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posted: 7/31/2011 5:12 AM

Art in the garden: Tall perennials add needed structure

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By Diana Stoll
The Planterís Palette

We've all heard about the importance of "good bones" in a garden, of using plants with lofty stature to define structure and form in a perennial border.

Large plants create a vertical profile in a landscape. They create silhouettes of leaves against sky in the landscape. Frequently, shrubs and small trees are chosen to accomplish this task, but don't forget about the structural qualities of herbaceous perennial giants.

Some gardeners shy away from tall perennials in their plans. They fear they will have to stake them to keep them from flopping about the garden. Certainly there are some high maintenance perennials in the four-foot-and-over category, but there are also plenty of beautiful tall plants built to withstand our tough northern Illinois storms. They remain defiantly upright with little intervention.

Another advantage to tall perennials is they generally bloom later in the mixed border because of their extra growth. They burst into bloom once their full height has been achieved and add color to the garden when it's needed most. And choices exist for both sunny and shady gardens.

Some of these structural perennials are most attractive when massed, while others can stand alone as specimens. In general, the more substantial and dense a large plant's form, the more likely it can succeed solo. Large perennials with open structures or lacy foliage usually look better as part of a grouping of several plants.

Some of the best structural perennials for full sun can be found in the ornamental grass group. Ranging in height from four to seven feet, grasses add height without bulk, swaying in the slightest breeze. Grasses in the Miscanthus family display attractive seed heads as the summer color palette fades for most perennials. Like grasses in the Miscanthus family, those in the Panicum family reach impressive heights, but if you want a grass that towers above the rest, choose either Miscanthus floridilus (Giant Chinese Silver Grass) or Erianthus ravenne (Plume Grass).

If you want to achieve an old-fashioned look, hollyhock varieties are a natural choice. Often exhibiting biennial tendencies, hollyhocks reliably reseed. The thick, almost woody stems of hollyhocks are strong enough to support their glorious flower display, rarely requiring staking.

The shrublike form of Boltonia is composed of fine-textured, blue-green foliage covered with an abundance of tiny, white daisylike flowers in late August. Another late bloomer is Eupatorium maculatum, or Joe Pye weed. Many cultivars are available, all with thick stems that stand straight without staking.

Heliopsis and Helianthus varieties are not only tall; they bloom a long time, too. They brighten the mid to late summer landscape with brilliant gold daisies. Rudbeckia "Herbstonne" is another sunny garden presence, soaring to nearly seven feet and covered with blossoms from mid summer to fall.

The bold blossoms of herbaceous hibiscus add a tropical flair to the garden. These shrubby plants are late to appear in the spring but quickly grow four to six feet tall. There are varieties available blooming with white, pink, red and lavender flowers.

Persicaria polymorpha, commonly called fleece flower, boasts plume-like flowers July through September. A single specimen of this perennial is a fine garden accent.

If you need tall perennials for a shady situation, check out Aruncus dioicus, or goatsbeard. It resembles an astilbe on steroids -- the same lacy foliage and fluffy flower spikes in exaggerated size.

If your shade garden has consistently moist soil, plant one of the beautiful varieties of Ligularia. The showy golden spires of The Rocket can reach as high as four feet. Or choose Filipendula "Venusta Magnifica." It has coarse leaves on robust stems that are topped with soft pink flower plumes.

I love Thalictrum rochebrunianum. Its foliage looks like an oversized columbine, and their flowers are small, sweet and lavender. Another meadow rue, Thalictrum flavum glaucum, has cool yellow-fringed flowers. These fine-textured plants look their best when they are planted in mass.

Consider using some of these big beauties in your perennial borders. The only thing larger than their stature is the burst of color they provide in your landscape.

•Diana Stoll is a horticulturist and the retail manager at The Planter's Palette, 28W571 Roosevelt Road, Winfield. Call (630) 293-1040 or visit