Use a well-drained, disease-free, soilless medium with a pH of 5.5 to 6.3 and a medium initial nutrient charge (EC 0.75 mmhos/cm with a 1:2 extraction).
Plug Tray Size
The recommended size is 200-cell or larger plug.
Cover the seed with plug media. Seed can be germinated in a germination chamber or directly on the bench. When germinated in a chamber, the plug trays should be moved out as soon as radicle emergence occurs, to prevent seedling stretch.
Germinate at 20 to 24°C (68 to 75°F).
Germination is slower but more uniform at the lower temperature range.
As long as the soil is kept evenly moist, high air humidity is not required for germination.
Light is not required for Stage 1
Plug Production :
Keep air temperature at 20 to 24°C (68 to 75°F) and soil temperature at 20 to 21°C (68 to 70°F) from germination to transplant.
Supplemental lighting is not required, but will decrease total crop time.
At radicle emergence, apply 50 to 75 ppm N.
Increase to 100 to 150 ppm N as leaves develop.
Keep soil media evenly moist.
Do not allow the seedlings to wilt.
Plant Growth Regulators
A Cycocel spray at 300 ppm applied 10 days after sowing can be used if needed. This treatment will reduce the plug height by about 50% and make the foliage darker green as compared to non-treated plugs.
(European Rate: 0.4ml/1, 75% a.i.)
Growing On to Finish :
Hibiscus is best suited to quart, gallon or larger containers (15 cm or larger). For quart and gallon containers (15-19 cm), use one plant per pot. For large containers (>19 cm), use 1 to 3 plants per pot.
Use a disease-free, peat-based, soilless medium with a pH of 6.0 to 6.5 and a medium initial nutrient charge (EC 0.75 mmhos/cm with a 1:2 extraction). “Nursery mixes” that contain soil can also be used, but may require an additional week of crop time and plants will have darker, green foliage.
Days: 21 to 30°C (70 to 85°F)
Nights: 18 to 21°C (65 to 70°F)
Warmer growing conditions result in shorter crop times. Do not allow average daily temperatures to drop below 68°F (20°C). Plants can become chlorotic and sensitive to pesticide spray (phytotoxicity) when grown at cooler temperatures.
Keep light levels as high as possible. Plants grow best under full sun. Space plants to allow light to reach basal area, as this promotes better branching.
Hibiscus requires a minimum of 12 hours of day length to flower.
Flowering is faster when day length is 14 hours or longer.
Supplemental lighting should be used under shorter days.
Keep media moist to wet. Consistent soil moisture is important and plants should not be allowed to wilt.
Growing plants too dry will result in flower bud abortion
Feed plants weekly at 200 to 250 ppm N in a complete fertilizer
Pinching is not recommended. Hibiscus branches naturally without pinching.
Best branching occurs when plants are spaced when the foliage touches the sides of the pot.
Plant Growth Regulators :
A tank mix of Cycocel at 750 to 1,000 ppm and B-Nine at 2,500 ppm has been tested in different climates in the U.S. and shown effective. Apply PGRs 2 weeks after transplant. Repeat application 2 weeks later if necessary. Optional treatment: Bonzi drench at a very low rate of 0.25-0.5 ppm with multiple applications (2 to 3 times) is also effective. Be careful when using Bonzi drench as it is very easy to stunt plants, especially for northern growers. If you are growing in a nursery mix that includes soil, less PGRs may be needed. One application 3 to 4 weeks after transplanting may be sufficient
PGR for Northern Europe
A weekly spray of a low concentration Cycocel (0.5ml/1, 75% a.i.) has been tested and shown effective in Risjenhout, Netherlands. If there is additional clay in the soil, it may turn out to be an alternative for the use of PGRs. To determine the best rate for your conditions, we recommend that you run an in-house trial.
Common Problems :
Insect: Thrips, aphids, spider mites. fungus gnats.
Use caution when using Adept, an insect growth regulator, as it could cause phytotoxicity on Hibiscus. To control fungus gnats, it is recommended to use Gnatrol or Distance as a drench for the larvae, and Decathlon or Talstar as a foliar spray for adults.
Disease: No serious problem.
Green Thumb Tips :
Plant Hibiscus in full sun locations (at least 6 hours of direct sunlight). Hibiscus can be planted in soil near ponds or water gardens. It will also tolerate dry conditions once it is established. When planted in a row, Hibiscus makes a hedge 2 to 3 ft. (60 to 90 cm) tall and about 2 ft. (60 cm) wide. Hibiscus can also be used in larger patio containers. Water and fertilize regularly with an all-purpose fertilizer for best results. If the foliage turns light green, it is an indication that plants need to be fertilized.
Hibiscus are perennial to USDA Hardiness Zone 5. Plants die back all the way to the ground in the Winter, then usually do not start growing until late May when the soil warms up. Overwintered plants will flower from mid-July on, with flowering decreasing in cooler Fall weather.