Gardenia shrubs are prized by gardeners for their highly fragrant flowers and bright, glossy, evergreen foliage that’s attractive year-round. When given the right growing conditions, these heat-loving shrubs will thrive. Choose the right place to plant a gardenia and give it the specific care that it needs, and you’ll be rewarded with romance and beauty.
Selecting the right variety
While all gardenias sport fragrant flowers, there are marked differences from variety to variety in mature size and bloom time. First decide what role your gardenia will play in the landscape. Will it be a centerpiece of a border or line a foundation with plenty of room to stretch out? Do you need a tidy, low, flowering border along a walkway or edging a bed? Are you trying to fill a large pot that will sit on a deck or patio? There is a gardenia variety to suit just about every landscape design need from compact smaller varieties that mature to 4 feet tall (such as Everblooming Gardenia) and others that top out at 8 feet tall and wide (such as First Love® Gardenia). Also, take into account blooms and bloom time. Some gardenias offer fewer but super-large 4-in diameter blossoms or while others have smaller, but more abundant flowers. By planting several gardenias with different bloom times it's possible to have a sequence of flowers from May through August.
- Zone: Gardenias are subtropical plants that thrive in warm, humid weather. Most gardenias are hardy in zones 8-11, though a few varieties hardy to zone 7 have been developed (Kleim's Hardy gardenia is one), and a few are only hardy in zones 10 and 11 (including Double Tahitian gardenia).
- Soil: Gardenias require a soil pH of between 5.0 and 6.5, which is considered acidic to slightly acidic. It's wise to take a soil test with a simple kit available at nurseries and home-improvement centers. If the soil pH is too high, amend with sulfur, which is available in a variety of chemical forms. If possible, amend the pH up to six months or a year before planting to allow the application to work. In addition to the right pH, the best soil for gardenias will be a lightweight and full of organic matter with good moisture-retention properties. If your soil is heavy and clay, or very sandy, amend with copious amounts of compost. If planting gardenias along a house's foundation, test the pH; soil around the foundation can have a much different pH than soil in the center of the garden.
- Moisture: Constant moisture is non-negotiable for gardenias. They’re not drought-tolerant, but they also don’t want soggy roots. It’s essential that you site them in an area with well-drained soil. Organic matter helps retain moisture at the level the shrubs need. Too much clay can lead to waterlogged soil while overly sandy soils dry out quickly and don’t retain nutrients.
- Light: Gardenias can handle full sun, but need protection from baking midday or afternoon sun in higher growing zones. North and east-facing exposures are ideal because they will receive bright morning light and some midday light, but won’t be in full sun all day or during the absolute heat of the day.
The best times for planting are fall and spring when temperatures are moderate. If growing in a colder zone, plant in the spring so that plants can root in well before the fall. Gardenias, much like camellias, like to be planted a little high. Dig a hole that is twice as wide and just as deep as the plant’s rootball. Firmly pack 3-4 inches of soil at the bottom of the hole and place the plant in it. Backfill with the same soil that you removed from the planting hole—do not mix compost in. Finish by mulching with compost, taking care not to mound it around the stem. Renew this mulch layer every fall to protect the plants during the winter and spring to control weeds.. Avoid cultivating around the root zone of gardenias once they are established. They do not like to be disturbed. It’s better to hand-pull weeds or mulch.
Gardenias grow best when they receive at least one inch of water per week. If your area is not receiving that in steady rainfall, water deeply once a week.
Check the pH to make sure it’s in the desired range of 5.0-6.5 before fertilizing. Apply a slow-release fertilizer formulated for acid-loving plants in the mid spring and mid summer.
Prune gardenias to maintain size in the summer after they finish blooming and throughout the year to remove dead or diseased growth as necessary. You can prune the shrubs hard after blooming, but they may not flower as profusely the next year. Gardenias, used as a hedge, will tolerate shearing, but you'll risk sacrificing blooms and encouraging dense growth that serves as a home for fungal diseases to thrive. There are better plants to use for a formal hedge. (They’re great for informal hedges, though.)
- Sooty mold: Sooty mold is a gray, fuzzy mold that covers the plant leaves and is a symptom of a whitefly or aphid infestation. Rid plants of those pests using insecticidal soap and mold will recede.
- Bud drop: Lack of adequate water during the summer can cause bud to drop so it’s important to always irrigate during dry weather. Lack of sunlight can also lead to bud drop or even cause the plants not to form flowers. Finally, insect problems from aphids or whiteflies can cause bud drop. Eliminate issues one by one, and you’ll have a gardenia covered in blooms.
- Yellowing leaves: Root rot can lead to yellowing leaves. Try to pull the plant up. If it come s out of the ground easily and the roots are mushy, root rot is the culprit and the plant should be discarded. Iron chlorosis (iron deficiency) causes yellow leaves; adjust the soil pH and, possibly, apply a foliar feed of iron.
- Failure to set flower buds: Usually when a gardenia flat out won’t produce flower buds it is growing in too much shade. Move it where it will get more sunlight. Sometimes an aggressive late summer pruning will interfere with flowering as well.
Growing Gardenias Indoors
Gardenias are not indoor plants, despite the fact that they are often sold in the florist trade as such. Two limiting factors to indoor gardenia health are light and humidity. It is almost impossible, without a greenhouse or sunroom, to get the plants enough sunlight for them to set and retain flower buds. Sometimes indoor gardenias will grow flower buds, but the buds will drop before opening. Placing the plant in a south-facing window that protrudes slightly so that sunlight reaches the plants on three sides will give you the best chance of success. To elevate humidity, use a humidifier placed near the plants in the room where the plants are growing. Misting the leaves is a temporary relief, and can encourage spread of fungal diseases.