Q. I have a gardenia that is approximately four years old. It has bloomed yearly and was doing great until all of a sudden, literally, about 75% of the leaves turned yellow and fell off. It is on the patio, outside, where his always been in the shade and I water daily.
|Gardenia with leaves yellowing.|
You didn't come out and say it but it sounds like the plant is in a container. When we grow in containers, the soil organic matter part of it (this is the part that helps keeps the soil loose and gives good air exchange to the roots) begins disappearing at a steady rate. It will be in a critically short supply by the third year. As soil organic matter disappears over time, the open spaces that help with drainage and air exchange, diminishes.
|Gardenia with dark green leaves, a sign of health.|
At the very beginning, a container soil may contain as much as 50% of its volume in pore space. Over three years this pore space could drop to only 20 or 15%. Basically the soil collapses, losing its pore space.
Collapsing soil becomes more dense, water drains through it more slowly, the soil stays wet longer, salts may 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.
This is why 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 not go 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 containing 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, repot it quickly because the tiny feeder roots die quickly when exposed to the air. 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 disappear. Or you can use a clean, fresh container.
Once you have carefully removed as much soil from the roots as possible, 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 every two years remove about one third of the soil from the container and replenish the container soil.