I am sorry for this delayed reply to your gardening question. The spring rush has brought a deluge of questions and we are working hard to catch up!
You are trying some good things. Check the soil moisture as extremes of wet or dry can cause such problems. Also, in your area the pH is too high for gardenia. Unless you plant them in a soil mix that is highly amended with peat moss and sand and also fertilize them with a product for acid loving plants, such as Miracid, they will likely show yellowing due to iron chlorosis. In a container it has a better chance or normal grow because the growing mediums is potting soil with a better pH level and high organic content.
Thanks for the question. Best wishes for a wonderful gardening season. Please stop in again soon!
Q&A Library Searching Tips