July 2008 Culture

Monarda Didyma ‘Pink Lace’ By Paul Pilon

When in bloom, monarda delivers an eye-catching, spectacular display of color to summer gardens. Monarda 'Pink Lace' is no exception, producing an abundance of lipstick-pink flowers with purple centers atop dark stems from midsummer to early fall. Additionally, 'Pink Lace' offers a compact alternative — at 16 inches — to the historically taller cultivars, which typically reach 30-36 inches in height. Future Plants brought this exciting cultivar to the marketplace.

This old-fashioned garden perennial, commonly known as bee balm, performs well across a wide portion of the United States, throughout USDA Hardiness Zones 4 to 9. Bee balm is native to eastern North America, where it can be found growing along riverbanks. Monarda prefers sites with moist soils and full sun but will grow well when some light shade is provided.

This Native American perennial is commonly used as border plants, accent plants, in mass plantings and as cut flowers. The flowers attract hummingbirds, butterflies and honeybees into the garden, but they're deer resistant. The compact habit of 'Pink Lace' makes it ideal in container plantings, further expanding its marketing opportunities.

Propagation

Monarda 'Pink Lace' is vegetatively propagated using unrooted tip cuttings. Because a plant patent is being sought (PPAF), unlicensed propagation of this cultivar is prohibited.

Licensed propagators root tip cuttings by sticking them directly into a premoistened, well-drained growing medium in liner trays with large cells or directly into the final container. Dipping unrooted cuttings into a solution of indole- butyric acid (IBA) at rates of 500-750 ppm is not essential for successful rooting but does tend to provide a slightly higher rooting percentage and a shorter rooting time.

Place the cuttings under low misting regimes for about the first 10 days of propagation. When possible, propagate at high humidity levels — 90 percent relative humidity — with minimum misting. The misting and humidity levels can gradually be reduced as the cuttings form calluses and root primordia. Begin feeding with 100-ppm nitrogen at each irrigation, using complete water- soluble fertilizers as the cuttings are forming roots (usually between 10 to 14 days). With soil temperatures being maintained at 68-74¡ F, cuttings will usually be well rooted in three to four weeks.

Production

Monarda 'Pink Lace' performs best when grown in a moist, well-drained medium with a slightly acidic pH of 5.8-6.5. Many growers plant rooted liners during the late summer of the year prior to the intended date of sale. Planting liners of monarda in this manner will allow them to bulk up, produce more flowers per plant and bloom earlier than when planted and grown only in the spring.

Bee balm are moderate feeders and perform best under either a constant liquid fertilization program at 75-150 ppm or higher rates of 150-200 ppm as needed. Fertility can also be delivered using controlled-release fertilizers by topdressing the media surface using the medium rate listed on the product's label, or incorporating them into the growing medium prior to planting at a rate equivalent to 1-1_ pounds of nitrogen per cubic yard of growing medium. 'Pink Lace' performs best under "average" watering regimes. When irrigation is needed, water thoroughly and allow the medium to dry between waterings.

Controlling the plant height is not usually necessary when producing the already-compact monarda 'Pink Lace'. Growers can produce them at pot-tight configurations and do not often need to control stem elongation. If height control is necessary, spray applications using a tank mixture of daminozide (B-Nine, Dazide) at 2,000 ppm and uniconazole (Concise, Sumagic) at 3 ppm will provide adequate control.

Insects and Diseases

Growers commonly observe aphids, spider mites, thrips and whiteflies feeding on monarda. Caterpillars, grasshoppers, leafhoppers, leafminers and slugs may also be observed on bee balm. Aphids and spider mites are usually the most prevalent insect pests. In most cases, insects can be detected with routine crop monitoring and do not require proactive strategies.

Cercospora leaf spot, powdery mildew, Rhizoctonia crown rot, rust and Southern blight (Sclerotium) are the plant pathogens that commonly attack bee balm. Of these plant pathogens, powdery mildew is observed most frequently. Many growers implement preventative fungicide applications rotating various products (azoxystrobin, myclobutanil, potassium bicarbonate, triadimefon and triflumizole) effective at controlling powdery mildew diseases.

Forcing

To improve marketability, 'Pink Lace' can be forced to bloom throughout the year. Forcing monarda into flower out of season involves following a few key guidelines.

To produce full, high-quality pots, 'Pink Lace' should be bulked up prior to forcing; growers commonly plant liners in the late summer the year before they are to be sold. Spring-planted liners often result in smaller finished plants and may not properly fill out the container (particularly large container sizes). Growers should produce 'Pink Lace' only in 1-gallon or smaller pots when planting liners in the spring.

'Pink Lace' does not require vernalization for flowering but is cold beneficial, exhibiting great benefits following a cold treatment: Vernalized plants grow more vigorously and tend to flower more rapidly and uniformly than plants with no exposure to cold. They can be vernalized in the final container or as plug liners prior to transplanting. Provide at least nine weeks of temperatures below 44¡ F.

Monarda is an obligate long-day plant, requiring at least 14 hours of light each day for flowering. When the natural daylengths are short (less then 14 hours), it is recommended to provide 14-hour photoperiods or night-interruption lighting. The highest-quality plants are produced in high-light environments of at least 3,000 foot-candles.

The time to bloom after vernalization and the proper photoperiod provided is a function of temperature. 'Pink Lace' grown at 68¡ F will take nine weeks to reach flowering, while plants grown at 62¡ F will flower in approximately 13 weeks. Plants that have received a cold treatment typically flower one to two weeks earlier than noncooled plants. The time to bloom also varies with climate, season, location, environmental conditions and size of starting materials used.

Availability

Rooted liners of monarda 'Pink Lace' can be acquired from many reputable perennial propagators including Pioneer Gardens, Inc. (www.pioneergardens.com) and Skagit Gardens, Inc. (www.skagitgardens.com).