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‘Dark Knight’by George Papadelis

When fall approaches, many gardeners believe it’s time to hang up the trowel and bring an end to another growing season. Fall, however, offers us many opportunities to enhance our landscape. Most plants allocate their energy to developing strong root systems in the late season. This, along with the cooler, less stressful growing conditions, makes fall an ideal time to plant. Cooler weather also means more comfortable temperatures for garden “work.” The ever-expanding palette of late-season annuals like flowering kale, flowering cabbage, dianthus, dahlias, petunias, verbenas, and so many more are increasingly available to brighten flowerless voids and refurbish tired window boxes. Let’s not forget pansies and bulbs. Fall-planted pansies will often bloom until the holidays and then begin blooming again early next spring.

Jonathon Hofley / Michigan Gardener
‘Worcester Gold’Besides the popular garden mum, there is also an enormous selection of late-season perennials that are often underused. The list of shade lovers includes anemones, toad lilies (Tricyrtus), perennial lobelia, snakeroot (Actaea or Cimicifuga), yellow wax bells (Kirengeshoma), certain hostas, and many, many more. The list of late-season bloomers for sunny locations is even longer and includes blue mist spirea (Caryopteris), a reliable performer and a beautiful addition to the autumn landscape.

Most blue mist spireas grow about 2 to 3 feet tall and wide, and have powdery blue flowers. Tight, one-inch clusters of tiny blue flowers develop in profusion along woody stems. Flowering lasts from mid-August well into October. The fragrant foliage of the more common varieties is a silvery blue-green, but others may be gold or green and white variegated. They thrive in any well-drained soil and prefer full to part sun. They flower on new wood, so pruning the plant in early spring to about 6 inches should yield excellent results.

Most plants that are referred to as “perennials” have stems that die down to the ground every winter. Blue mist spirea, however, is like lavender, butterfly bush (Buddleia), roses, and Russian sage (Perovskia); it develops woody stems that, to at least some extent, stay alive through the winter. In a severe winter, these stems can suffer, but a few inches of soil mounded directly over the plant’s crown in late November will insulate it. This discourages severe temperature fluctuations and reduces damage from drying winds. In spring, simply remove the soil from the plant’s base. When the new growth becomes apparent, prune away the dead stems. Additional pruning may be necessary to shape the plant and/or control its size. This same technique works well for roses, butterfly bush, Russian sage, lavender, and other vulnerable woody plants.

Eric Hofley / Michigan Gardener
‘Dark Knight’Blue mist spirea is usually propagated by rooting soft tip cuttings. Some gardeners, however, will be rewarded with seedlings that develop at the base of the plant. Pollinated flowers will produce seed that is very viable but also variable. When these grow to a few inches tall, they can be transplanted to a permanent location and evaluated for potential future use.

Two readily available varieties are ‘Longwood Blue,’ with light blue flowers and gray-green leaves on plants that grow about 3 feet tall, and  ‘Dark Knight,’ which boasts similar but deeper blue flowers on slightly taller plants.

Jonathon Hofley / Michigan Gardener
‘Worcester Gold’For beautiful golden foliage, ‘Worcester Gold’ is wonderful from spring until fall. It also has blue flowers in August and September on 3-foot tall plants. A newer gold cultivar called ‘Sunshine Blue’ has even more intensely gold foliage on 3-foot tall plants. Its amethyst blue flowers in August and September glow against its attractive foliage.

‘Snow Fairy’ is the first variegated leaf selection. It has brightly variegated green and white foliage that alone warrants the use of this plant. It produces clear blue flowers, and grows taller, to about 4 feet. Two new blue varieties include ‘Grand Blue,’ with dark blue flowers above dark green leaves on plants that only grow 2 feet tall and wide, and ‘First Choice,’ which produces rich, cobalt blue flowers on a more freely branching, compact plant that is just less than 3 feet tall.

Companion plants

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‘Longwood Blue’The flowers of blue mist spirea make a wonderful companion to other late season perennials and annuals. Most ornamental grasses are at their peak in September and may offer a perfect backdrop. Switch grass (Panicum) has erect, green to blue-gray stems and leaves topped by sprays of burnished bronze seedpods. Several varieties offer heights ranging from 3 to 7 feet tall, but ‘Shenandoah’ or ‘Heavy Metal’ would be the best Caryopteris partners. Shorter maiden grass (Miscanthus) like ‘Adagio’ and ‘Little Nicky’ offer silvery or pink flower plumes that blow in the wind. Feather reed grass (Calamagrostis) like ‘Karl Foerster’ offers stiff, wheat-colored plumes in June that last for almost a year on 4- to 5-foot tall plants. Fountain grass (Pennisetum) grows about 3 feet tall and produces fluffy, bottlebrush flowers of burgundy, beige, or black. All of these ornamental grasses are outstanding perennials to grow with a blue mist spirea. More importantly, each fall, ornamental grasses leave behind beautiful faded plants that last throughout the winter. These tan mounds of leaves and flowers provide even more interest when sprinkled with fresh snow or covered in glistening ice.

For a flowering blue mist spirea companion, you have many choices. Mums and fall-blooming asters come in an enormous color range and grow as low as 12 inches to as tall as 3 or 4 feet. The gold to orange flowers of Helen’s flower (Helenium) stand atop erect plants growing 3 to 4 feet tall. The goldenrod (Solidago) cultivar ‘Fireworks’ offers airy sprays of tiny yellow flowers that last throughout September. Windflower (Anemone) will thrive in sun or shade and produces masses of pink or white flowers to accent your blue mist spirea blooms.

Autumn is a great opportunity to spruce up flowerbeds and begin planning for next year’s garden. Plant some spring-blooming bulbs, think about trying some pansies, and don’t forget those mums. With these and the myriad of fall bloomers, all of us should have a spectacular September garden. A plant like blue mist spirea adds some excitement to our palette of late-season choices.

George Papadelis is the owner of Telly’s Greenhouse in Troy, MI.

At a glance: Blue mist spirea, bluebeard

Botanical name: Caryopteris (ca-ree-OP-tur-iss)

Plant type:Perennial

Plant size:2-4 feet tall and wide

Habit:Rounded bush

Hardiness:Zone 5

Flower color:Various shades of blue, from light to dark

Flower size:1-inch clusters

Bloom period:Late summer to fall

Leaf color:Gray-green, gold, white & green variegated

Light:Sun to partial sun

Soil:Well-drained

Uses:Perennial border

Companion plants:Medium-sized ornamental grasses, late-blooming perennials such as Helen’s flower, goldenrod, windflowers 

Remarks:Stems dieback depending on the severity of the winter (similar to Russian sage and butterfly bush). Blooms on new wood, so prune in early spring.