Yellowed leaves on an indoor gardenia

(Question)

I have a gardenia that I have been growing indoors and out for 2 years. this year it has suffered from copious yellowing of the leaves and some leaf drop. I know that we have had a very dark November to February, and that is undoubtedly the cause of much of this. The plant is in the south facing window of a conservatory. It does continue to grow, and I hope that the increase in sunlight now will help.Any other suggestions?

(Answer)

The thought of a healthy flowering gardenia at this time of year is certainly enough to banish the winter blues. However gardenias can be quite temperamental and yours does sound like it might be in need of some assistance. There are many reasons that a gardenia might suffer from yellowing leaves (chlorosis) and some leaf drop which include low-humidity, over watering, insufficient light, root rot and over exposure to the salts in hard water, as well as insufficient levels of iron, magnesium or zinc. Yours may be suffering from a lack of light, as you suggested. Keeping it in the southern window should provide the maximum light available. Here are a few other things that might provide beneficial.

Watering should be reduced in the winter, when light levels are lower, to avoid root damage. If the water in your tap is very hard, the salt may build up in the soil. Take the plant to the kitchen sink and thoroughly flush the soil to wash out accumulated salts from fertilizer and deposits from tap water.

Gardenias are acid-loving plants that grow best in a soil with a pH of 5.0 to 6.0. Iron is an essential nutrient that plants use to produce the green pigment, chlorophyll. While iron is rarely deficient in soil, if the soil pH is above 7.0, the iron may be in a form that is not available to the plant. You could have the soil tested to check the pH level or you could repot the gardenia in a potting soil specifically made for acid loving plants to make the iron available. Over winter, you should feed with a balanced fertilizer at five or six-week intervals to provide needed nutrition.

Finally, to insure that there is adequate humidity for the plant, put a humidifier in the room or place the gardenia on a tray of pebbles and add water to the tray often to keep the pebbles wet. Don’t mist the leaves as this will cause fungus to grow on them.

Here are some great resources for gardenia care:

https://apps.rhs.org.uk/advicesearch/profile.aspx?pid=367

https://www.botanicalgarden.ubc.ca/forums/showthread.php?t=6838

https://urbanext.illinois.edu/focus/chlorosis.cfm

https://www.uri.edu/ce/factsheets/sheets/gardenia.html

I hope that your gardenia starts to thrive again soon.