Gardenias 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 a very simple reason: Few natural scents are as remarkable, evocative and memorable.
But the truth is that without the appeal of the spectacular scent, 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.
In the appropriate climate, gardenias can be planted in the garden in the spring or fall. They are generally planted from mature potted specimens that will bloom immediately. If you choose to try to grow gardenias from seeds, expect to wait two to three years before they flower.
Gardenias grow outside only in the USDA zones 8 – 11, across the South and the Pacific Coast. If you live in cooler climates, you can take your gardenia houseplant 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.
When planted in the garden, 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, as these plants don’t care for cultivating.
A well-tended gardenia will be compact with deep green leaves, and will 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. When growing them indoors, this means you’ll need to keep them in a room that’s relatively warm during the day.
Indoors, give gardenias bright light, but avoid direct sunlight, especially during summer. Outdoors, they prefer a part shade location.
Gardenias are acid-loving plants, so they prefer soil with a slightly lower pH. Normal potting mixes with a peat base meet this criterion. 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 mixed into the planting hole 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 & Humidity
Gardenias require temperatures above 60 degrees Fahrenheit. Avoid cold drafts if the temperature drops lower. These plants prefer a high humidity level, above 60 percent. In climates with cold, dry winter air, indoor plants may require the use of a humidifier or constant misting to maintain proper humidity.
For garden plants in warm regions, feed in mid-March using an acid fertilizer, then again in late June. Don’t feed gardenias in the fall.
For container plants, feed about every three weeks with an acidifying fertilizer—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 Gardenia
When planted in containers, plant gardenias in a good-quality peat-based potting mix. 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.
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.
Information courtesy of TheSpruce.com