using four plants which combine well because between them they have a variety of features that provide favorable contrasts:
All are long-blooming, do so at varied times of year or offer multiple seasons of interest. So even when none of the four is blooming, there's visual interest in the garden through contrast in shapes, textures and foliage colors.
In love with flowers? To this solid combination we might add one or two plants that are glorious in bloom but a bit shabby afterward -- daffodils or columbine (Aquilegia) come to mind. When the initial group exhibits good form, texture and foliage color it can make up for other plants' slack time.
Few plants take charge in a garden like peonies do.
Many of the hybrids between tree peony and herbaceous peony fit the bill. These intersectional hybrids (such as the 'Itoh' types) have great bloom, healthy clean foliage, and at least a fair record of significant fall color. In more traditional peonies, we keep a look-out for the rare varieties that provide all three features. One is a late blooming single white flowered 'Krinkled White;' it can be a showy yellow in autumn. Another is an early double pink, 'Estafette,' which can develop burgundy tones in fall.
"Coarse" and "fine" describe the pattern that light creates on the plant surface. Plants with substantial leaves or crisply variegated edges tend to be visually segmented into large blocks because of the leaf edges and the leaves' bold shadows. Plants with smaller leaves or ferny small parts have less pattern, and so look more solid. Below, from most coarse on the left to finest on the right. (Read it: Lenten rose/ Helleborus offers a further lesson in texture.)
Its foliage is large, but entirely basal so it's completely hidden from bloom time until fall by flowering stems which create a dense, fine dome. This is a relative of statice, described in bloom as "a lilac-pink baby's breath." We often pair it with a coarse foliage plant such as peony, or something of a different shape such as columnar gayfeather (Liatris spicata).
Ornamental mulleins are underused. They're great for sunny dry places and foliage effect. We add their gray-green large leaves to this group for contrast. The spike form flowers are an additional accent, but only for a few weeks.
With perennials, it's best to accept the reality of spent blooms. Either look the other way as they go brown, or step in and clip them off in time to promote a second flush of flower.
A dwarf such as Buddleia 'Nanho' is the right size (5' rather than its species 6-10') for most perennial combinations. There are even smaller selections, such as the 36-inch 'Lo and Behold' series in blue-violet, lilac, white and purple, and the 'Flutterby Petite' series that includes the best blue we've seen in 'Blue Heaven.' When we add the gray green spreading arms of butterfly bush to a peony-mullein-sea lavender combo, we seal the deal on drama right through summer. There will always be a pleasing contrast between one or more of the plants. As a bonus, the butterfly bush brings bloom and the delightful presence of butterflies and hummingbirds in late summer.
Some other plants in this bed: Boxwood 'Winter Gem', variegated Liriope, lungwort (Pulmonaria), false indigo (Baptisia australis), oakleaf Hydrangea (H. quercifolia), big betony (Stachys micrantha).
Flower is fleeting even on the longest-blooming perennial such as threadleaf coreopsis. Even if a plant's in flower for six weeks, it must occupy its space pre- and post bloom for 3 or 4 times as long each year.
So if we rely on flower or use plants with big blooms that age to big brown, cutting is important. Fortunately, it's simple to do. Look for brown, cut it down!
It's tough to maintain a single focal point in a garden full of constantly changing plants. Yet gardens need that kind of direction to keep the eye happy. We often position a bird bath, bench, arbor or path among the plants as a focal point.
Take a look here as we use a path as a focal point, framing it with non-plant features (tree trunk sculpture and bench).
King Creek Timber Products in Linden, Michigan harvests these gall-affected spruces and cedars as complete trunks, strips the bark and seasons the wood like fine lumber. Homestead Timbers in Mame, Michigan has whole tree logs, too.
Metal sculpting studios such as Bad Axe Ironworks in Bad Axe, Michigan and Altra Design in Huntington, Indiana make the tree-like trellises you see here.