June 2006

Coreopsis grandiflora ‘Sunfire’ By Paul Pilon

With its ease of production and ability to flower the first year, Coreopsis grandiflora 'Sunfire' is a great addition to spring perennial programs. 'Sunfire' produces an abundant supply of large, single, yellow blooms with burgundy-red centers, and flowers are held over a compact, attractive mound of foliage. Flowering occurs earlier than most other C. grandiflora cultivars; 'Sunfire' even blooms 7-10 days earlier than the early-blooming cultivar 'Early Sunrise'. With its early and uniform flowering, 'Sunfire' has earned the Fleuroselect Quality Mark, which is widely recognized by gardeners and professional growers throughout the world.

In the landscape, 'Sunfire' grows best under full sun and will spread 12-18 inches while maintaining a height of 18-24 inches. In Southern locations they perform best when some partial shade is provided. 'Sunfire' is hardy in USDA Hardiness Zones 4-9 and AHS Heat Zones 12-1. Plants are generally considered short-lived, especially in hot, humid climates. This American native, commonly known as tickseed, is used as an accent plant, border plant, cut flower and in mass plantings and patio containers.

Propagation

Coreopsis 'Sunfire' is propagated from seed. Cover seeds lightly with germination mix or medium-grade vermiculite to help keep the seed moist during germination. The seed flats should be moistened and moved to a warm environment where temperatures can be maintained at 68-72¼ F for germination.

Light is required for germination and should be provided. Many growers use germination chambers during this stage to provide uniform moisture levels and temperatures. Using germination chambers is optional, as 'Sunfire' will successfully germinate in the greenhouse.

The seeds should germinate in 4-8 days. Following germination, reduce moisture levels somewhat, allowing the growing medium to dry out slightly before watering to help promote rooting. As the plug develops, light levels can be increased gradually from 500 foot-candles following germination to 2,500-5,000 foot-candles at the final stage. Fertilizers are usually applied once the cotyledons are fully expanded. Apply 100- to 150-ppm nitrogen every third irrigation or 75 ppm with every irrigation using a balanced water-soluble source. When plugs are grown at 65¼ F, they are usually ready for transplanting in 5-7 weeks.

Production Basics

'Sunfire' is well suited for container production in 1-qt. to 1-gal. sizes. Plants perform best when grown in a moist, well-drained medium with the pH maintained between 5.8 and 6.4. Many commercially available peat- or bark-based grow-ing mixes work well provided there is good water-holding ability and adequate drainage.

Coreopsis prefers a moist, not wet, growing medium. Water as needed when plants are young and becoming established. Once the plants are large, they will require more frequent irrigation, as they will dry out rather quickly. When irrigation is needed, I recommend growers water plants thoroughly, ensuring the entire growing medium is wet or nearly saturated.

Tickseed is a moderate feeder; growers should deliver nutrients using water-soluble or controlled-release fertilizers. If using water-soluble fertilizers, apply 75- to 100-ppm nitrogen with every irrigation or use 200 ppm as needed. Controlled-release fertilizers are commonly incorporated into the growing medium prior to planting at a rate equivalent to 1 lb. of elemental nitrogen per yard of growing medium. Plants grown under high fertility regimes generally become very lush and may take longer to flower.

Pests And Height Control

Although coreopsis can be produced relatively insect-free, aphids and whiteflies often become problematic. These pests can be controlled after they are detected, or they can be prevented using a proactive strategy. Preventative strategies include monthly spray applications of systemic chemicals such as Endeavor (Syngenta Professional Products), Flagship (Syngenta Professional Products), Marathon II (OHP), Safari (Valent U.S.A. Corporation) or TriStar (Cleary Chemical Corpora-tion) using the labeled rates for each product. These pests can be detected with routine crop monitoring; control strategies may not be necessary unless scouting activities indicate actions should be taken.

The most common disease observed attacking coreopsis is powdery mildew. Powdery mildew most commonly appears as small, white, talcum-like colonies on the upper leaf surfaces. To control this disease, it is best to manage the environment by providing proper plant spacing and adequate air movement and controlling the humidity, or if desired, following a preventative spray program using the appropriate chemicals. I have observed good results when rotating Compass (OHP), Heritage (Syngenta Prof-essional Products), Pipron (SePRO Corporation), Systhane (Dow Agro-Sciences) and Terraguard (Chemtura Corp.) for my preventative powdery mildew program.

With its compact habit, controlling plant height is usually not necessary when producing coreopsis 'Sunfire' under greenhouse conditions. Providing adequate spacing between the plants will reduce plant stretch caused by competition. If controlling plant height is necessary, several commercially available PGRs are effective when applied using the appropriate rates, frequency and timing. In Northern states, both B-Nine (Chemtura Corp.) at 2,500 ppm or Sumagic (Valent U.S.A. Corporation) at 5 ppm have shown adequate control of plant height when two applications are applied seven days apart.

Forcing

Producing flowering coreopsis 'Sunfire' out of season is relatively easy, provided a few guidelines are followed.

Most coreopsis cultivars have an obligate cold requirement for flowering, but 'Sunfire' does not and will readily flower without a cold treatment. However, there are no adverse affects when cold is provided.

'Sunfire' is an obligate long-day plant, absolutely requiring long days for it to flower. With photoperiods of less than 14 hours, plants will not flower. I recommend providing at least 14-hour photoperiods or night-interruption lighting when the natural photoperiod is less than 14 hours.

Growers can remove the lighting and produce plants under natural day lengths once flower buds are present. After visible bud, production under naturally short days decreases the overall height of the plant by reducing plant stretch. Removing plants from long photoperiods to naturally short day lengths will slightly reduce the number of flower buds produced and add a few extra days for the flowers to open. Waiting at least 7-10 days past visible bud to return the plants to natural day lengths will promote the development of additional flower buds and improve the overall appearance of the plant while it is blooming.

The time to bloom after the proper photoperiod is provided is a function of temperature. Coreopsis 'Sunfire' grown at 68¼ F will take 8-9 weeks to flower, while plants grown at 60¼ F will flower in 11-12 weeks. Warmer temperatures (above 70¼ F) will hasten plant and flower development and reduce the number of flowers produced. To obtain the best plant quality, I recommend producing 'Sunfire' at 65-68¼ F.

Availability

Coreopsis grandiflora 'Sunfire' is brought to the market by PanAmerican Seed Company. To obtain seed, contact any broker. Plug flats can also be obtained through various reputable perennial plug producers.