Lots of plants in my yard are rapidly turning yellow. Such as, daylilies, iberis, roses, coral bells, and so forth. I think it's from the crazy weather. We had April in February here and then it got cold again. Lots of things froze in March(3 days of in the 20's ) I'm at a loss of what to do for these plants. a friend thinks a little nitrogen would help, but in all my years of gardening,(59 years) I've never had this happen before. Any ideas?