December 2006

Rudbeckia fulgida ‘Pot Of Gold’ By Paul Pilon

Rudbeckia fulgida, commonly known as black-eyed Susan, is one of the most recognizable perennials in today's landscape. The popularity of the black-eyed Susan dramatically increased after the Perennial Plant Association named Rudbeckia fulgida 'Goldsturm' the 1999 Plant of the Year for its landscape performance and desirable characteristics.

Rudbeckia fulgida 'Pot of Gold', selected as a seedling from rudbeckia 'Goldsturm', is an improved selection of an already proven cultivar. Like its parents, 'Pot of Gold' delivers an impressive, long-lasting display of golden-yellow, daisy-like flowers with distinctive dark-brown central cones. The upright, branching stems are topped with numerous solitary, vivid, golden 3-inch blooms that are slightly larger than its parents.

'Pot of Gold' performs well across a wide portion of the United States throughout USDA Hardiness Zones 4-9 and AHS Heat Zones 9-2. This rudbeckia prefers full sun; although in the South, it performs best when some partial shade is provided. In the landscape, 'Pot of Gold' is slightly shorter than 'Goldsturm', reaching 20-24 inches high. Black-eyed Susan is an American native commonly used as accent and border plants and in mass plantings; it also makes an excellent cut flower.

Rudbeckia fulgida 'Pot of Gold' is a patented plant; self-propagation is prohibited at this time.

Production

Rudbeckia performs best when grown in a moist, well-drained medium with a pH between 5.8 and 6.4. Due to its large size when flowering, most growers produce 'Pot of Gold' in 1-gal. or larger containers. Each plug should be planted so its original soil line is even with or just below the surface of the new container's growing medium.

Water as needed when plants are young and becoming established. Once they are large, the plants will require more frequent irrigations, as they will dry out rather quickly. Under stressful growing conditions, such as warm temperatures and high light levels, they wilt very easily. Generally, if they are watered within a reasonable amount of time after they have begun to wilt, they will recover quickly if the water stress was not severe. In extreme cases, leaf injury, such as leaf necrosis or tip burn, may occur. When irrigation is needed, water thoroughly, ensuring the entire growing medium is wet or nearly saturated. It is best to only allow the growing medium to dry slightly between irrigations.

Black-eyed Susans are moderate feeders. Fertility can be delivered using water-soluble or controlled-release fertilizers. Growers using water-soluble fertilizers either apply at high rates (200-300 ppm) of nitrogen as needed or feed with a constant liquid fertilization program using rates of 75- to 125-ppm nitrogen with each irrigation. Controlled-release fertilizers are commonly applied as a top-dress onto the media surface using the medium recommended rate on the fertilizer label or incorporated into the growing medium prior to planting at a rate equivalent to 1- to 11?4-lbs. elemental nitrogen per yard of growing medium.

When marketing rudbeckia in bloom, height control strategies during production may need to be implemented to reduce plant height. Providing adequate spacing between the plants will reduce plant stretch ç caused by competition. Several of the commercially available PGRs are effective at controlling plant height when they are applied using the appropriate rates, frequency and timing. Compared to many perennials, the PGR rates needed to achieve sufficient control are relatively high. I recommend growers apply a tank mix of 2,500-ppm B-Nine (dam-inozide) plus 5-ppm Sumagic (uniconazole-p). For foliar applications, it usually requires two or three applications at 7-day intervals to provide adequate height control. Begin applying PGRs when the flower stalks are just beginning to elongate or bolt.

Pests And Diseases

Generally, rudbeckia can be produced relatively insect free. Occa-sionally, aphids and whiteflies will become problematic. Other insect pests such as caterpillars, four-lined plant bugs, grasshoppers, Japanese beetles, leafhoppers, mealybugs, spider mites, slugs, spittlebugs and thrips are also often observed feeding on rudbeckia but rarely become problematic. These pests can be controlled after they are detected and typically do not require proactive strategies.

Plant diseases may be observed when environmental conditions are favorable for their development. The most common diseases observed attacking rudbeckia crops are downy mildew and Septoria leaf spot. As with many perennials, the occurrence of plant diseases can be negated or greatly reduced when the proper cultural practices are followed. To control foliar diseases, it is best to manage the environment by providing proper plant spacing and adequate air movement, controlling the humidity, watering early in the day (which allows the foliage to be dry before night) and, if desired, following a preventative spray program targeting the pathogens using appropriate chemicals.

Forcing

'Pot of Gold' naturally blooms in mid to late summer. Flowering can be achieved throughout the year when following the guidelines discussed below.

Rudbeckia fulgida cultivars have a juvenile period where they will not flower until they are mature enough to perceive the treatments necessary for flowering. Plants that have at least 10 leaves will flower successfully, while those with less will remain vegetative, flower sporadically or take an extended period to reach bloom.

It is recommended to grow plants to maturity using short days or photoperiods no longer than 12 hours until the plants have an average of at least 10 leaves. Temperatures of 70-75¡ F will promote rapid development during this growth phase. Once they are mature and have been provided the proper photoperiod for flowering, they will develop an additional 12-15 leaves before the first flower bud.

Black-eyed Susans do not require cold treatment for flowering. However, they are considered cold-beneficial plants, as flowering will occur 2-3 weeks earlier following a cold treatment. Cooling (vernalizing) 'Pot of Gold' for a minimum of 10 weeks at 35-41¡ F is recommended. They can be vernalized as a plug or in the final container. Regardless of the container size, be sure they are fully rooted and past the juvenile stage prior to exposing them to cold temperatures.

They are considered obligate long-day plants, absolutely requiring long days for them to flower. With photoperiods of less than 13 hours, plants not receiving a cold treatment will not flower but remain as vegetative rosettes. If plants have undergone a cold treatment, flowering occurs when the photoperiod is greater than 13 hours. It is recommended to provide at least 14-hour photoperiods or night interruption lighting when the natural photoperiod is less than 14 hours.

The time to bloom after vernalization and the proper photoperiod is a function of temperature. When grown at 68¡ F, 'Pot of Gold' will reach flowering in 12-13 weeks; when grown at 60¡ F, it will flower in 16-18 weeks. To obtain the best plant quality, I recommend producing them at 65-68¡ F. Plants that have not been vernalized will take 2-4 weeks longer (depending on temperature) than the durations specified above.

Availability

Rudbeckia fulgida 'Pot of Gold' is brought to the marketplace by Darwin Plants; a limited quantity of plugs is available only from Darwin Plants. Finished containers may be purchased from many reputable finished growers or garden centers throughout the country.