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Asclepias incarnata (photo by Maxal Tamor)

When the dog days hit, our gardens often take a turn for the worse.

But late-blooming flowers can liven up the landscape just as everything else turns dull.

By Panayoti Kelaidis

Mid-to-late summer is the most predictable time of year for warm weather and lovely evenings. Surely you could use some durable color to accompany the cocktails, the barbecues and the beautiful half-light that spreads coolness over the summer landscape as the shadows of the Flatirons trickle their way eastward in the lavender twilight.

A wealth of late-summer flowers is available for our gardens—and not just plants in the mint and daisy families (although these two groups have done an especially good job of brightening the last half of the growing season). I value not only color in late summer, but the many fragrant plants that perfume the evening air and attract a wealth of interesting insects. I love a diversity of buzzing, humming and swarming insects in the garden not just to attract birds, but for their own delightful, buggy selves. I hate walking through the “horticultural” section of big-box stores that are stacked with endless insecticides and pesticides. Use them minimally, if at all. A diverse garden full of all manner of beneficial insects is the best defense your plants have in the long run.

Here are my picks for plants that perk up the late-summer landscape. Plant a few in your yard, and you too will rejoice come the dog days of summer.
summer-surprises-Asclepias-incarnata-Photo-by-Maxal-Tamor
Asclepias-incarnata. (Photo by Maxal Tamor)

Asclepias incarnata, or swamp milkweed, is enjoying a huge resurgence in popularity because it’s the prime host plant for monarch butterfly larvae. Although monarchs aren’t common here, they do occur, and growing any milkweed is bound to increase your chance of attracting these glorious insects. Alas, many milkweeds merit the “weed” suffix, as they can be terribly invasive in gardens. This species is widely distributed in the eastern United States and also happens to be native to Boulder County. The wild forms are relatively uniform pale pinks, but a wide range of colors is available in cultivation. This rarely grown native makes a fabulous show in late summer, with big clusters of white or pink flowers. Although most often found near swamps or streams in nature, milkweed grows well in ordinary garden conditions.

Allium senescens (photo by Panayoti Kelaidis)
Allium senescens (photo by Panayoti Kelaidis)

Allium senescens suffers from several handicaps, beginning with its name—there is nothing senescent about this plant. It’s sprightly, vigorous and youthful. And many forms are in cultivation. Seek out ‘Glaucum’ or ‘Blue Eddy’, which are especially blue in the foliage and often have showier flowers. Although it can be sold as a bulb, this plant is also sold as a perennial, so look for it in the summer months as well. What makes this onion so special is its wonderful foliage—a terrific whirlpool of attractive, swirling leaves. And it blooms unusually late for an onion, often in August or September, when the garden can use some spice. What’s in a name? Quite a bit, if it’s a lovely onion like this.

Allium-Millenium (photo by Panayoti Kelaidis)
Allium-Millenium (photo by Panayoti Kelaidis)

Allium ‘Millennium’ is a hybrid of several Asian onions that possesses unique traits. First, it’s sterile so you don’t have to worry about its seeding around the garden. And it’s vigorous without spreading too widely. It quickly makes a clump a foot or so across and then settles in. The big drumstick-size flowers are 1- to 2-feet high (depending on moisture and nutrients) and a vivid purple blue. The flowers completely cover the attractive foliage for weeks on end in summer. This plant can endure long periods of drought, but does repay a good watering in dry spells, as it builds up to bloom with a more lavish show. My friend Mark McDonough bred this plant and named it in 2000. It’s quickly become a garden classic sold by many nurseries.

Japanese anemone (photo by Ralf Neumann)
Japanese anemone (photo by Ralf Neumann)

Anemone japonica is an incredibly showy, long-blooming and rewarding perennial that is rarely seen in local gardens. One caution to beginning gardeners: The “Japanese” anemones actually include a number of different and highly variable plants that grow throughout China as well. Anemone hupehensis is perhaps the biggest offender. Superficially like a Japanese anemone, this husky, hairy plant can spread rather quickly and become a problem in an intimate garden. Not technically xeriscape plants, anemones tolerate drought better than many classic perennials. Seek out the smoother-leaved clumping cultivars like ‘Queen Charlotte’ or the double forms that don’t spread quickly at the root. These form graceful mounds of attractive foliage and in late summer, the tall and sometimes VERY tall stems (5 feet or more!) branch gracefully and produce plump, balloon-like buds and gloriously waxy five-sepal or double flowers. The flowers are somewhat asymmetrical in a very pleasing way. Shorter cultivars for smaller gardens are available, and most gardens have a spot where an anemone can perform its elaborate kabuki dance in fall.

Aster novae-angliae (photo by Panayoti Kelaidis)
Aster novae-angliae (photo by Panayoti Kelaidis)

Aster novae-angliae is also known as the New England aster. But in England it’s called the Michaelmas daisy, and you’ll find it in every classic English border across the pond. I’m astonished that such a spectacular garden perennial is rarely seen in our gardens. It does need some irrigation to do its utmost, but does not need or like it wet. This aster makes an upright mound of neat foliage and a veritable dome of brilliant deep-violet, blue, pink or white flowers. It can self-sow modestly, but the resulting plants are easily removed or shared. The cultivars ‘Purple Dome’ and ‘Hella Lacy’ are vivid purple pinks and well worth seeking out. But give me the classic wild form and I’m happy!

Eriogonum allenii (Photo by Panayoti Kelaidis)
Eriogonum allenii (Photo by Panayoti Kelaidis)

Eriogonum allenii is among the most abundant, widespread and glorious of western wildflowers. A few species have managed to edge their way into cultivation—especially the common sulfur flower (E. umbellatum), thanks to Plant Select. It’s worth seeking out the Shale Barrens buckwheat (E. allenii)—one of the few species that grows in the eastern United States. It hails from the Appalachians, but this buckwheat grows vigorously in Colorado and makes mounds of evergreen leaves that are wonderful in their own right, especially in late summer when they take on orange and bronze tones. The stems rise 15 to 24 inches (depending on moisture and sun), and the flowers form a dome of brilliant yellow gold for months in late summer. By autumn, they transform into a reddish-orange hue that is even more striking. I consider this one of the most rewarding perennials I’ve ever grown.

Eryngium giganteum (photo by Panayoti Kelaidis)
Eryngium giganteum (photo by Panayoti Kelaidis)

Eryngium giganteum is a remarkable plant in the carrot family. This intriguing plant is beloved by many, but most especially by Ellen Willmott—possibly the most lavish gardener who ever lived. For decades in the late Victorian and Edwardian era in England, Miss Willmott indulged in the wildest horticultural fantasies any plutocrat could fathom. She employed hundreds of gardeners, grew millions of plants and dazzled the gardening world with her prowess. Books have been written about this remarkable woman, but her greatest memorial will likely be Eryngium giganteum’s common name—Miss Willmott’s Ghost. And who could resist having Miss Willmott’s Ghost haunt their garden? The plant takes a year or two to bloom and then dies, but it produces many self-sown seedlings and will persist forever in most gardens. The stems can climb to nearly 3 feet (but usually 2) in rich soil—and the enormous, white, ghostly flowers bloom from midsummer to fall. If cut and dried upside down, the flowers make everlasting bouquets. I’ve let this ghost run rampant through my borders—you can’t really have enough of it! Miss Willmott was so fond of it, she’s believed to have surreptitiously scattered seeds of it in any garden she visited. A year or so later, the owner would know who had passed that way!

Kniphofia caulescens (Photo by Panayoti Kelaidis)
Kniphofia caulescens (Photo by Panayoti Kelaidis)

Kniphofia caulescens stokes the heat in a late-summer garden by adding “red-hot pokers”—this plant’s delightful and very appropriate common name. When I was growing up, these were the only South African wildflowers that ever turned up in local garden centers. Back then they were invariably mislabeled Kniphofia uvaria. You can still occasionally see big clumps of those so-called “uvaria” Kniphofia in older gardens, as they’re incredibly long-lived. But the last few decades have seen far showier cultivars sold locally. Of the larger species, the most dramatic has to be the red-hot poker. In the garden, the plant’s blue foliage is almost as dramatic as a yucca’s. The flowers emerge midsummer and can last to fall—huge, erect heads of brilliant yellow and red fading to orange. Despite its yucca-like appearance, this plant does best with summer irrigation.

Salvia-pachyhphylla (Photo by Panayoti Kelaidis)
Salvia-pachyhphylla (Photo by Panayoti Kelaidis)

Salvia pachyphylla decorates our gardens with great variety. Some salvias bloom as early as April, but most wait until midsummer. I’ve grown dozens of salvias and treasure this genus. But if pressed, I’d confess the one I love the most is this native of southern California’s high altitudes. It’s really a shrub, and adds great character to the xeriscape in winter. But starting in early summer, the flowers begin to form and they continue to look spectacular in July, August and often into late fall. The flowers are blue tubes, but these are surrounded by colorful purple, pink or lavender bracts that are much showier than just the flowers alone. The one trick to growing this plant is to not give it a rich soil. It doesn’t really grow well in -vegetable-garden soil—clay or sand suits it much better. And don’t overwater it; it looks stunning with ordinary rainfall. This plant is a genuine xeriscaping gem!

Sedum tatarinowii (Photo by Panayoti Kelaidis)
Sedum tatarinowii (Photo by Panayoti Kelaidis)

Sedum tatarinowii is a white-flowered plant (it also has a bright-pink variant) collected by Harlan Hamernik of Nebraska’s Bluebird Nursery. It makes a symmetrical mound of glaucous blue foliage all summer, which is obscured by brilliant flowers in August and September. A gem well worth seeking out! It’s usually under a foot tall, so it’s better suited to smaller gardens than the often-massive forms of Sedum spectabile.

Solidago rigida (Photo by Panayoti Kelaidis)
Solidago rigida (Photo by Panayoti Kelaidis)

Solidago rigida is a goldenrod and that makes some gardeners shy away from it, because a few goldenrods spread like wildfire in rich soil. But this wonderful native is restrained and elegant. It’s rather uncommon along the Front Range, and tends to be somewhat dwarf in nature in Colorado. But in a xeriscape or garden setting with a little care, it forms a wonderfully statuesque, 4-foot-tall statement in August and September. The burnished golden-yellow flowers form dense clusters, and make a wonderful contribution to late-summer displays.


Panayoti-KelaidisPanayoti Kelaidis is senior curator and director of outreach at Denver Botanic Gardens.