Container Gardenia Leaves Yellowing and Falling

Q. I have a gardenia that is approximately four years old.  It blooms yearly and was doing great.  All of a sudden, literally overnight, the leaves turned yellow and are falling off. What has happened?  I water it daily, it is on the patio, outside where it has always been, in the shade.

A. I think your gardenia developed rot. The symptoms of root rot our yellowing leaves and leaf drop. Frequently the plant dies a relatively slow death unless it's in the heat, then it could be rapid.

            Container plants need to be repotted regularly. When we grow in containers, the soil organic matter (this is the component of the soil that helps keeps soil loose and gives good air exchange to the roots) begins disappearing at a steady rate. In a couple of years it will be in critical short supply.

            As this soil organic matter disappears, the open spaces in the soils that help with drainage and air exchange, diminishes. At the very beginning, a good container soil may contain as much as 50% of its volume as pore space.

            In about three years this pore space may drop to only 20 or 15%. Basically the soil collapses, losing its pore space. This might be okay for a palm growing in a container but gardenias need soils with lots of pore spaces.

            The soil becomes more dense, water drains through it more slowly, the soil stays wet longer, salts begin to accumulate and the roots begin to suffocate.

            Soil diseases attack the weakened roots, roots begin to die, leaves begin to yellow and drop from plant.

            Soils in containers need to be renewed every two to three years depending on the type of plant. Since gardenia is very susceptible to rots and grows much better in aerated soils, I would repot it no longer than every other year.

            If the Gardenia is not too far along in leaf yellowing and leaf drop, you might be able to save it. Go to your favorite nursery or garden center and purchase a good quality container soil, enough to refill the container. When you are there, purchase a chemical fungicide called Subdue. Subdue fungicide does a good job in controlling several of the root rot disease organisms. Applying a fungicide alone will not solve the problem so you must repot the plant as well. The plant can be put back in the same container if it is sanitized on the inside or use a different clean container.

            Remove the plant from the container during the cool temperatures of the morning and out of direct sunlight. Once the plant has been removed from the container, you must repot it quickly because the tiny feeder roots are continually dying after removal from the soil and drying out. Place the plant on a clean surface and gently wash the soil away from the plant roots.

            Thoroughly clean the container and sanitize the inside of it with a 200 ppm solution of bleach and water. This would be about on tablespoon of bleach in one gallon of water. Rinse the container and wipe out the excess with a clean rag or towel. Let it air dry in the sun for a few minutes to let the chlorine dissipate. Or use a clean, fresh container.

            Once you have removed as much soil from the roots as possible with water, you can repot the plant and use tap water to resettle the soil around the roots and remove air pockets. You will apply the subdue fungicide according to the label and water it into the soil of the repotted plant as a soil drench. Follow label directions.

Fertilize the plant as you would normally and watch for new growth to come from leafless stems that are still alive. Once a year or once every two years remove about one third of the soil from the container and add new container soil.