This fast-filling pollinator plant adds a zap of color to the summer garden
Monarda, a flowering perennial otherwise known as bee balm or wild bergamot, is the subject of the latest research report by Mt. Cuba Center’s research team. The study observed 40 selections of plants from the Monarda family over a period of three years. The report details the top-performing monarda selections for the region, as well as information about the plants’ pollinators, history and care.
“Monarda is an easy beginner plant,” said George Coombs, Mt. Cuba Center’s Manager of Horticultural Research. “They’re worth a try, especially if you’ve got a normal-to-moist spot in your garden. It spreads easily and is a great plant for covering large areas that you don’t have the time or energy to take care of.”
Blooming in the heat of high summer, monarda fills gardens with electric hues of pink, purple and red and grows well with little help from gardeners. As a member of the mint family—known for plants with scented foliage which spread readily—monarda will creep outwards after it’s planted. In fact, a gardener’s main task with this plant is to rein it in every once in a while. While not as fast-growing as spearmint, monarda will grow about a foot in each direction every year.
In the wild, monarda can be found in meadows where it’s used to bright sun conditions and tough competition from other plants. When planted in a nutrient-rich, evenly moist garden bed, it takes off.
“They’re really great plants if you have a space you need to fill and need to fill it quickly,” Coombs said. “If you have a nice rich soil, they spread further than if they were in a leaner soil.” There’s a bright side to that growth: As the plant grows outward, its center will die out after a few years. Simply divide the plant and replace the dying center mass with the rejuvenated new growth.
Monarda plants are commonly available in the perennials section of most garden centers, including Old Country Gardens in northern Wilmington.
“Most customers look for monardas with red flowers because they feel that’s going to be the most attractive to hummingbirds,” said Kathy Palmer, a manager at Old Country Gardens. “We try to have a variety.” If customers want a specific cultivar that is not available in the nursery, they can place a request with Palmer’s staff.
For success with monarda in the home garden, Palmer emphasized placing the plant in an area with good air circulation—not against a building—in order to prevent powdery mildew, a garden disease that plagues monarda plants.
Powdery mildew – a common frustration
In a garden setting, monarda’s vigorous growth makes it prone to a fungal disease called powdery mildew, a common ailment of monarda and many other garden plants that casts gray fuzz over leaves and stems. This appears in the summer because warm, humid nights help spores germinate, and hot, dry days help it spread. The disease isn’t fatal to the plant, but it can make the garden look distressed.
“We tried to get our hands on as many cultivars as possible, including ones that people would be likely to come across at a garden center, to see if there are any that have improved mildew resistance,” Coombs said.
The research showed several selections which were completely resistant to the disease and many plants with lower resistance to powdery mildew, but which had flower displays that put them ahead of the pack. Gardeners must choose which trait they value most.
“If you have a garden that you want to look clean—maybe it’s closer to your sidewalk—go for a mildew-free cultivar,” Coombs said. “Or if it’s at the back of your property and you just want to see a ton of color, drop the importance of the mildew resistance. There’s one, ‘Purple Mildew Resistant’, which was really clean all season long, didn’t get a drop of mildew on it, but put out just a handful of flowers. In my mind that’s great, but not if I’m growing this plant for its flowers.”
Once monarda gets powdery mildew, Coombs recommends hosing off the plants or cutting them back.
“There’s not a lot you can do,” Coombs said. “It usually goes away after a long rain.”
When it comes to native plants, flowers mean supporting pollinators. In 2016, Mt. Cuba Center enlisted a team of citizen scientists to observe pollinator activity in the Trial Garden.
“Our citizen scientists took shifts throughout the summertime and tracked on which plants they saw butterflies and hummingbirds activity,” Coombs said. “The selections we found the most butterflies on were the ones that put out the most flowers and bloomed for the longest period of time. Some of the plants that were top performers in the study because of their great floral displays were also really good at attracting butterflies.”
The clear winner for hummingbirds is Monarda didyma ‘Jacob Cline’. Citizen scientists observed 273 hummingbird visits to this plant. The next-most popular plant, Monarda ‘Gardenview Scarlet’, had 39 visits by hummingbirds. These popular hummingbird-attracting selections were all red-flowered, but the runaway success of ‘Jacob Cline’ might have more to do with its height and the size of its flowers.
“It means the hummingbird can actually get into the flower,” Coombs said. “The butterflies were seen most often on the smaller and average-sized flowers.”
Butterflies and moths favored plants which produced the largest number of 2-3” wide flowers, like Monarda fistulosa ‘Claire Grace’, which blooms in early July and produces a reddish purple flower.
A plant trial is a study in which plants from the same family are planted together and observed by researchers who collect data. In Mt. Cuba Center’s Trial Garden, researchers evaluate native plants and their cultivars to provide the horticulture industry with information about the best-performing plants in the mid-Atlantic region.
“We’re not babying plants in our trials,” Coombs said. “We’re stressing them. We do that so we can see differences between different cultivars and amplify those differences.” The plants receive additional water during their first year in the ground, but after that they depend on rain.”
The top-rated monarda selections in the study struck a balance between powdery mildew resistance and floral display. The top ten cultivars were: Monarda fistulosa ‘Claire Grace’, M. ‘Dark Ponticum’, M. ‘Violet Queen’, M. ‘AChall’ (Grand Marshall™), M. ‘Judith’s Fancy Fuchsia’, M. ‘Colrain Red’, M. ‘Raspberry Wine’, M. ‘Purple Rooster’, M. ‘On Parade’, and M. ‘Gardenview Scarlet’.
Read the results of the trial in Monarda for the Mid-Atlantic Region, or explore the trial on our Trial Garden page. This article originally appeared in the News Journal on February 23, 2017.