Gardenias are known and grown for their sweet-smelling white flowers and beautiful shiny, emerald green leaves. But yellow leaves on gardenias is one of the most common problems, and can be a sign of poor health. Here’s what you need to know.
Why do gardenia leaves turn yellow?
Chlorosis, or the yellowing of leaves on a plant, is a common indication that something is wrong with the plant and is stopping it from producing enough chlorophyll for the leaves to turn green.
With gardenias, a sudden change in temperature can often cause the leaves to turn yellow.
Mineral deficiencies are another major cause of chlorosis in plants and in gardenias the most common deficiencies are magnesium, nitrogen and iron. So, these deficiencies can result in gardenia leaves turning from a glossy green shade to a bright yellow.
Other causes of chlorosis
Chlorosis can also be caused by poor drainage, root problems, high pH levels, pests, disease or a combination of all of these.
In fact, another common cause of yellow leaves on gardenias is planting them in soil that is too alkaline. While people commonly try to grow gardenias as houseplants, they can be finicky as they require high humidity.
How to treat gardenias with yellow leaves
First, check your gardenia for other visual signs of distress, in case the issue is pests or a fungal infection that may require treatment.
Next, check the soil’s moisture levels. Over- or under-watering a gardenia can cause changes to the colours of its leaves.
If this isn’t the case, it could be a lack of nitrogen, magnesium or iron.
According to the WA Department of Agriculture and Food, if nitrogen is deficient, the oldest leaves will appear pale and lack the lustre of healthy ones. Yellowing appears at leaf tips and will affect all the leaves. Apply fertilisers high in nitrogen such as sulphate of ammonia or blood and bone. Organic matter and manures can also be added to the soil.
Magnesium is also essential for photosynthesis and the formation of proteins and chlorophyll. It moves freely within the plant and is taken from the older leaves to supplement new growth. A magnesium deficiency will affect the lower leaves on your gardenia first, yellowing them from the tip downwards. Dead spots may also appear.
To correct the deficiency, apply magnesium sulphate (Epsom salts) or dolomite (magnesium-calcium-carbonate).
A condition often referred to as lime induced chlorosis affects acid loving plants that are unable to take up iron in alkaline soils. The newer leaves become pale green, yellow and, in severe cases, white. Veins remain green. This is a common occurrence on coastal alkaline soils. To correct the deficiency reduce the pH of soil with ammonium sulphate or agriculture sulphur, and apply iron sulphate. A foliar feed with a complete liquid fertiliser will help correct this problem.
Tip! If you are going to prune, it is recommended not to use any gardening tool to removed the yellow leaves, instead, use your hands.
How to grow healthy gardenias
Most gardenias perform best in a well-drained, humus-rich, acidic soil in a sunny or partly shaded position. Water and feed well to promote lush foliage and heavy flowering. In cool climates or during winter time in Australia, they should be moved to a heated greenhouse, as most gardenias are frost tender.
