The first place many teenagers encounter the gardenia (Gardenia jasminoides) is in long-lasting, sweet-smelling corsages. In U.S. Department of Agriculture plant hardiness zones 8 through 10, the plants, with their creamy blossoms and shiny green leaves, also grace Southern landscapes. The shrubs and their houseplant cousins present challenges to those who would keep them and enjoy their delicate fragrance from late March through mid-June, depending on cultivar. Gardenias suffer from several water-related problems that cause them to wilt.
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In their native ranges of China and south and east Africa, gardenias have adapted to warm, humid climates, acidic soil and light shade to full sun exposure. Give them an acidic soil with a pH of 5.0 to 6.5, amended with compost to aid drainage. Fertilize camellias from March to August with fish emulsion or fertilizer with a nitrogen-phosphorous-potassium composition of 3-1-2 or 10-5-15 for acid-loving plants. Commercial granular fertilizers or a water-soluble fertilizer call for mixing a tablespoon with a gallon of water -- half strength for houseplants -- and fertilizing before and immediately following bloom. Lack of humidity or use of unsterilized garden garden soil can cause wilting in young plants.
Waterlogged soil encourages root rot and root nematode growth, two causes of wilting. In both cases, badly infected plants must be discarded, but in cases where only a few roots are infected, pruning affected roots and up to one-third of the top growth along with a move to an area -- or re-potting -- with healthy or sterile soil might save the plant. No fungicide kills nematodes. Water gardenias to keep moisture even (neither dry or wet) to prevent root rot. Another option to moving a gardenia in the landscape is to plant it in a raised bed.
Whenever pruning affected plants, sterilize tools between each cut to avoid spreading disease to other roots and parts of the plant. Wipe surfaces of hand pruners or loppers, the long-handled pruners used on thick branches, with a 70 percent solution of rubbing alcohol and water.
Stalling Stem Canker
Wilting on one or more branches may be the result of stem cankers, a fungal disease caused by Phomopsis gardeniae. Again, the progression of the oval or elongated lesions can destroy a plant and it must be destroyed. When only one or a few branches are affected, they can be pruned out. Remember to sterilize equipment.
Try to do any pruning before Oct. 1, when plants begin setting flowers for the next spring.
Well-drained, evenly moist soil is a must for gardenias. Provide room for air circulation by planting them 5 to 6 feet apart outdoors, more for larger shrubs. Give houseplants a 2- to 5-gallon tub