Visitors are always surprised when they see my perennial border. The colors are lovely—mostly pastels, silvers, grays, and greens—but it’s not the colors that most people respond to. Rising like punctuation marks, spires and globes create a flow that both energizes and unifies the border.
Shape is the crucial element I keep in mind when choosing plants. A mass of perennials can look like just that: a mass. To create distinction, a border benefits from distinctive flower shapes. I look to globes and spires for long-lasting visual interest. From bud to flower to seed, these characteristic shapes last much longer than flower color alone. Their repetition and interplay bring excitement and energy to the garden.
While spires and globes are great individually, repeating these shapes unifies a garden bed. While one spire is an accent—think of a single columnar cedar—several create a theme. The eye takes in the series of similar shapes and passes over the rest of the plants as filler.
Spires and globes also give the garden a more architectural look. They work synergistically, playing off of each other’s different shapes to create tension within the bed and between each other. Surprisingly, this theme of two repeating shapes simplifies rather than complicates the border design.
Because I know the shapes will look wonderful together, I concentrate on getting the colors right by coordinating the bloom time of plants with colors that work well together. In spring, I pair the soft yellow spires of mountain false lupine with the globes of ‘Purple Sensation’ allium, while groups of ‘Lucy Ball’ allium globes set off the spires of ‘Trehane’ prostrate speedwell (Veronica prostrata ‘Trehane’, USDA Hardiness Zones 5–8). Midsummer is highlighted by the combination of the spires of violet-purple meadow sage (Salvia X sylvestris, Zones 5–9) and the globes of pink star allium (Allium stellerianum, Zones 3–8). Later, the theme is picked up by tall white Culver’s roots and the striking globes of ‘Taplow Blue’ globe thistle (Echinops bannaticus ‘Taplow Blue’, Zones 5–9). As the nights turn cooler, Japanese onion globes add sparkle to the pointy blooms of silvery lambs’ ears (Stachys byzantina, Zones 4–8). This border is particularly nice in autumn when the asters and mums join in with their related colors.
In a perennial border full of billowy color, soft outlines, and hazy fillers, it is important to have distinctive flower shapes. Whether you are fine-tuning an existing border or developing a new one, consider using globes and spires to create a memorable garden scene. The interplay between shapes can take border building to a whole new level.
Globes bring a bouncy feel to the border
I consider any spherical bloom to be a globe. Scattered groups create repetition and rhythm, lending a bouncy, playful feel to the border. My favorites are globe thistles and alliums. Globe thistles provide structure and height, and because alliums keep their shape from bud to seed head, they provide a long season of interest. Many drumstick alliums thrive in my Canadian Zone 2 garden, and I wouldn’t be without them.
‘Annabelle’ hydrangea (Hydrangea arborescens ‘Annabelle’), Zones 4–9, blooms white in late summer to fall, 3 feet tall
Blue-flowered garlic (Allium caeruleum), Zones 4–10, blooms bright blue in early summer, 2 feet tall
Chives (Allium schoenoprasum and cvs.), Zones 5–11, blooms deep purple–pink in summer, 2 feet tall
Common European globeflower (Trollius europaeus), Zones 5–8, blooms lemon yellow in early to midsummer, 2 feet tall
Drumstick primroses (Primula denticulata and cvs.), Zones 2–8, blooms white, pink, rose in midspring, 1 1/2 feet tall
Globe amaranths (Gomphrena spp. and cvs.), annual, blooms pink, purple, white, red in summer to fall, 1 to 2 feet tall
Globe thistles (Echinops bannaticus and cvs.), Zones 5–9, blooms bright blue in mid- to late summer, 1 1/2 to 4 feet tall
‘Lucy Ball’ allium (Allium ‘Lucy Ball’), Zones 3–8, blooms dark lilac in early summer, 3 feet tall
‘Purple Sensation’ allium (Allium ‘Purple Sensation’), Zones 4–9, blooms deep violet in summer, 3 feet tall
Stars of Persia (Allium cristophii), Zones 5–8, blooms pinkish purple in early summer, 2 feet tall
Twisted German garlic (Allium senescens ssp. montanum var. glaucum), Zones 4–10, blooms bright pink in mid- to late summer, 6 inches tall
Twisted-leaf garlic (Allium obliquum), Zones 3–8, blooms chartreuse-yellow in midsummer, 2 feet tall
‘Veitch’s Blue’ small globe thistle (Echinops ritro ‘Veitch’s Blue’), Zones 3–9, blooms blue in late summer, 3 feet tall
Spires add elegant stature
With their stately bearings, spires lend elegance to a border. The best ones are tough and reliable, like the speedwells, Culver’s roots, and mulleins. Speedwells come in an array of colors, and some have a bonus of silvery foliage. Culver’s roots are like speedwells on steroids; my all-time favorite is the tall white Culver’s root. Among the mulleins, dark mullein is the hardiest; it makes a forest of spikes with yellow or white flowers.
Anise hyssop (Agastache foeniculum), Zones 4–11, blooms violet-blue in mid- to late summer, 3 to 5 feet tall
Appalachian bugbane (Actaea rubifolia), Zones 4–8, blooms white in late summer, 1 to 4 feet tall
‘Bandera’ Rocky Mountain penstemon (Penstemon strictus ‘Bandera’), Zones 3–8, blooms bright purple in summer, 2 to 3 feet tall
Black cohosh (Actaea racemosa), Zones 3–8, blooms white in midsummer, 4 to 7 feet tall
Canadian burnet (Sanguisorba canadensis), Zones 3–8, blooms white in late summer to midfall, 3 to 6 feet tall
Dark mullein (Verbascum nigrum), Zones 3–8, blooms yellow in midsummer to early fall, 3 feet tall
‘Minuet’ spike speedwell (Veronica spicata ‘Minuet’), Zones 3–8, blooms pink in early to late summer, 1 to 2 feet tall
Mountain false lupine (Thermopsis montana), Zones 3–8, blooms yellow in early summer, 3 feet tall
‘Superba’ Chinese astilbe (Astilbe chinensis var. tacquetii ‘Superba’), Zones 4–8, blooms violet-rose in late summer, 4 feet tall
‘The Rocket’ ligularia (Ligularia stenocephala ‘The Rocket’), Zones 4–8, blooms yellow in early to late summer, 6 feet tall
White Culver’s root (Veronicastrum virginicum f. album), Zones 4–8, blooms white in midsummer to early fall, 6 feet tall
‘White Giant’ long-leaf speedwell (Veronica longifolia ‘White Giant’), Zones 4–8, blooms white in late summer to early fall, 4 feet tall
‘White Icicle’ spike speedwell (Veronica spicata ‘White Icicle’), Zones 3–8, blooms white in early to late summer, 1 to 2 feet tall