How to Grow Gardenias in Hawaii

Gardenias, of the Rubiaceae (coffee) family, are a perennial evergreen. The shrub, which requires full sun and moist acidic soil, stands about 2 to 8 feet with thick, glossy green leaves and white, waxy, highly fragrant flowers. The gardenia blooms year-round in Hawaii, producing continuous flowers in areas that reach nightly temperatures of 60 to 62 degrees F.

Though there are over 200 species of the plant, three are native to Hawaii--Gardenia brighamii, G. mannii and G. remyi. While these species are now endangered, the most frequently cultivated gardenia in Hawaii is the Gardenia jasminoides, or common gardenia (native to China), referred to in Hawaiian as "kiele." Gardenia flowers are used frequently in Hawaiian leis.

Things You'll Need

• Sunny outdoor location with moist, rich soil OR 2-5 gallon pot
• Potted gardenia or gardenia cutting (any variety)
• Shovel
• Garden fertilizer
• Organic matter (if needed): peat moss, ground bark, compost
• Water hose or watering can
• Sprayer (small or large)
• Pruning shears
• Pest/disease controls (if needed)

Instructions

Selecting a Location for Outdoor Planting

1. Select a zone up to 2,500 feet in elevation.

2. Choice a site that has full sun exposure or filtered shade if area experiences intense heat.

3. Pick a planting area with rich, moist, acidic soil (pH 5.0-5.5) with reliable drainage and sufficient organic matter.

4. Select a position that is free from the competition of tree and other shrub roots.

5. Choose a spot with low salt deposits and is minimally affected by wind.

Planting Outside

1. Buy a potted gardenia plant with good root structure, of any variety, at a farm and garden store or use gardenia cuttings. Plant at any time of the year.

2. Add peat moss, ground bark and compost if soil is lacking in organic matter.

3. Dig a hole deep enough to cover the root ball but do not cover the bottom leaves of the plant.

4. Sprinkle in a small amount of fertilizer with a ratio of 3:1:2 or 3:1:3 of nitrogen, phosphorus and potassium. Fill over the fertilizer with soil.

5. Place the plant in the hole. (The plant roots should not touch the fertilizer.) Pack soil around the plant roots until the plant is stable.

6. Add 1/2-inch of mulch around the base of the plant.

Gardenia Care

1. Water the plant regularly, depending on elevation and rainfall, roughly three times a week. Keep it moist, but not saturated, at all times to avoid root deterioration.

2. Prune the plant when it looks scraggly, the branches are dead, or the flowers fade. Pinch back at growing points and wait until after the plant has flowered to avoid removing buds. (Pruning within the first year maintains compact shape and encourages heavy branching.)

3. Pick dying flowers so as to not attract bugs.

4. Fertilize after pruning. Do not over fertilizer, as it will burn out the plant.

5. Spray chlorotic, yellowing leaves with liquid iron supplement, available at garden stores.

6. Replace mulch when needed and do not cultivate around base of the plant.

Pest and Disease Control

1. Fumigate the soil properly prior to planting.

2. Buy approved spray insecticides, such as Malthion, Sevin or Diazanon if insect infestation occurs. Follow the directions on the label before spraying the plant.

3. Soak cotton swab in alcohol and rub it over the insect mass on the plant or spray the plants with a neem oil and water mixture to remove bugs naturally.

4. Take initial insect eradication steps to control infestation when sooty mold occurs. Wash the mold off with soap and water on a soft cloth.

5. Weed regularly and make sure there is good water drainage to help in air ventilation for dying foliage.

Indoor Potting

1. Buy a large 2 to 5-gallon pot. Fill the pot with equal parts topsoil to compost, to which garden fertilizer has been added.

2. Fertilize monthly with an acidifying fertilizer and water regularly to keep soil moist but not saturated. Do not let the plant dry out or sit in water.

3. Keep the plant in direct sunlight at least half a day.

4. Keep the room temperature at 70 to 75 degrees F during the day and 60 degrees F at night.

5. Re-pot the plant in a larger container if roots start growing out of the bottom.

Tips & Warnings

• For information on cuttings and/or grafting, how to transplant gardenias, or detailed information related to Hawaii gardenia pests and diseases visit the University of Hawaii-Manoa College of Tropical Agriculture and Human Resources website (see Resources).

• Use a drop of household plant feeder and Superthrive to small sprayers to aid in fertilization (use cap full for gallon sprayers).

• Coffee Cherry fertilizer is recommend.

• Read all labels on approved insecticides and pesticides before using.

• Avoid over watering or over fertilizing.

References

• Carol Christianson
• "UH--CTAHR"; Common Gardenia; Kent D. Kobayashi and Andrew J. Kaufman Tropical Plant and Soil Sciences ; May 2006

Resources

• UH-CTAHR; "Growing Plants for Hawaiian Lei"