Gardenias (Gardenia jasminoides) are tropical broadleaf evergreens commonly grown as large indoor potted specimens for their fragrant white blossoms. The gardenia is a popular plant for a simple reason: few natural aromas are as unique, evocative, and memorable as the gardenias.
However, without the allure of the magnificent aroma, few gardeners would attempt to plant the high-maintenance gardenias, which are susceptible to various insects and diseases. Conservatories and greenhouses are the most usual places to find them. Even a few months in the company of a blooming gardenia makes them a worthwhile addition to your collection.
Gardenias can be planted in the garden in the spring or fall, depending on the environment. They're usually grown from mature potted specimens that bloom right away. Expect to wait two to three years for gardenias to flower if you grow them from seeds.
Gardenias can only be grown outside in USDA zones 8 to 11 in the South and along the Pacific Coast. If you reside in a cooler climate, you can bring your gardenia houseplant outside in the spring and summer after the temperature reaches 60 degrees Fahrenheit. However, bring it inside on any night when the temperature drops below that minimum, as well as as soon as fall arrives.
Gardenias prefer rich, acidic soil that drains well when planted in the garden. It's a good idea to amend the planting area with plenty of organic material. Gardenias should be grown in light to medium shade, away from tree roots, and in a spot where they won't harm them. To keep weeds at bay, cover the soil with a thick layer of mulch regularly. Weeds don't like to be cultivated.
When nightly temperatures are above 60 degrees Fahrenheit, and daily temperatures are between 75 and 82 degrees Fahrenheit, a well-tended gardenia will be compact with deep green foliage and bloom from early spring to summer, depending on the region. This means you'll need to keep them in a space that's relatively warm during the day if you're growing them indoors.
Give gardenias plenty of light indoors, but keep them out of direct sunshine, especially in the summer. They prefer to be in the shade when they're outside.
Gardenias like soil with a slightly lower pH because they are acid-loving plants. Standard potting mixes meet this requirement with a peat foundation. When planting outside, it's best to check the pH of the soil and amend as needed to give the plant the greatest possible environment. A teaspoon of agricultural sulfur sprinkled into the planting hole may assist in lowering the pH of the soil.
Maintain constant moisture in the soil, but reduce watering throughout the winter. Drip irrigation is beneficial because it keeps water away from the leaves, leading to fungal leaf spots.
Humidity and Temperature
Temperatures above 60 degrees Fahrenheit are required for gardenias. If the weather decreases, stay away from cold draughts. High humidity exceeding 60% is ideal for these plants. Indoor plants may need a humidifier or frequent misting to maintain moisture in locations with cold, dry winter air.
Feed acid fertilizer to garden plants in warm climates in mid-March, then again in late June. Gardenias should not be fed in the fall. Feed container plants with an acidifying fertilizer every three weeks—the type used for azaleas or camellias is an excellent choice.
Gardenias Come in a Wide Range of Colors
There are several varieties of this plant because it has been widely cultivated. Many gardenia plants are grafted onto a Gardenia thunbergia rootstock in warmer climates where they are grown outdoors. The grafted plants are more vigorous than the species, with greater, larger blooms, but they are even less cold tolerant.
Here are a handful of the cultivars that are recommended:
- Gardenia jasminoides (Gardenia jasminoides) 'Aimee' is a big shrub with magnificent 4- to 5-inch white flowers that grows up to 6 feet tall.
- G. jasminoides 'Fortuniana' is a big shrub that is noted for being one of the most prolific bloomers. From mid-spring until mid-summer, it produces 4-inch blooms.
- G. jasminoides 'Buttons' is a dwarf variety with 2-inch blossoms that grows 24 to 30 inches tall.
- G. jasminoides 'Crown Jewel' is a dwarf cultivar that grows to 3 feet tall and has 3-inch flowers. It has been reported to withstand temperatures as low as zone 6 in the north.
Gardenias should be pruned once they have finished blooming, eliminating straggly branches and wasted blooms.
Gardenia Potting and Repotting
Gardenias should be planted in containers in a good-quality peat-based potting mix. Repotting your gardenia in the spring or every other spring, as needed, is a smart idea. If it appears pot-bound or not as healthy as it once was, but you notice no insects or diseases, it's probably time to repot it. Use a rhododendron or gardenia-specific low-pH potting soil.
Rooting stem cuttings are the most significant way to reproduce gardenias. Take a 3- to 4-inch cutting of a stem tip in the early spring, just below a leaf node. Plant in a potting mix and perlite after dipping the cut end of the stem in rooting hormone. Maintain moisture until strong roots have formed, then transplant into 3-inch pots to continue growing.
Gardenias can be grown from seed, but it's a time-consuming process that takes two to three years to yield flowering plants. Seeds should be cleaned and dried for three to four weeks after being collected from dry seed pods. Plant the seeds in a perlite and peat moss mixture, with only 1/8 inch of potting mix covering them.
Keep the seeds moist and away from direct sunshine for four to six weeks until they sprout. Transplant the seedlings into pots filled with peat-based potting soil when they are several inches tall and continue to grow them in a bright indoor environment.
Typical Pests and Diseases
Insects, including scale, aphids, spider mites, mealybugs, and whiteflies, are the most common concerns, aside from cold temperatures and inconsistent watering. These can be treated with horticultural oils and washes, but expect your plants to be regularly infested. Powdery mildew, leaf spot, dieback, anthracnose, and sooty mold can all affect gardenias, and some of these diseases can be treated with fungicides. Affected plants will always need to be removed.
This plant is best suited for a gardener who appreciates the task of dealing with a fickle plant in exchange for magnificent flowers.