Gardenias (Gardenia jasminoides) are tropical broadleaf evergreens, usually grown as large indoor potted specimens for the sake of their spectacular scented white flowers. The gardenia is a beloved plant for the very simple reason that few natural scents are as remarkable, evocative, and memorable. If not for this spectacular appeal, few gardeners would try to grow high-maintenance gardenias, which are vulnerable to many insects and diseases. They are most commonly found in conservatories and greenhouses. Nevertheless, even a few months with a blooming gardenia in the house makes them a worthwhile addition to your collection.
Gardenias grow outside only in the USDA zones 8 to 11, which range across the South and the Pacific Coast. If you live in cooler climates, you can take your houseplant gardenia outside during the spring and summer after the temperature stays above 60 degrees Fahrenheit. But be careful to bring it indoors on any night when the temperature falls below that minimum and as soon as fall makes its appearance.
|Botanical Name||Gardenia jasminoides|
|Common Name||Gardenia, cape jasmine|
|Plant Type||Flowering broadleaf evergreen|
|Mature Size||5 to 6 feet tall, similar spread|
|Sun Exposure||Part shade|
|Soil Type||Rich, well-drained soil; peat-based potting mix for container plants|
|Soil pH||5.0 to 6.5 (acidic)|
|Bloom Time||Seasonal bloomer|
|Flower Color||White, cream|
|Hardiness Zones||8 to 11; often grown as a houseplant|
|Native Area||China, Japan, Taiwan|
How to Grow Gardenia Plants
In warm climates, outdoor planting of nursery plants is best done in fall or spring. Gardenias prefer rich, acidic soil that drains well. Amending the planting area with plenty of organic material is a good idea. Place gardenias in light or medium shade, in a location where they don't face competition from tree roots. Soil should be regularly covered with a thick layer of mulch to control weeds rather than cultivating.
When planted in containers, plant gardenias in a good-quality peat-based potting mix.
A well-tended gardenia will be compact, with deep leaves, and bloom in early spring to summer, depending on location, when the nighttime temperatures are above 60 degrees Fahrenheit and daytime temps are between 75 and 82 degrees.
Give gardenias bright light, but avoid direct sunlight, especially during summer.
Gardenias are acid-loving plants, so they prefer soil with a slightly lower pH. With normal potting mixes with a peat base meet this criteria. When planted outdoors, it's best to test the soil for pH and amend as needed to create ideal conditions for the plant. A teaspoon of agricultural sulfur in the soil may help lower soil pH.
Keep soil continuously moist but reduce watering in the winter. Drip irrigation is a good method, since it keeps water off the leaves, which can cause fungal leaf spots.
Temperature and Humidity
Gardenias require temperatures above 60 degrees Fahrenheit. Avoid cold drafts if the temperature drops lower.
For garden plants in warm areas, feed in mid-March using an acid fertilizer, then again in late June. Don't feed gardenias in the fall.
For container plants, feed biweekly with non-alkaline fertilizer—an acid fertilizer of the type used for azaleas or camellias is a good choice.
Prune gardenias after the plants have stopped blooming, removing straggly branches and spent blooms.
Potting and Repotting
It's a good idea to repot your gardenia in the spring or every other spring as needed. If it seems to be pot-bound or not as healthy as it had been, but you find no insects or diseases, it usually is a good signal that it needs to be repotted. Use a low-pH potting soil formulated for rhododendron or gardenias.
Gardenias are best propagated by rooting stem cuttings. In early spring, take a 3- to 4-inch cutting of a stem tip, making the cut just below a leaf node. Dip the cut end of the stem in rooting hormone, then plant in a mixture of potting mix and perlite. Keep moist until good roots form, then transplant into 3-inch pots to continue growing.
Varieties of Gardenia
This plant has been widely cultivated, so there are many cultivars available. In warmer climates, where gardenia is grown outdoors, many plants are sold grafted on a Gardenia thunbergia rootstock. The grafted plants tend to be more vigorous, with better, larger blooms, but they are even less cold tolerant than the basic species. A few of the recommended cultivars include:
- Gardenia jasminoides 'Aimee' is a large shrub (up to 6 feet) with huge 4- to 5-inch white flowers.
- G. jasminoides 'Fortuniana' is another large shrub, known to be one of the most free-blooming. It produces 4-inch blooms from mid-spring through mid-summer.
- G. jasminoides 'Buttons' is a dwarf variety, growing 24 to 30 inches tall with 2-inch flowers.
- G. jasminoides 'Crown Jewel' is another dwarf variety, growing to 3 feet with 3-inch flowers. It is known to survive as far north as zone 6.
Common Pests/ Diseases
Aside from cold temperatures and inconsistent watering, which will cause bud and leaf drop, the most common problems are insects, especially scale, aphids, spider mites, mealybugs, and whiteflies. A variety of horticultural oils and soaps can treat these, but be prepared for your plants to face frequent infestations. Gardenias also are vulnerable to powdery mildew, leaf spot, dieback, anthracnose, and sooty mold, some of which can be treated with fungicides. In many instances, affected plants will need to be removed and destroyed.
This is a plant best suited for a gardener who enjoys the challenge of a temperamental plant that offers the reward of heavenly flowers.