The lure of fragrant white flowers have mid-South gardeners (zones 6 and 7) wanting to grow gardenias (Gardenia jasminoides). New cultivars, supposedly hardier than previous ones, hit garden centers every spring. Unfortunately, zones 6 and 7 winters usually prove them wrong.
Recent purchases of new cultivars ‘Frostproof’ and Pinwheel® and older selection ‘Kleim’s Hardy’ have proven disappointing here. Plants appear to dread wild temperature fluxes so common.
Native to semi-tropical areas of Asia (USDA hardiness zones 8-11), gardenias are slow-growing evergreen shrubs. Hardy forms supposedly may grow outdoors where winter temperatures are mild (zone 7, maybe 6). In most regions of the U.S., they should be brought indoors in winter and grown as a house plant.
Plant gardenias in an area to catches morning to early afternoon sun or all-day dappled sunlight. Protect gardenias from mid-afternoon sun. Gardenias prefer an acidic soil ranging from pH 4.5 to 6.0. Alkaline soil pH often causes chlorosis (interveinal yellowing) and reduces bloom count. Yellowing and shedding of older leaves occur before or after flowering. To increase soil acidity add elemental sulfur, chelated iron and/or aluminum sulfate. Lightly prune after bloom to shape and develop a dense shrub. Do not prune after mid-August.
Wherever you live, treat gardenias as finicky house plants. They’re troubled by spider mites, mealy bugs, scales, aphids and white flies. If you observe sooty mold growing on stems or leaves, white flies and aphids are likely feeding. Inspect plants often and spray with insecticidal soap or neem oil when pests are seen.
Plants are challenging to grow inside most homes and are best cared for a greenhouse or sunroom. Provide an east or south sunlight exposure over the winter months. Feed with a fertilizer for acid-loving plants such as Miracle-Gro™, Espoma™, or Daniels™ every 2-3 weeks in spring and summer. Allow plants to spend summer outdoors (mid-May through September in most locales) under the dappled shade of shade trees in your yard. From late fall through winter, feed plants monthly.
Overwatering is the greatest problem with growing gardenias. Plants don’t like their roots embedded in soggy soils. Repot gardenias in containers in late winter or immediately after flowering. Root pruning (removal of dead or browning roots) should encourage new roots.