Asked April 15, 2021, 2:17 PM EDT
I have an above ground planter box where I have planted 5 peonies. The first several years (approximately 3) all of the plants do exceptionally well. After that time, The plant on the south end of the box begins to fail. It doesn't grow as well. It doesn't produce as many stalks, leaves, buds, etc. And, if it manages to produce a bud, that bud never blooms. It it like the plant only grows so big and then is stunted, shrivels and dies. However, every year the plant does grow back, only smaller and less healthy every year. None of the other plants in the box seem to be affected. There is no difference in water, fertilizer, weeding, etc. between this and the other 4 plants in the box. I see no evidence of slugs or snail damage. What could possibly be causing this and do I need to begin treating the other plants in the box with something to prevent this from spreading? Or do I just replace this plant every 4 years?
Washington County Oregon