Help for purple verbena that's gone gray

July 11, 2009 

Q: I have some purple verbena, and it has been beautiful this spring. But it started to look grayish, so I cut it back. I cut it pretty short, and it killed all of it except one or two small bunches. What is the right thing to do when it starts looking tired and gray? I enjoy your column, and I learn something every time I read it. Thanks for the lessons on gardening. -- Sue Boykin

By "purple verbena," I'm going to guess that you mean a bedding plant like the pretty and popular Homestead Purple cultivar. You mentioned that it started to "look grayish," and I am wondering whether the plants were given plenty of elbow room in the garden, were well-mulched and are located in full sun. Not providing these basics allows powdery mildew a good chance to raise its ugly head, helped by poor air circulation, stress from dry conditions or too little sunshine. This fungus coats the leaves with a white powder, leading to a grayish look. When verbenas start to look tired and gray because of powdery mildew, I suggest that you yank the survivors up and start again, but this time provide a better environment for these beautiful bloomers.

Q: I read your column last month on peonies, and it reminds me of my question on this spring's lack of blooms from my irises. There were lots and lots of tall leaves, but only one bloom. There are five beds with more than 100 bulbs. In years past, I have separated bulbs as instructed. I have dug up bulbs and re-planted them to be certain of the depth, per instructions. No blooms. Please advise what to do for next year's desired flowering season. --Mary M. Delaney

Since you have had these iris beds for a while, I'm going to assume that they have bloomed well in the past but now have pooped out on you. So what is different now? My first guess is sunshine. Irises don't need semi-sun, occasional sun or filtered sun -- they need full sun for most of the day to put on a full flower show.

If your irises are close to any trees, it is a botanical fact that trees grow, so the location where these beds are could be getting less sun than it used to, and this would greatly contribute to the problem. Improper fertilizer is also a possibility. Normally, I would say too much nitrogen will result in lots of foliage but at the expense of blooms, but this is not the case with all irises, because beardless irises prefer a nitrogen-rich growing ground.

One other possibility is your soil's pH could be out of whack, which in these parts usually means the beds are too acidic. Take a soil test on the beds to determine not only the pH but also the nitrogen-phosphorus-potassium content.

L.A. Jackson is the former editor of Carolina Gardener magazine. Send your garden questions to him at askthegardener@newsobserver.com.

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