The Vintage hardy hibiscus line consists of two distinct series — Splash and Carafe — differentiated by their size at maturity. ‘Splash Pinot Grigio’ and ‘Splash Pinot Noir’ grow to 21⁄2-ft. tall. ‘Carafe Bordeaux’, ‘Carafe Grenache’ and ‘Carafe Chablis’ grow to 3-ft. tall.
Compared to other Hibiscus moscheutos cultivars, Vintage varieties feature a shorter growth habit; less need for growth regulators; full, uniform habits; and more flowers. They are available as actively growing starters (not dormant).
Flowers are dinner-plate sized, typical of the genus. Flower size is 9-10 inches with the exception of ‘Carafe Grenache’, which has 7- to 8-inch flowers. The Vintage hardy varieties come in red, white, pink or blush.
This schedule is based on production in the Northeast. Planting is best in late May through early June, with flowering in August through September. Climate in the South and Southwest can allow for earlier planting and, therefore, earlier finishing. Temperature is the primary driver. The first recommended plant date in the North is May 29.
Transplant rooted 72-cell liners into a well-drained media with a pH of 5.5-6.2. Use a reputable, well-aerated mix such as a perennial mix with composted pine bark. Plant so the top of the root ball is level with surrounding root media; place one pre-pinched, 72-cell liner into an 8- to 12-inch pot.
Never let the plants wilt from water stress. Begin a constant liquid feed with 150-200 ppm nitrogen from an N-P-K fertilizer where the majority of nitrogen is in the nitrate form. Examples include 20-10-20, 15-11-29 and 20-19-18. Fertilizers should contain micronutrients.
Long days are required for flowering: The minimum day length is 12 hours. Using lights to extend the day length to 16 hours or night interruption lighting from 10 p.m. to 2 a.m. with 10 foot-candles will speed flowering.
A minimum of 68º F nights is critical for successful flowering and timing. Planting in the North earlier than the end of May will require supplemental heat and, therefore, greenhouse space to ensure proper crop timing. Be sure to measure temperature at the shoot tips because bottom heat may not be enough. Once natural conditions hit the target temperature, the crop can move outside. If growing outdoors, do not be alarmed if temperatures dip below 68º F at night. Lower temperatures do not harm plants but can delay bud development.
Hibiscus may benefit from a preventative drench targeting Phytopthora after planting and a preventative spray for leaf spot when growing on. To prevent occasional fungal or bacterial leaf spot, overhead watering is not recommended. Take care not to let plants wilt as they grow larger because wilting will cause leaf loss and yellowing, along with flower and bud drop.
Routine scouting and preventative sprays for aphids, whiteflies and spider mites are beneficial. Watch for Japanese beetles on plants and buds. Orthene (Valent USA) and Sevin (Bayer Environmental Science) are effective for control but not eradication.
Growth regulators are not needed for 8-inch and larger pots with adequate spacing. If growing in smaller pots or tighter spacing, a growth regulator can be used for height control. Cycocel (OHP) is a good choice for most growers. Do not apply until the shoot length is about 1⁄2-1 inch long or after visible bud. B-Nine (Chemtura Corp.) can slow flowering, so only add it when Cycocel rates need to be above 750 ppm to control height. Use caution since high rates of Cycocel can cause burn. Timing of applications and concentration of chemicals will depend on the temperature of the crop.
One can expect an 8-week response time for flowering. Planting early in the season can slow response time, and planting later in the season can speed response time. Response time can also be variety dependent.
Continue constant liquid feeding as directed and maintain specific temperature and lighting requirements. Consider checking pH and EC levels. Recommended pH is 5.5-6.2. The EC level will depend on fertilizer formulation and water quality. If plants appear chlorotic despite fertilizer regime, check temperatures to make sure an average daily temperature of 68º F is being met. Lower temperatures can cause chlorosis.
Pots can be kept tight until leaves from neighboring plants begin to overlap. Space plants up to 21⁄2 times the pot diameter if leaves begin to overlap.