I have a 20-year old peony. It’s always been beautiful, and bloomed profusely. For the last two years, it grows only about four inches tall, with one or two tall stems. This year it has one normal-sized stem with a bud at the top. The rest of the stems are four inches tall, and the the plant has stopped growing again. I have other peonies, and they are all growing normally. There is another peony growing about two feet from the crazy one, and is the same age. It is doing fine. Any ideas?