Gardenias at a Glance¹

Sydney Park Brown and Joan Bradshaw²

Description and Use

Gardenias are prized for their very fragrant white flowers and glossy, dark green leaves. This fact sheet provides a brief look at this popular plant. Many cultivars of Gardenia augusta (also known as Gardenia jasminoides) grow in Florida. There is considerable variation in plant and flower form and blooming time and duration. Depending on their size and form, gardenias can be used as hedges, ground covers, mass plantings or free-standing specimens. Enjoy their fragrance by planting them near patios or windows.

In Florida, gardenias are grown on their own root systems ("own root") or grafted on Gardenia thunbergia rootstock. Grafted plants are usually more vigorous and produce more and larger flowers than "own root" plants, but they are not cold hardy below 28°F.

Cultural Requirements

Light

For best flower production, plant gardenias in full sun, partial shade, or shifting shade. Prolonged shade may reduce flowering.

Soil

Gardenias grow in a variety of soil conditions in Florida, but they do best in well-drained soil amended with organic matter. They are not considered to be salt tolerant. An acidic soil pH between 5.0 and 6.5 is required or their foliage will yellow. Your county Extension office can provide information on how to take a soil sample and have it analyzed for pH.

Fertilization

Most established gardenias grow well with two or three applications per year. One application is normally scheduled around February (south Florida) or March (north Florida) and another in September (north) or October (south). A third application may be made during the summer.

A granular fertilizer formulated for landscape plants or an “acid-forming” product is suitable. Follow label directions. Ideally, 30-50% of the nitrogen should be slow-release. In south Florida or where soil potassium is frequently inadequate, a fertilizer containing 30-50% slow-release potassium should be used.

Pruning

Pruning should be done just after the plant finishes blooming. Vigorously growing plants can be lightly pruned and shaped up throughout the summer. Pruning after October 1st decreases next year's blooms.

Problems:

Yellowing leaves

If new leaves become yellow (chlorotic), a deficiency of a micronutrient—usually iron—is often the cause The primary problem causing the deficiency may be related to soil pH (the soil may not be acidic enough for gardenias) or root dysfunction due to nematode or disease infestation. Soil pH, nematode and disease problems are difficult to correct, so the best approach is to supply the nutrient in an acid-forming fertilizer or as a foliar spray. Some leaf yellowing on older leaves is normal.

Bud drop

Numerous stresses will cause green, unopened flower buds to drop. Dry, hot, or unusually cool weather, pests such as such as nematodes and flower thrips or cultural problems such as too much fertilizer or poor drainage can all contribute to bud drop.

Insects

Many insect pests attack gardenias in Florida and often warrant control. The most injurious insects include scales, aphids, spider mites, flower thrips and whiteflies.

Black sooty mold

This black, smut-like substance grows in the sugary secretion of sucking insects such as aphids, scales, mealybugs and whiteflies. Sooty mold is best managed by controlling these insects. Check with your local Cooperative Extension Office for the safest and most effective recommendations on pest management.

Nematodes

These microscopic pests attack the roots and cause premature wilting of the leaves and overall loss of vigor. No chemical treatments are available for nematode infestations on landscape plantings. The best practices are plant gardenias grafted on resistant rootstock (in central and south Florida) and to apply a 3-inch-thick, organic mulch.

Propagation

Gardenia can be propagated from cuttings or by grafting. Cuttings can be taken any time during the year, but they are most successful in June, July, and August. Root cuttings under continuous or intermittent mist, or in a pot covered with a plastic bag. The rooting media should be a 50:50 combination of clean, sharp builders' sand and peat moss; or a 50:50 combination of peat moss and perlite. In south and central Florida, graft a cutting of a desired cultivar to a rooted cutting or seedling of Gardenia thunbergia. This rootstock should be approximately 6 inches tall and pencil-thick.

For more detailed information see Circular 1098-Gardenias. This publication is available from your county Extension office or on the web at: http://edis.ifas.ufl.edu/MG336.

References

Gardenias. Circular 1098, Environmental Horticulture Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida.

Footnotes

1. This document is CIR1098, one of a series of the Environmental Horticulture Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date October 2007. Visit the EDIS Web Site at http://edis.ifas.ufl.edu.

2. Sydney Park Brown, Extension Specialist – Consumer Horticulture, Department of Environmental Horticulture and Joan Bradshaw, Extension Agent, Natural Resources, Citrus County. Institute of Food and Agricultural Sciences, University of Florida, Gainesville.

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.

Gardenias at a Glance1