Design

The Best Garden Phlox

These beauties bloom for months, stay mildew-free, and return reliably year after year

Fine Gardening – Issue 158

Garden phlox (Phlox paniculata and cvs., USDA Hardiness Zones 4–8) is one of those “memory” plants for me—a plant I remember from a long way back, before I even knew its botanical name. Perhaps that’s because it’s common in wild places throughout the eastern half of the country and beyond. Garden phlox are old-fashioned flowers that conjure up images of romantic cottage gardens and hazy summer landscapes. I hope I don’t sound like a snob when I say that, although I can appreciate the purity of the wild species, I find its muddy pink flowers a bit unsophisticated for modern gardens. Louise Beebe Wilder, in her 1916 book My Garden, has perhaps the best take on phlox: “This plant is a native, and with true American perspicacity and enterprise has forged his way from magenta obscurity to the most prominent place in the floral world.” The earliest cultivars of this native beauty were developed in Europe in the 1880s, finding their way home over time. And with even more exciting cultivars introduced in recent years, this is not your grandma’s phlox anymore.

The sweetly scented flowers, clustered in broad, rounded trusses, come in a veritable rainbow of colors. Seeing our trial in full bloom was like watching a wondrous kaleidoscopic spectacle of fancy hats in an Easter parade. Garden phlox begins blooming in midsummer, drawing in butterflies, bees, and hummingbirds aplenty for many weeks. For all that excitement, however, there is a price to be paid because garden phlox is notorious for getting powdery mildew and mites. To my surprise, though, there were a handful of cultivars that put on a spectacular show without much of a fuss.

Top performers you should get to know

These varieties were chosen as the best, not only because of their gorgeous blooms but also for their overall hardiness and proclivity to remain pest- and disease-free.

‘Shortwood’ was a sleeping giant in the first year or two—its rosy pink flowers, somewhat of a throwback to the wild species, got lost among the many vibrant colors in the trial. But at more than 4 feet tall, ‘Shortwood’ is no shrinking violet. In the end, it took top honors for exceptional performance and superior resistance to powdery mildew. Growing cheek by jowl with dozens of susceptible cultivars, it was astonishing that we never found a spot of mildew on its leaves. ‘Shortwood’ was discovered in a planting of ‘David’, another long-standing mildew-resistant phlox. I think that makes ‘Shortwood’ the gold standard for measuring mildew resistance.

‘Shortwood’

While most of the top-performing cultivars are newish, ‘Katherine’ was introduced in the 1920s but had been all but forgotten by gardeners when we put it in our trial nearly 70 years later. And am I glad we did. It was the best phlox for mildew resistance in our 1993­–96 trial and gave another strong performance in our 2001 trial. ‘Katherine’ features pretty lavender blossoms with a white eye, a combination that gives it a calming quality in a sea of rowdier colors. In our earlier trial, ‘Katherine’ topped out at 27 to 30 inches tall, whereas it was a foot taller more recently. That’s a bit of a jump, but I enjoyed the lovely flowers whether down low or up high. Due to its success in our trial, I’m hoping a new generation of gardeners will get to appreciate this oldie but goodie.

I like a flower that I can look in the eye, so it had better be tall because I’m more than 6 feet tall. ‘Delta Snow’ fits the bill; in fact, it was the third tallest phlox in our trial. Clear white flowers, dotted with a purple eye, are amply held in large clusters from early summer to fall. ‘Delta Snow’, a longtime pass-along plant from the Mississippi Delta area, was touted as mildew resistant from the start and proved to be just that for us. I love the elegance of pure white–flowered phlox, but even with a purple eye, ‘Delta Snow’ feels clean and refined.

‘Delta Snow’

The pink-and-white flowers of ‘Peppermint Twist are simply fun—the alternating stripes remind me of Starlight Mints or a child’s pinwheel. Keep this one near at hand so that the extraordinary flowers can be enjoyed up close. ‘Peppermint Twist’ was a standout in a sea of pink phlox when it was discovered in the Netherlands, and as you might imagine, its unique color form combines wonderfully with solid pink flowers. ‘Peppermint Twist’ was introduced as a compact phlox reaching only 12 to 16 inches tall and 12 to 14 inches wide, but our plants got to be twice that size in four years.

‘Peppermint Twist’

“Fiery,” “flaming,” and “screaming” are all great words to describe ‘Orange Perfection’. This phlox is not for the faint of heart. The intensity of the sultry orange flowers with magenta eyes was a bit shocking but delightful, nonetheless. I love orange—the darker the better—but I waver on whether to tone it down or simply let it shine like a beacon. I found that pairing ‘Orange Perfection’ with something blue or purple flowered, such as ‘Purple Haze’ giant hyssop (Agastache ‘Purple Haze’, Zones 6–9), ‘Heraud’ speedwell (Veronica ‘Heraud’, Zones 4–8), or ‘Souvenir d’André Chaudron’ Siberian catmint (Nepeta sibirica ‘Souvenir d’André Chaudron’, Zones 3–8), was perfection.

‘Orange Perfection’

When ‘John Fanick’ arrived from Dallas, where it is lauded for its heat tolerance, I immediately liked the fragrant, pretty-in-pink, two-tone flowers. The list of accolades that accompanied ‘John Fanick’ boasts its compact size, prolific bloom, mildew resistance, and ability to draw in butterflies like a magnet. Rather than the expected height of 2 to 3 feet tall, our plants were double the size, but every other claim was spot on. Regardless, the bounty of lovely flowers from midsummer onward makes it worth finding a spot for this charming Texan.

‘John Fanick’

One top-performing phlox is not like the others: Meadow phlox (P. maculata) looks shockingly similar to (and is often sold as) garden phlox, but its flowers are borne in cylindrical clusters and it blooms a bit earlier in summer. ‘Flower Power’ meadow phlox (P. maculata ‘Flower Power’) was one of my favorites because of the crazy amount of sweetly scented flowers, its handsome dark purple stems, and its robust bushy habit. Every summer, it lived up to its name, by blanketing its stems in tall clusters of white flowers delicately blushed with soft pink. ‘Flower Power’ is a giant for the back of a border. Unlike garden phlox, meadow phlox is untroubled by mildew, which is cause for celebration. But rabbits are beyond pernicious pests with this species—browsing was so bad that I rummaged among the stems to make sure the bunnies weren’t living in there.

‘Flower Power’ meadow phlox

In the world of garden phlox, pink is king—from light to dark, pure to muddy, solid to striped. So how does one stand apart? ‘Rowie’ had the prettiest pink flowers of all, if I’m being honest. There is an exquisiteness, almost translucency, to its flowers—clear light pink with a rosy pink eye—made all the more delightful when glistening with dewdrops. While its flowers are fairly large (1½ inches wide), they always seemed bigger atop the compact plants. ‘Rowie’ would complement anything blue, white, or soft yellow, and while it was lovely even in blazing sunlight, I bet it would be fantastic in gentler light.

‘Rowie’

Watch out for the many foes of phlox

Garden phlox are generally best grown in moist, well-drained soils in full sun to light shade. Despite being hardy and adaptable to a wide range of geographic regions, garden phlox perform best where summer nights are cool. These plants, unfortunately, are known for their susceptibility to a number of pests and diseases, especially when subjected to hot, dry, exposed soils. Here’s what you need to know about identifying and preventing some common phlox pitfalls:

Powdery mildew and garden phlox tend to go hand in hand

High humidity and warm temperatures bring on this pesky fungal disease, which commonly affects the leaves, stems, and inflorescences. The white powdery spots might remain discrete or coalesce into large patches covering entire leaves (photo, above). Severely infected leaves might wilt and prematurely fall off the plant. Although powdery mildew does not kill plants outright, it can weaken them by feeding on the nutrients in the leaves. Repeated infections can significantly decrease plant vigor over time.

Selecting resistant cultivars is the first line of defense

Your best bet for thwarting powdery mildew is to plant cultivars that avoid the disease altogether. A number of cultural practices, however, may eliminate or reduce mildew in susceptible varieties. Try (1) thinning out stems to increase air circulation through the plant; (2) planting in full sun; (3) eliminating or reducing overhead irrigation; and (4) reducing the overwintering spores by removing infected leaves and stems each autumn. Fungicides or horticultural oils and soaps can also be helpful in controlling the fungus. A mixture of one tablespoon of baking soda and one teaspoon of lightweight horticultural oil or insecticidal soap in a gallon of water applied weekly helps control the mildew, as well.

Mites might also be an issue

Two-spotted spider mites are another trouble­some pest of garden phlox. They infest the underside of leaves, especially during hot, dry periods, causing stippling and puckering as they suck out nutrients. Beyond the cosmetic aspect of the disfigured leaves, spider mites reduce the overall health of the plant. Insecticidal soaps and horticultural oils can help control infestations.

If you live in deer or rabbit country, you might be in trouble

Rabbits and deer love phlox and can quickly devastate a plant (photo, left). Repellent sprays are only somewhat effective in keeping the pernicious nibblers at bay.

 

Rabbit damage

 

Tip: Don’t forget to deadhead

To promote continued bloom and prevent self-seeding, you should be vigilant in snipping off spent phlox blooms.

 


Keep an eye out for these up-and-comers

The following phlox might not be well known to gardeners—and they are fairly new to our trial—but their performance, so far, has made us sit up and take notice.

‘Shockwave’ (P. paniculata ‘Shockwave’) isn’t just variegated; it’s über-variegated. The deep green leaves are edged and splashed in bright yellow in spring, which softens to creamy yellow as summer progresses. The leaf color is so striking that it would be fine if it never flowered. In a way, the lavender-pink flowers seem oddly paired with such an intense leaf color. I can only imagine how shocking (and pleasing) the contrast would be with cherry red, deep purple, or vivid magenta blossoms. Don’t get me wrong—the flowers are pretty and bloom well into autumn on a compact plant, only 22 inches tall and 14 inches wide. ‘Shockwave’ is known to have stable variegation, which, so far, appears to be true compared with other variegated phlox cultivars we’ve trialed.

‘Shockwave’

Plant breeders do an awesome job of creating new plants, but sometimes great plants are brought to us by nature. ‘Thai Pink Jade (P. paniculata ‘Thai Pink Jade’) was selected from a Chesapeake Bay garden, where phlox were open-pollinated and left to seed about. The result is an amazing phlox with beautiful soft pink flowers that have darker pink eyes, and it has high mildew resistance. We’ve only had ‘Thai Pink Jade’ in our garden for two years, but we like what we’ve seen, so far. The plants have been mildew-free and loaded with flowers from midsummer into early autumn. At 36 inches tall and 20 inches wide, the plants are slightly larger than expected but still compact. ‘Thai Pink Jade’ is the first in a new line of mildew-resistant selections that will be introduced in the coming years.

‘Thai Pink Jade’

‘Red Caribbean’ (P. paniculata ‘Red Caribbean’) is part of the Top Shelf series, which includes a few other cultivars like ‘Cosmopolitan’, ‘Purple Kiss’, and ‘Watermelon Punch’. (I never connected the dots that all of these cultivars were named after well-known cocktails—not that it matters much when evaluating performance.) The pink-striated petals with bright red eyes will grab your attention from midsummer onward. These vibrant flowers are borne profusely on dark purple stems, 19 inches tall and 14 inches wide. More important, the plants have been mildew-free for the past three summers—now, that’s something to toast!

‘Red Caribbean’

Four exciting cultivars in the Candy Store series were brand new to the trial in 2013. The series offers fragrant, brightly colored flowers; compact, bushy habits; and excellent mildew resistance. Bubblegum Pink (P. ‘DITOFRA’) aptly describes its bright pink flowers. The coral pink flowers of Coral Crème Drop (P. ‘DITOMDRE’, pictured) are brilliant on their own, but I particularly like the way they pop against the nearly black-purple upper leaves. Cotton Candy (P. ‘DITOMFAV’) has flowers of soft pink with a splash of white circling a darker eye. The bright purple flowers of Grape Lollipop (P. ‘DITOMSUR’) are notable for the prominent white splash at the base of each petal. All of the cultivars were about 12 inches tall and 10 inches wide the first year. Rabbits, unfortunately, loved this group as much as—or maybe more than—I do; they were constant nibblers throughout the summer, which didn’t allow the plants to bush up until late in the season. In spite of the rabbits’ voracious appetite, the plants bloomed pretty well from early summer to midfall. I look forward to watching these wonderful new phlox next year, if I can just get the rabbits to move along.

Candy Store™ Coral Crème Drop

Trial Parameters

Since 1993, the Chicago Botanic Garden has evaluated 110 different phlox in our comparative trials.

How long: A minimum of four years

Participants: Aside from garden phlox, the trial included a number of cultivars of Phlox × arendsii and P. maculata, which boast greater mildew resistance and are often sold as P. paniculata.

Zone: 5b

Conditions: Full sun; well-drained, alkaline, clay-loam soil

Care: We pro­vided minimal care, allowing the plants to thrive or fail under natural conditions. Besides observing their ornamental traits, we monitored the plants to see how well they grew and adapted to environmental and soil conditions while keeping a close eye on any disease or pest problems and assessing plant injury or losses over winter.

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This article was originally titled Garden Phlox that Don’t Disappoint
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