Annuals for Connoisseurs Plant guru Mark Dwyer shares favorites

Annuals for Connoisseurs

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Plant Guru Mark Dwyer shares some of his favorite annuals at iLandscape

by Nina A. Koziol

Far too often, annuals are

thought of as expensive accessories to temporarily plug gaps before more important plants fill in the space. Or they’re a luxury — the “wow” element — dazzling during the growing season. Mark Dwyer showed several tantalizing reasons to use annuals in your clients’ gardens during his virtual presentation at this year’s iLandscape conference.

“Seasonal plantings offer outstanding color from both flowers and foliage,” said Dwyer, owner of Landscape Prescriptions by MD. “Using annuals in borders, compositions, and containers creates months of interest and may provide scent, pollinator value, and food.” He also uses herbs, kale, and other edibles as decorative and useful annuals in his designs. Dwyer was director of horticulture at Rotary Botanical Gardens in Janesville, Wisconsin, for over 20 years. He knows his stuff.

“We planted and featured about 150,000 annuals representing 600 varieties each year,” Dwyer said. So it’s no surprise he enjoys annuals — a lot! “Other benefits include extended color, brightness in sun and shade, and sometimes fragrance.” He did note that annuals are not always an easy sell to some clients. “There’s a lot of expense involved in purchasing and maintenance,” he says. “But the benefits usually outweigh the downside.” Foliage and flower

Dwyer carefully considers foliage and flowers when designing with annuals. “The composition is equally important not only for flower power, but for extended interest of foliage that becomes a foil for surrounding plants. Many annuals offer impact like Begonia Jurassic Silver Swirl with its silvery leaves. That’s its primary feature — you may never see the blooms. It’s the visual, textural component that is interesting.”

Some annuals offer fragrance at night to attract pollinators while others, like zinnias, can be used by clients as cut flowers for indoor arrangements. There’s also an incredible assortment of new varieties of old favorites suitable for containers and bedding plants.

Begonia Jurassic Silver Swirl

“The marigold was the gateway plant that my mom got me interested in as a youth,” Dwyer said. The new cultivars are not your granny’s marigolds. “Breeders have extended coloration well into frost. They’re just dynamite in the landscape in full sun, and they’re very durable and tough.” At Rotary Botanical Garden, he grew 30 to 40 varieties every year. Now, he’s particularly fond of the Marvel™ series.

“Our clients are spending more time gardening, and gardening in containers,” said Kim Hartman, member of ILCA’s education committee. “We’re getting new, exciting, and innovative ideas from Mark.”

Here are a few of the annuals that fascinate him.

Marigold MarvelTM series

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“I’m a huge fan of zinnias, like the Profusion series, which has been out for many years. They’re heat-tolerant and relatively low maintenance, and they tend to be self-cleaning, producing flowers through frost. All Profusion series zinnias are excellent. They’re only 15 inches tall and constantly produce new flowers.” He’s particularly fond of Zinnia ‘Profusion Red Yellow Bicolor.’ “The new and old blooms are dynamite, and the older blooms age to a russet pink. It’s an All-America Selections winner.”

If you’re looking for a shorter-stature zinnia, Dwyer recommends the Sahara series. “The Double Zahara Yellow improved form is great if you really want bright impact. Use it as a specimen plant in a container or dotted through the landscape. It’s a very effective warm color — yellow, orange and red really pop in the landscape.”

Petunias are another of Dwyer’s favorite workhorses. “Petunia ‘Headliner Crystal Sky’ is a great performer in hot summers, planted in a basket, container, or the edge of a border. I like the subtle look of the violet venation in the throat and speckling on the petals.” Petunia Bees Knees (Petunia ‘Balcobees’) also gets high marks. “Yellow petunias were ruddy looking 15 to 20 years ago, and they faded quickly to cream and didn’t look great, but they are improving all the time. This cultivar maintains the dark yellow throat and white edges. It looks quite nice in mass plantings.”

Breeders are constantly making improvements to the popular annual million bells (Calibrachoa). “There are mounding, semi-trailing, and trailing forms and so many exciting color ranges. The challenge is providing proper drainage and plenty of fertilizer,” Dwyer said. “They lean toward acid fertilizers. If the foliage is yellow, time to fertilize.” At Rotary Botanical Garden, million bells tended to do better in baskets and as trailers, he said. “All calibrachoas have a heavy flower count, and I love ChaCha™ Tangerine and Diva Hot Pink.” He does have one caution if million bells are planted directly in the ground: “There’s a lot of moisture splattering, and if the soils are overly cool at planting time, it can lead to root rot and fungal problems. Consider container use instead or provide elevated situations with sharp drainage and fertilizer.”

Zinnia ‘Profusion Red Yellow Bicolor’

Calibrachoa Cha-Cha™ Diva Hot Pink

Annual phlox is another unused plant. “The Giselle™ series has been around for about six years, and I’ve grown all of them. I think they’re spectacular for the flower power, and they’re slightly fragrant.” His only concern is that the plants don’t look like that all the way until frost. “They peak nicely in June through July and into August and continue to flower. But when the evening temps start to dip, they peter out.” At 10 to 12 inches tall, they lend themselves to containers, beds, or borders.

Lancelot salvia (Salvia canariensis ‘Lancelot’) — aka Canary Island sage — shines with beautiful silvery leaves and magenta flowers. “Salvias are slam dunks not just for butterflies, but also for hummingbirds.”

Annual phlox Giselle™

Salvia canariensis ‘Lancelot’

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Dwyer can’t get enough of celosias, either. “Lizzard leaf celosia (Lizzard Leaf Sol™Celosia argentea) is one that’s often promoted as a container plant. In full sun, it gets this glossy foliage and then wheatlike flowers. They’re about 15 inches tall, whereas Candela Pink celosia is 30 inches tall and very heat tolerant.” Good drainage and full sun will keep these plants performing until the fall frosts.

Sweet potato vines have been the darlings of hanging baskets and window boxes for the past 15 years or more. “The older varieties know no bounds,” Dwyer said, “and, Japanese beetles find them tasty.” In the last three years, he’s photographed about 40 trailing varieties from lime-green to yellow, variegated, brown, and near-black. That’s why he’s fascinated by new cultivars that are not only more compact, but also climb. “They have new twining and climbing sweet potato vines, and I’ve been very excited about them. Medusa Green out of the Sweet Caroline series is very fine-leaved and fine-textured.”

What’s old is new again with coleus that offer several months of interesting color and textures. Dwyer particularly likes Dragon Heart™ coleus, a new variety with very bright fuchsia and gold leaves. “Don’t ever let them bloom — and pinch them back to the second set of leaves to encourage more foliage. Don’t be shy about snipping them back.” He appreciates the nuances of the leaves, which can be large with rounded edges, small, or deeply lobed. And here’s a little surprise: “The majority can take full, blazing sun. In shade, Dragon Heart coleus is green and fuchsia. It’s not bad, but it loses that bright look. Ten years ago, they were called “sun” coleus, but the majority of coleus take full sun. Don’t ever put coleus in full shade — it will never thrive. They’re not drought tolerant, either. They like lots of moisture.” At Rotary Botanical Gardens he routinely applies fertilizer every three weeks from June to August because the plants are heavy feeders.

New begonias for sun and shade have hit the market and serve as a replacement for Impatiens. “Don’t consider begonias just a shade plant,” Dwyer said. “Double Apricot can do well in full sun with ample moisture. They have a certain durability in the shade, but ultimately they’re happy in full sun. There’s a huge array of trailing, cascading types.”

Rex-type begonias are perfect for shade. Dwyer likes a new variety, Jurassic Jr. ‘Purple Spec,’ for the leaf markings. “It rarely blooms in our climate. They can be brought in as houseplants. Start

Celosia argentea ‘Sol™’

Coleus ‘Dragon Heart’ Begonia ‘Spring Fling Buttercup’

researching rex begonias, and you’ll find some great selections. In the shady landscape they need perfect, sharp drainage, but adequate water.”

When it comes to the new diseaseresistant varieties of Impatiens, Dwyer says, “I think the entire Beacon® series is excellent, and there are six to seven cultivars. It’s mildew-resistant, and downy mildew has been a bummer. We went from planting 30,000 every spring to zero. The breeding work in the Beacon series is solid. They’ve inoculated it with the mildew, and it’s made it through. I feel standard impatiens are back — extremely shade tolerant and mildew resistant.” And who can argue with that?

Impatiens Beacon orange