From GPN - Greenhouse Product News
Very few perennials can compete with the impressive displays of color that hardy hibiscus cultivars provide when in full bloom.
- By Paul Pilon
Walters Gardens, Inc. has been working diligently with their breeding program over the past several years to select hibiscus with improved characteristics. Hibiscus ‘Summer Storm’ is one of their recent introductions that offers several improvements over existing cultivars.
‘Summer Storm’ produces an abundance of huge 8-inch blooms; each flower has large overlapping pink petals with a deep magenta eye that radiates out through the veins of the petals. Like many hibiscus cultivars, ‘Summer Storm’ blooms profusely; however, it blooms for nearly 12 weeks, which is twice as long as most of the cultivars in production today. In addition to its flower power, ‘Summer Storm’ has fantastic dark black–purple foliage; the darkest foliage on the market.
In the landscape, it grows to 4 feet high by 4 feet wide. ‘Summer Storm’ is well branched, which produces a fuller appearing plant and contributes to its extended bloom time. This cultivar is hardy throughout USDA Hardiness Zones 4 to 9. Although hibiscus is native to marshlands of the eastern United States, once established, they can withstand a wide variety of environmental conditions including drought and poor soils.
With its dark foliage, large flower size, and extended bloom times, ‘Summer Storm’ offers great appeal to container growers, retailers, and landscapers. Based on these attributes and strong garden performance, Proven Winners will be adding hibiscus ‘Summer Storm’ to its Proven Winner perennial program in partnership with Walters Gardens beginning this summer.
Hibiscus ‘Summer Storm’ is vegetatively propagated by tip cuttings by a limited number of licensed propagators and self-propagation is strictly prohibited.
Hibiscus are commonly produced and marketed in large container sizes; from 1 gallon up to 3 gallons in size. When growing 1-gallon containers, it is acceptable to plant one liner per pot; however, when they are produced in 2-gallon or larger sized containers it is best to use bareroot starting materials or to plant multiple (two to three) liners per pot. Liners should be planted so the original soil line of the plug is even with or just below the surface of the growing medium of the new container. When using bareroot starting materials, plant the crown just below the media surface.
Hibiscus performs best when they are grown in a moist, well-drained growing mix with good water holding capacity. They prefer to be grown with moderate to moist irrigation regimes. Never allow them to wilt or the plants may experience lower leaf loss and/or bud abortion.
To encourage branching and to produce fuller appearing containers, it is recommended to soft pinch hibiscus when the shoots reach 4 to 8 inches tall leaving four to six leaves on each branch. They can be pinched on multiple occasions if necessary. Allow at least six weeks from pinching until the desired bloom date.
During production, the pH of the media should be maintained between 6.0 and 6.5. Hibiscus are moderate to heavy feeders. Growers using water-soluble fertilizers either feed with a constant liquid fertilization program using rates of 100- to 200-ppm nitrogen with every irrigation or apply 300-ppm nitrogen as needed. Controlled-release fertilizers can also be incorporated into the growing mix prior to planting using the medium recommended rate or the equivalent of providing 1.25 to 1.5 pounds of elemental nitrogen per yard of growing mix.
The coloration of the foliage is greatly intensified when ‘Summer Storm’ is grown under high light intensities. Growing them during times of the year where the light levels are naturally low or inside greenhouses covered with poly will greatly reduce the purple foliage coloration. Plants grown outside in full sun will have the darkest leaves. Additionally, high light intensities promote better branching, result in more flowers per plant and produce shorter plants. To improve light penetration, promote better branching, decrease plant height and increase the number of flowers, it is best to provide ample spacing between the pots.
When producing hibiscus in containers, it is often necessary to control the plant height. Providing adequate space between the plants is the best and most effective method growers can implement to control plant height during production. If additional height control is necessary, plant growth regulators can be applied. Effective spray applications include the tank mixture of daminozide (B-Nine or Dazide) at 3,750 ppm and chlormequat chloride (Cycocel or Citadel) at 1,000 ppm or using paclobutrazol (Bonzi, Paczol and Piccolo) alone at 45 ppm. It is best to begin PGR applications about three to five days following a pinch and reapply them at seven-day intervals if additional control is necessary.
Insects & Diseases
There are a number of insect pests including aphids, caterpillars, Japanese beetles, mealybugs, scale, spider mites, thrips and whiteflies that are often observed feeding on hibiscus. Of these pests aphids, Japanese beetles, spider mites, and whiteflies occur the most frequently. Generally, hibiscus can be grown without the occurrence of diseases; foliar diseases caused by Alternaria, Cercospora, Myrothecium, Pseudomonas and rust may occasionally be observed under certain growing conditions. With routine scouting programs and upon early detection, these insects and diseases can easily be controlled with the appropriate fungicides or insecticides.
Growers should note that hibiscus are one of the last perennials to break dormancy in the spring. Be patient as they will begin to grow as the temperatures increase. When the soil temperatures are consistently above 60° F, they will break dormancy and begin to actively grow in approximately 10 to 14 days. When using vernalized liners, it is best to wait for them to break dormancy and begin to actively grow before transplanting them into the final container sizes.
Hibiscus requires long days for flowering. Growers should produce them during times of the year when the photoperiods are naturally long or provide long days with photoperiodic lighting when the days are naturally short. Since they require warm production temperatures, it is not always practical or economical to force hibiscus into bloom for early sales.
For optimum development, growers should provide 70 to 75° F day temperatures and 68 to 72° F night temperatures. Growing hibiscus with lower temperatures will significantly increase the production time and temperatures lower than 65° F may cause the foliage to appear chlorotic. The amount of time to properly schedule the crop depends on the factors mentioned above (photoperiod and temperature) and is also influenced by pinching. When a 1-gallon crop is not pinched and grown with warm temperatures and long days, it will bloom in eight to nine weeks. Pinching early in the crop will delay the flower time by two to four weeks; however, any mid to late season pinches will delay the time to flower by four to six weeks. In general, allow nine to 11 weeks for crops that are pinched one time early in production and 12 to 14 weeks for hibiscus that are grown in 2-gallon or larger containers and that have been pinched twice.
Keep in mind that it takes approximately six weeks from the time of pinching for hibiscus to reach flowering. Always look ahead at the desired sales date to determine if there is adequate time to pinch them back and reach flowering on a specific date.
Currently, hibiscus ‘Summer Storm’ is exclusively available from Walters Gardens, Inc. (www.waltersgardens.com) as 72-cell liners and No. 1 grade bareroot. As mentioned above, ‘Summer Storm’ will be marketed as a Proven Winner perennial through Walters Gardens as well as also being available through several Proven Winner propagators (www.pwcertified.com/grower/purchase/propagators.cfm) after July 2011.