The Growing Medium for Gardenia

Growing Medium

• Plant gardenia in moist, fertile and well-drained soil for optimal growth. The shrub is intolerant of alkalinity and requires an acidic soil with a preferred pH of 5.0 to 6.5. When planted in alkaline soil, the shrubs are prone to suffer from nutritional deficiency, according to the University of Florida Extension. Amend your planting site with peat moss or compost prior to planting to improve fertility, and test the soil to increase acidity if required.

Improving Acidity

• The addition of ground sulfur and ferrous sulfate will help to increase acidity in soil with a pH over 6.0. Don't confuse these elements with aluminum sulfate. Adding 1.5 lbs. of ground sulfur per 100 square feet of soil will decrease pH from 6.0 to 5.5, or ½ point, as recommended by the American Rhododendron Society. In plants growing in sandy soil, add less sulfur at the rate of ½ lb. per 100 square feet (increase the amount for heavy clay soil). Also mix in ½ lb. of ferrous sulfate with sulfur per 100 square feet.

Effects of Alkalinity

• Gardenias and other plants that require acidic soil to grow well tend to suffer from iron chlorosis as iron becomes unavailable to the plants in alkaline soil. Symptoms of chlorosis include yellowing foliage with dark veins. With time, there are reddish spots on foliage, with brown margins and tips. A foliar spray made with 1 oz. of Epsom salts mixed in a gallon of water helps relieve the symptoms.

Fertilizer

• Apply a fertilizer specially formulated for acid plants to gardenias two to three times per year. Select a granular formula and make sure the fertilizer contains slow-release potassium and nitrogen. February and October are generally the recommended times to apply fertilizer. It is normal for the shrub to lose its oldest leaves during fall and winter.