Phlox paniculata Flame Series

From GPN - Greenhouse Product News

Published Volume 16 Number 3 · Link to Article

Thanks to improved breeding and plant selection, garden phlox is regaining popularity.

By Paul Pilon

Phlox paniculata is most recognized by its long-lasting display of fragrant, intensely colored flower clusters during mid-summer. This old fashioned perennial also is commonly known as garden phlox or tall phlox. Because of improved breeding and plant selection, garden phlox is regaining popularity as improved cultivars come into the market.

One of the better new introductions is the Flame series, a result of the breeding efforts of Bartel's Breeding in The Netherlands. It offers growers a compact alternative, reaching 15-18 inches in height, to the historically taller (30-48 inches) garden phlox cultivars. There are four colors in the Flame series: Light Pink, Lilac, Pink and Purple.

Phlox paniculata performs well across a wide portion of the United States, throughout USDA Hardiness Zones 3-8 and AHS Heat Zones 8-1. It prefers full sun, although in the South it performs best when partial shade is provided. This native American perennial is commonly used as an aromatic border plant to attract hummingbirds and butterflies to the garden, for accent plantings and as a cut flower. With its shorter plant habit, the Flame series can be used in container plantings, expanding the marketing opportunities for this popular perennial.


The Flame series is vegetatively propagated using unrooted tip cuttings. Since a plant patent is being sought (PPAF-Plant Patent Applied For), unlicensed propagation of this cultivar is prohibited.

Cuttings can be successfully rooted by sticking them directly into a pre-moistened, well-drained growing medium in plug trays with large cell sizes or directly into the final container. Dipping unrooted cuttings into a solution of indolebutyric acid (IBA) at rates between 750 and 1,000 ppm is not essential for successful rooting but does tend to provide a slightly higher rooting percentage and reduces rooting time.

Place the cuttings under low misting regimes for about the first 10 days of propagation. When possible, it is usually best to propagate under high humidity levels (90-percent relative humidity) with minimum misting. The misting and humidity levels can be reduced gradually as the cuttings form calluses and root primordia. Begin feeding with 150 ppm nitrogen at each irrigation using complete water soluble fertilizers as the cuttings are forming roots (usually between 10 and 14 days). With soil temperatures being maintained at 68-74º F, plants usually will be well rooted in 3-4 weeks.


Phlox performs best when grown in a moist, well-drained medium with a slightly acidic pH of 6.0-6.5. When planting into 1-gal. or larger containers, I recommend growers use two 72-cell liners per container. Using multiple liners creates fuller-appearing containers with more shoots and blooms per pot. Many growers plant liners during the late summer of the year prior to the intended date of sale. Planting liners of phlox in this manner will allow them to bulk up, produce more flowers per plant and bloom earlier than when they are planted and grown only in the spring.

Garden phlox are moderate feeders and perform best when Á either a constant liquid fertilization program is used feeding at rates of 75-150 ppm or using higher rates of 150-200 ppm as needed. Fertility also can be delivered using controlled release fertilizers by topdressing the media surface using the medium rate listed on the product's label or incorporating fertilizers into the growing medium prior to planting at a rate equivalent to 1-11?4 lbs. of nitrogen per cubic yard of growing medium. The Flame series performs best under average watering regimes. When irrigation is needed, water thoroughly and allow the medium to dry between waterings.

Growers commonly observe aphids, spider mites, thrips and whiteflies feeding on garden phlox. Other insects commonly observed on phlox include: caterpillar, grasshopper, leafhopper, slug and spittlebug. In most cases, these insects can be detected with routine crop monitoring and do not require proactive strategies.

Of the plant pathogens phlox are the most susceptible to, powdery mildew is observed the most frequently. The Flame series appears to be highly resistant to powdery mildew infections; however, under severe conditions this disease may still develop. Alternaria, Botrytis, Cercospora leaf spot, Fusarium, Pythium, Phytopthora, Rhizoctonia and stem canker have also been observed attacking garden phlox.

To control foliar diseases, it is best to manage the environment by providing the proper plant spacing and adequate air movement, reducing free moisture on the leaves and controlling the humidity. The onset of root rot diseases often can be prevented by avoiding overly moist conditions. If growers have historically faced these diseases on other phlox cultivars, it may be highly beneficial to follow preventative programs using the appropriate chemicals.

With its compact growth habit, controlling plant height is usually not necessary when producing the Flame series. Many growers produce plants at pot-tight configurations and still do not need to control stem elongation.


To improve marketability, the phlox Flame series can be forced to bloom throughout the year. Forcing garden phlox into flower out of season involves following a few key guidelines.

To produce full pots of high quality, the Flame series should be bulked up prior to forcing. After the liners are planted into the final container, they should be grown at 12- to 13-hour photoperiods with temperatures of 64-70º F to keep them actively growing. The length of the bulking period depends on the size of the pot; 1-qt. pots may require three weeks of bulking, while 1-gal. containers might require four weeks and so on. To promote branching, it is recommended to pinch plants 4-6 weeks after planting, leaving 8-10 nodes just prior to or at the time of planting.

The Flame series does not require vernalization for flowering but shows 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. Flame can be vernalized in the final container or as a liner prior to transplanting. I recommend growers provide at least six weeks of cold temperatures at 35-44º F.

Phlox paniculata are long-day plants, requiring at least 14 hours of light each day for flowering. Shorter photoperiods will cause them to flower poorly or not at all. When the natural day lengths are short, it is recommended to provide 14-hour photoperiods or night-interruption lighting. The highest quality plants are produced in high light environments (minimum 3,000 foot-candles). Under low light intensities, the size and quantity of flowers per plant are often reduced, and the stems are often weak and cannot support the weight of the flower heads. During periods when the light levels are naturally low, 300-400 foot-candles of supplemental lighting should be provided.

The time it takes Flame to bloom after vernalization and the proper photoperiod have been provided is a function of temperature. The Flame series grown at 68° F will take 10-12 weeks to reach flowering, while plants grown at 62° F will flower in approximately 14 weeks. Plants that have received a cold treatment typically flower 1-2 weeks earlier than non-cooled plants. The time to bloom also varies with climate, season, location and environmental conditions.


Phlox paniculata Flame is available to the industry as unrooted cuttings exclusively from Ball Seed ( Rooted liners are available from many Ball Seed rooting stations and perennial propagators including C. Raker and Sons, Inc.; Center Greenhouse, Inc.; Dickman Farms; Gro N Sell, Inc.; Gulley Greenhouse; and Skagit Gardens, Inc.

Source: Greenhouse Product News   March 2006   Volume: 16 Number: 3
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