answer:Gardening is an art and not a science. Be grateful that you have four healthy plants. That should give you a good yield. Same size pots? Same soil? Same amount of fertilizer. Any green leaves left? If so, cut off all yellowed foliage. If it is kaput, plant basil and other herbs or flowers for cutting. Truthfully, I have no idea. My two peonies, both bought at the same time and planted the same way next to each other are odd twins. One is a foot taller and twice as wide and has double the amount of blooms. Every spring I am surprised, both happily and sadly..My sis and I live four miles apart. My soil sustains acid-loving plants – hers’ alkaline.