Most of us growing Gardenia jasminoides and other varieties look forward to their intoxicating fragrance. The flowers of many Gardenia varieties look like creamy white roses. Plus the Gardenia shrub is a beautiful plant.
But, there are times when growing this acid-loving plant we see leaf yellowing. The green leaves show their nutrient deficiency, pests and disease problems.
Gardenia plant leaves do yellow from time to time during healthy conditions. When this happens investigate possible causes and find the proper solution.
Likely culprits include Powdery Mildew, Iron Chlorosis, Root Rot, Nematodes, and Stem Cankers.
What Causes Yellow Leaves On Gardenias?
Expect to see yellow leaves on gardenias in early springtime. These yellow leaves will drop in preparation for new growth.
Yellowing leaves after new growth has established itself could be a sign of disease or pest infestation.
What Damage Do Yellow Leaves Cause?
Yellowing leaves are not always a sign of permanent damage. But some causes can lead to permanent damage if not caught early on.
Below we share some of the reasons Gardenia leaves turn yellow along with a remedy.
Powdery Mildew – Yellowing Leaves From Fungal Disease
One enemy is the powdery mildew fungus aka Microsphaera polygoni. It first appears as a gray or white powder in small patches or dots on the leaf surface.
Powdery mildew is most prominent during warmer months. If left untreated it can darken and produce reproductive structures on the plant.
This fungus causes leaves to turn yellow, become deformed, and eventually fall off. It can also cause deformation of the flower buds.
How To Control Powdery Mildew On Gardenias
The first step is to prune away infected stems.
This fungus loves humidity. Increase airflow through the plants by pruning crowded limbs and moving potted plants farther away from each other.
Fungicides are an excellent preventative treatment for this condition also. Apply the fungicide at the first sign of the mildew to prevent further damage
Iron Chlorosis A Sign Of Nutrient Deficiency
Iron chlorosis is an iron deficiency of the acidic soil surrounding the gardenia plant either growing in the ground or as a potted Gardenia.
Iron is crucial for the production of chlorophyll, which causes the green pigment. A lack of it causes Gardenia leaves to yellow.
Newer leaves may turn yellow except for the veins. Older leaves may have touches of yellow on the outside of the leaves.
An iron pH level above 7 makes it difficult for the gardenia to extract the amounts it needs.
Learn more about Gardenia Fertilizer
The Fix For Iron Chlorosis In Gardenias
Gardenia plants need a soil pH level between 5 and 6 to absorb needed nutrients well. Anything above that restricts the kinds of nutrients it can absorb.
If you suspect an iron deficiency, test your soil to confirm.
Apply iron chelate for plants to the soil or leaves as a foliar spray.
Or mix ferrous iron sulphate with a few drops of soap in a gallon of treatment. Apply to the leaves often throughout the growing season at the first sign of iron deficiency. Iron will help the leaves turn green.
A magnesium deficiency can lead to yellow leaves on gardenia plants.
Root Rot The Result Of Too Much Water
Another common culprit, root rot occurs when roots of your Gardenia plant have too much water.
Older leaves begin to yellow, wilt, and then leaf drop starts. The plant’s roots will be brown, missing, or rotten.
In a healthy gardenia plant, the roots should look white and not too moist. Poorly drained soil or too much overhead watering will create an environment rife for root rot.
Gardenia Root Rot Less Water Or New Location
Of all the causes of yellow leaves on gardenia plants, root rot may be the simplest to solve. Cut back on your watering schedule so that your roots don’t become waterlogged.
For increased drainage transplant your gardenia to a new location with better draining soil or to a raised bed.
You may notice the leaves on your gardenia wilting during hot weather or displaying a yellow spotting pattern.
This may be a sign of nematodes. They are tiny roundworms invisible to the human eye that nibble away on a gardenia’s roots.
Take a soil sample and have it analyzed to know for sure.
Nematodes are one of the reasons many gardenias are grafted onto Gardenia thunbergia rootstock.
Nematodes Remove and Destroy?
Nematodes can be pesky to get rid of. The best treatment is to provide your gardenia with frequent fertilization and watering.
Also, cut back infected branches, or remove and destroy highly infected gardenia plants.
Stem Cankers Sunken Oval Lesions
The fungus phomopsis gardenia is the culprit behind stem cankers. It causes long sunken oval lesions that darken along the stem.
The fungus thrives in humid environments. It enters the plant through the wounds and overwinters inside.
The result is yellowing leaves that wilt and eventually drop. If left untreated, the fungus will stunt the gardenia plant’s growth.
Stem Cankers Saving The Plant May Be Difficult
Treat stem cankers by cutting out the infected stems. Saving the plant may be impossible. Then track the amount of water and fertilizer you’re giving your plant.
Don’t over-do it or deprive it, either. Wash your plant with a 10% bleach solution in areas that do not have cankers to get rid of any spores.