By Julie Christensen
Gardenias (Gardenia jasminoides), with their fragrant, waxy blossoms, rank among the queens of the flower garden. Unfortunately, they’re a bit tricky to grow – and that’s if you live in a warm climate. They won’t grow outdoors at all north of USDA plant hardiness zone 8 (but you can grow them indoors).
These attractive shrubs have glossy, evergreen leaves and grow 2 to 6 feet tall, depending on the variety. They grow best in full sun to partial shade, depending on your climate. In hotter inland areas, they definitely benefit from some afternoon shade. In foggy, coastal areas, they tolerate more sun.
Select a location for gardenias where they won’t compete with tree roots or sit next to the house, particularly on the south or western side. These areas tend to collect heat and remain warm at night, which can cause gardenias to drop their buds before flowering.
Amend the soil with plenty of compost, peat moss or manure. Gardenias prefer a rich, acidic soil that drains well. If you can grow azaleas, you can probably grow gardenias, providing that you live in a place with mild winters. Plant gardenias in the spring or fall and water them frequently during the first growing season as the roots become established. Thereafter, water as often as needed to keep the soil slightly moist. Gardenias don’t tolerate dry conditions.
Gardenias have shallow roots and don’t respond well to cultivating. Mulch them with a wood chip mulch, which will keep weed growth down, slightly acidify the soil and conserve moisture. Gardenias should be fertilized in early spring, as new growth emerges, and again in mid-summer. Don’t fertilize them after July — late fertilizing encourages lots of tender growth, which is vulnerable to damage from cold temperatures.
Prune gardenias after they’re done blooming. Remove the spent flowers, as well as any dead or straggly branches.
Iron Chlorosis occurs when the shrubs can’t access iron from the soil. Symptoms include yellowing leaves with green veins. Sometimes this occurs because the soil isn’t acidic enough. Acidic fertilizers and sulfur amendments can help. Gardenias can’t access iron when the soil is cold during the winter. In this case, the problem eases when the temperature warms. In both cases, an iron fertilizer can help.
Dropping buds/failure to bloom. Gardenias are finicky about temperatures. They bloom best with hot days and cool nights. When temperatures fluctuate wildly, or when evening temperatures rise above 62 degrees, the plants might drop their buds. Plant gardenias in a place where air circulates freely and they’re out under the open sky away from heat-collecting surfaces.
Insect pests. Whiteflies, aphids and thrips all infest gardenias and they’re most common during dry conditions. You might notice wilting leaves, webbing or a sticky substance on the leaves and ground. Mist gardenias in the morning to increase humidity. If the problem is severe, spray the leaves on a cool, cloudy day with an insecticidal oil or soap.
Root Rot. Wilting leaves and blackened stems and roots are caused by root rot, a fungal disease. The problem usually happens in heavy, wet soils. To prevent root rot, amend soils with compost or peat moss to improve drainage. Create a slight mound so the gardenias sit higher than the surrounding area. Remove and destroy any infected plants.
Growing Gardenias Indoors
Northern gardeners can grow gardenias as houseplants, but they need more care than most. Gardenias need bright sunlight, cool temperatures and consistent humidity. Meet these needs and you’ll likely have success.
Place gardenias in a room that gets plenty of bright light, such as one with a southern exposure. Water the soil frequently so it stays slightly moist, but not soggy. Run a humidifier in the room, especially in the winter, when the air is naturally drier due to heating systems.
Gardenias need regular fertilizing with an acidic fertilizer, especially during the active growing season. Fertilize them once every four weeks, or according to package directions.
Indoor gardenias won’t get as large as those grown outdoors, but they do benefit from regular pruning to remove old wood and faded blooms.
For more information, visit the following links:
Gardenia from Clemson University
Gardenia jasminoides from the Missouri Botanical Garden
YouTube has a short video on Gardenia growing tips and tricks.
Julie Christensen learned about gardening on her grandfather’s farm and mother’s vegetable garden in southern Idaho. Today, she lives and gardens on the high plains of Colorado. When she’s not digging in the dirt, Julie writes about food, education, parenting and gardening.