Fragrant and showy, gardenias are a common choice for both landscapes and gardens. Still, like most plants, these flowers are susceptible to damage from environmental and even microbiological threats. Brown leaves or brown spots on a leaf are a clear indicator that something is causing your gardenias serious distress.
Lack of Water
Water from the soil is not just the primary source of moisture for a gardenia but also the primary source of nutrients, picking up important vitamins and minerals from the surrounding soil and conveying them through the pores of the root system. While gardenias are tolerant of short dry periods, longer periods of drought can cause leaves and petals to brown from dehydration. If the soil gardenias are planted in is dry to the touch, water immediately to restore the plant’s vitality.
Although gardenias can thrive in a Mediterranean climate, they prefer high humidity and can suffer if the air is dry for long periods of time. Increase the local humidity around the plant by misting the above-ground parts of the flower with a water spray bottle.
Even a well-watered plant can wilt or brown if it does not get the right amount of nutrients. Gardenias require slightly acidic soil with a balanced mix of nitrogen, phosphorus and potassium, along with several micronutrients including calcium, magnesium and, in particular, iron. Feed gardenias in early spring during the growing season. Do not overfeed gardenias; too much nitrogen or potassium can burn roots and too much fertilizer can invite soil-borne infections.
Diseases and Pests
Slightly acidic soil fends off many soil-borne illnesses, but several microbial threats can infect the green parts of the gardenia. Powdery mildew, leafspot and sooty mold are only a few infections that can deprive a gardenia of energy and cause leaves to brown and wilt. Also, aphids, scales and spider mites can attack gardenia leaves, cutting them off from the nourishing stem. Spraying your gardenia with an antifungal agent such as horticultural oil with baking soda and insecticidal soap can reduce the risk of infection or infestation.
Gardenias are a temperature-sensitive plant that can suffer in long periods of excessive cold or heat. Sustained temperatures below 60 degrees Fahrenheit or above 80 degrees Fahrenheit can cause leaves to brown from stress.
- Medioimages/Photodisc/Photodisc/Getty Images