These perennials can stand up to summer's heat

During the dog days of summer, a variety of flowers, such as black-eyed Susans and purple coneflowers, continue to bloom.

Adrian Higgins/ The Washington Post
A hardy ice plant at the Chanticleer Garden in Wayne, Pa., produces a colorful display of flowers well into August.

Plant forms create structure in a garden, and leaf ornament brings texture, but let's face it, flowers provide the greatest thrill. I'm thinking of this now as the month-long show of the day lilies begins to wane and gardens generally enter the floral wasteland of July and August.

The truth is, you have to work at filling this gap to keep the garden from looking washed out and tired by the heat. Annuals bridge the dog days, along with the tropicals that are so popular today, but there's a raft of perennials that provide weeks of show as the days begin to shorten and the heat sets in.

There are some obvious candidates, all of which I can see from my porch. The stand of purple coneflowers is high from the spring rains and in full color. In a month the seed heads will be black and ripe and draw a resident tribe of chattering goldfinches. Coneflower breeders have been hard at work to bring about fresh varieties, some more enduring and worthy than others.

Allan Armitage lists and describes 47 hybrids in his book "Herbaceous Perennial Plants." More are being introduced, and the color range today includes clear reds, golden yellows, wine purples and white. Pink Double Delight has dazzling pompom flowers on strong 24-inch stems. Its white counterpart is Coconut Lime, named for its green-tinted creamy blooms.

Magnus is an older selection but still a champ. The petals, or rays, don't droop as much as the wild purple coneflower, making the blooms appear bigger. I was in a garden the other day and found the Tennessee coneflower, daintier than the purple coneflower, with slender petals that are turned up a little. This species is endangered, so it's important to obtain plants that have been ethically propagated and not collected in the wild. Rocky Top is a named variety.

Wild quinine, or parthenium, is a wonderful, underused July perennial, upright and bold with clusters of white flowers that draw butterflies.

One daisy plant worth getting to know is the Mexican hat, or Ratibida, named because the central disk rises so high that the dainty bloom looks like a sombrero. Most are yellow, but a variety named pulcherrima has beautiful mahogany-red petals.

A friend raves about a recently introduced variety of blanket flower, Gaillardia Oranges and Lemons. Its flowers are a muted blend of orange and yellow and, to my eye, far more pleasing than the clunky red and yellow of traditional blanket flower varieties. It started to bloom in late spring and will keep going until frost.

Butterfly weed, Asclepias tuberosa, has already begun to show its clusters of orange blooms and is drawing monarch butterflies. I saw it paired daringly but effectively with the magenta-flowered poppy mallow or winecup (Callirhoe involucrata). The flowers are held aloft from the low-growing foliage, and it blooms for weeks in hot, sunny locations. It deserves to be used more than it is.

All these plants require a sunny site and, most of all, well-drained soil. They won't thrive in sodden heavy clay.

The leaves of the poppy mallow resemble those of the hardy geranium or cranesbill. Speaking of which, the much-admired geranium variety Rozanne produces violet-blue flowers that don't stop, or so it seems.

The hardy ice plant is a mat-forming succulent with both spring and summer blooming species that produce a carpet of daisies in vivid colors. Delosperma cooperi began blooming a violet-pink in June and will flower well into August. It insists upon excellent drainage and would be good for a poor, dry site that has been amended with gravel and given a gravel mulch.

My black-eyed Susans have begun to flower. I have the classic Goldsturm variety selected for its large and plentiful flowers, though it is prone to septoria leaf spot, especially after a wet spring. I treated mine with a copper spray about a month ago, and the foliage has remained mostly clean. I am told that a variety of Rudbeckia fulgida named deamii is much more resistant to the disease and may be worth planting instead. Black-eyed Susans are a bit of a cliché, as is the wispy blue Russian sage, but both remain stalwart flowering perennials in July and August.

If your soil is poorly drained, add lots of organic matter and then put in some summer perennials that will take moister soil. The obedient plant (Physostegia virginiana) is a particularly long-flowering summer perennial. The white variety Alba has begun to bloom. Pink forms flower a bit later and last into early fall.

The persicaria variety named Firetail, with its slender crimson flowers above sprawling foliage, loves moisture and has begun to flower. It will continue until after frost without any need for deadheading. Armitage notes that it needs space and can get floppy. I simply cut fallen stems to the ground, and new ones return.

The gooseneck loosestrife forms a three-foot-high ground cover and is smothered in white floral racemes in July and August. It will spread in wet conditions and look painfully wilted in dry soil, so place it in a moist area where it can be contained.

All these plants need a lot of sunlight. What about shadier gardens? Shade gardens are more about leaf textures and associations than flowers, but many hosta varieties are effective summer bloomers. Varieties of Hosta plantaginea often have a bonus of being fragrant. Two classic varieties are Royal Standard and Honeybells.

In July, a shade perennial named yellow wax bells, or kirengeshoma, develops its budding flower stalks above broad lobed leaves. In August the plant is full of large, bell-like, lemon-yellow flowers.

A far less familiar shade perennial is the palmate umbrella plant, which has lovely cutleaf foliage and a flower stalk rising two feet or more bearing clusters of pinkish or white fuzzy flowers. Its botanic name, if you want to track it down, is Syneilesis palmata. It is one of those novel plants that remind you that the garden offers endless possibilities, no matter the season.

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