I have a Gardenia plant in about 15″ diameter pot. Leaves are constantly falling. It blossoms but falls off plant. I spotted webs and spider mites. I used soapy water. It quickly killed them but the plant suffers worse each day. The ph is fine. I used fish powder, etc. Sufficient light. The humidity is fine- at least 50% in room. What’s wrong. Thank you. George
Gardenias are very difficult and demanding plants and rarely do well indoors. In general, they require cool temps in the 55-65 degree range when they are in bud. Warm temps cause the buds the fall off before opening. That temp range is cooler than most people will maintain in their homes.
In addition, Gardenias do not tolerate having their roots disturbed. You didn’t mention it, but I suspect you may have moved your Gardenia into a larger (15″) pot. It is quite common for people to move their new plants into larger pots and that is always a mistake.
Spider mites are an indication that your Gardenia was not grown in a quality nursery where adequate pest prevention measure are taken, In addition, spider mites multiply very rapidly when the plant is under stress for any other reasons such as improper light, temperature or watering. Treating spider mites with a soap solution is only effective long term if all leaf and stem surfaces of the plant are sprayed to the point where they are dripping wet. This is a messy job and most people are not as thorough as they should be with this treatment.
6-8 hours per day of direct sunlight, high humidity, and acidic soil (5.0 pH) are also important for maintaining Gardenias long term. The soil must be kept evenly moist at all times, but not wet. Water whenever the surface of the soil feels just barely damp. Avoid repotting until it is utterly potbound. Use an acid fertilizer, such as Miracid, at half-strength during the growing season, usually from March to October. But if you repotted, all bets are off because that changes everything!
Gardenias are extremely difficult to get to re-bloom successfully. When the flowers are finished, you can move your Gardenia to a sunny window and no longer worry about warm temperatures. In the fall, allow Gardenia temperatures to fall to about 50 to 60 degrees F. at night and no more than 70 degrees during the day. You must maintain these cool temperatures through the fall and winter if you want buds to set. Once buds form it is important to maintain temperatures in the 55 to 65 degree F. range or they will fall off. Of course, good light and careful monitoring of the soil to keep it moderately moist is also critical during this time. There are few things more disheartening than to see fat Gardenia buds fall off because the temperature got a bit too warm or the soil a bit too dry.
It is difficult for most people to provide these conditions. Some are satisfied to keep a Gardenia as a foliage plant.