AMES, Iowa – Bees, butterflies and hummingbirds are attracted to the red, white, pink, lilac and purple bee balm tubular flowers. Deadheading these late spring or early summer bloomers will encourage repeat blooms. Horticulture specialists with Iowa State University Extension and Outreach answer bee balm questions this week. To have additional gardening questions answered, contact the specialists by calling or emailing the ISU Extension and Outreach horticulture hotline at 515-294-3108 or firstname.lastname@example.org.
Bee balms (Monarda species) perform best in full sun. The planting site should receive at least six hours of direct sun per day. Plants grown in partial shade won’t flower as heavily and are more susceptible to powdery mildew. Bee balms also prefer moist, well-drained soils.
Bee balms like an even supply of moisture during the growing season. For best performance, water bee balms every seven to 10 days during dry periods. When watering, soak the soil to a depth of 6 to 8 inches. Apply a mulch around plants to conserve soil moisture and reduce the frequency of watering.
Bee balms don’t require frequent or heavy fertilizer applications. Sprinkling a small amount of an all-purpose garden fertilizer, such as 10-10-10, around each plant in early spring is usually sufficient. Avoid excessive fertilization. Frequent or heavy applications of fertilizer encourage rampant, succulent growth and may increase the severity of powdery mildew.
Bee balms spread rapidly via underground stems or rhizomes. In addition, the center of the plant often dies out within a few years. To control their spread and rejuvenate plants, it’s advisable to dig and divide bee balms every two to three years. Early spring is the best time to dig and divide bee balms. Dig up the plants as soon as new growth appears in spring. Divide the clump into sections with a sharp knife. Each section should have several shoots and a good root system. Immediately replant the divisions.
The symptoms on your bee balms (Monarda spp.) are most likely due to powdery mildew. Powdery mildew is a common fungal disease on bee balms. Symptoms are most severe on over-crowded plants and those growing in partial shade.
Cultural practices can reduce the severity of powdery mildew. When planting bee balms, select a site that receives at least six hours of direct sun each day and space plants 2 to 2½ feet apart. Move plants growing in partial shade to a sunny location. Divide bee balms every two to three years to prevent overcrowding. Remove and destroy disease-infested plant debris in fall. If cultural practices fail, fungicides can also be used to control powdery mildew.
The best way for home gardeners to avoid the annoying problem of powdery mildew is to select and plant mildew resistant varieties. Varieties that possess good to excellent resistance to powdery mildew include ‘Marshall’s Delight’ (bright pink flowers), ‘Jacob Cline’ (deep red flowers), Grand Marshall™ (fuschia-purple flowers) and ‘Raspberry Wine’ (wine red flowers).