Why Are My Gardenia Leaves Turning Yellow?

In addition to the beauty and smell of the gardenia flower, its shiny, dark green leaves are a major selling point. So why are your gardenia leaves turning yellow? The yellowing leaves could be warning you of poor plant health. Before learning the possible causes and solutions to this discoloration, let’s find out exactly what growing conditions a gardenia prefers.

Gardenia Growing Needs

Failure to satisfy the growing needs of gardenias can cause yellow leaves. Gardenias prefer partial shade. They also have preferences for soil, including:

• Acidic soil: Gardenias prefer acidic soil, which helps them gain better access to nutrients. If the pH of the soil is alkaline, yellow leaves will develop. Keep soil between a pH of 5.0 and 6.0.
• Good drainage: Soggy soil can cause root rot in many plants, including gardenias. Gardenias need well-drained soil.
• Sufficient nutrients: Gardenias need plenty of nutrients, specifically potassium and nitrogen, from compost or fertilizer to grow flowers and foliage.
• Adequate moisture: Gardenias should be given about 1 inch of water per week. Keep the soil moist, but not soggy. Don't let the soil dry out before the next watering.

What Causes Gardenia Leaves to Turn Yellow?

Yellow leaves on your gardenias do not always indicate a problem. Come spring, it's normal to see some yellow leaves. This is simply part of the process of older foliage dying off to make way for new leaves.

Check first for signs of disease, such as the mold left by fungi, and insect infestations so you can rule them out or treat them immediately. Once you've ruled out diseases and insects, explore these other possibilities:

Chlorosis

Technically, chlorosis means a plant is not getting enough chlorophyll and suffering from a nutrient deficiency which turns leaves yellow. In the gardenia's case, yellow leaves may be a clue that the plant is suffering from a lack of iron, which is needed to help produce chlorophyll.

Send a soil sample to your local county extension and have them test it for iron deficiencies. The extension may recommend a solution. Usually, the soil will need to be amended to lower the pH.

Root Rot

Overwatering or growing a gardenia in soil with poor drainage can cause root rot along with yellow leaves. You will notice soft, mushy brown roots where there should be dry white or tan roots. If root damage has occurred, it may be too late to fix the problem so it will be best to replace the gardenia.

Nutrient Deficiency

In addition to an iron problem, there could be an insufficient amount of nitrogen or magnesium resulting in yellowing leaves. This is especially prevalent in older gardenia plants.

How to Fix Yellow Leaves on Gardenias

Don't assume you can simply fertilize to solve the problem. The issue may be that, although the required nutrients are present in the soil, the gardenia is unable to access them. This is why it's important to know what kind of soil pH your plant needs. In the case of acid-loving plants such as gardenias, if they are growing in a soil that's too alkaline, the nutrients they need (even if present in the soil) will be unavailable to them. To reduce soil pH and make it more acidic, you can use a fertilizer containing sulfur, for example.

If your gardenia is overwatered, you will notice dropping flowers and leaves that are wilted, drooping, or yellow. Thus, there is a need to pay attention to two of the other growing needs for gardenias: soil with good drainage and adequate (but not excessive) moisture. These conditions are closely related since soil with poor drainage is likely to be too wet even if you are not guilty of over-watering. Your goal in watering is to keep the soil evenly moist (right through the root zone); it should not be soggy. To prevent drainage problems, work a lot of organic matter into the soil.

Fertilizing

If you have ruled out incorrect soil pH, poor drainage, and over-watering as possible causes for yellow leaves on your gardenia, then you simply need to fertilize. Start with a balanced fertilizer unless you know for sure which nutrient is lacking, in which case you can become more targeted and apply a fertilizer high in the missing nutrient. Be careful to follow application instructions closely.