Gardening Q&A with Richard Nunnally

Q:Our Knock Out roses were a huge success this summer. However, I have no clue how to prune them. Should they have been pruned in midsummer to encourage more blooms? What should I do to them now?

Answer: One of the great fea tures of Knock Out roses is that they don't require a lot of pruning. I know several landscapers who believe you shouldn't prune them at all. They tend to continually produce new growth and new blooms throughout the season. Since yours were so successful, I wouldn't suggest changing very much. I prefer mine to stay under 5 feet tall, so I cut them back in mid-June. If you have room to let them grow, you'll just get that many more flowers. Should they wind up looking leggy at the end of the season, cut them back in late February to shape them up.

Q:Could you tell me if it is too late to prune an oakleaf hydrangea? I did it once in February, and it did not bloom that year.

Answer: It is too late to prune your oakleaf hydrangea. It should be pruned immediately after it finishes blooming. Since yours didn't bloom, you need to watch for others in your area, but they normally bloom in early summer. It's the new growth it made this summer that will produce the blooms next spring. When you pruned in February, you probably removed all of the bloom buds.

Q:I cut down a mimosa tree four or five years ago. Now I have shoots of mimosa coming up all over the yard. I cut them down with the lawn mower. However, I also have shoots coming up in shrubs, particularly in the middle of a rose bush that must be close to 100 years old. How can I get rid of these shoots without killing the shrubs?

Answer: Continuing to cut the mimosa sprouts where you can is the best way to deal with them. Eventually, the root system will starve to death and the sprouts will stop. However, where they are coming up in plant beds, you can cut them as close to the ground as possible and then immediately paint the herbicide glyphosate onto the cut surface of the stump. The herbicide will help kill the roots. Be sure to take the herbicide with you when you cut, because it has to be applied soon after the wound is opened.

Q:We have some land with a number of native dogwoods. In the past, I attempted to transplant one with no success. Can wild dogwoods be transplanted? If so, is there a trick to getting them to survive?

Answer: My experience transplanting native dogwoods has not been very good. They really need to be small, 2 feet tall or less. Their roots are shallow and very wide. Consequently, growing naturally, they don't have a compact root ball. Fall is a good time to transplant. However, another technique you might try is root pruning the tree now, and move it in late February. Root pruning involves making a slice all the way around the root ball as if you were going to move it, but don't. This cuts the roots and allows the plant to generate new roots at the point of the cut. That way when you move it, it has had several months to acclimate to a reduced root system, without going through the additional stress of relocation. I also stir a handful of superphosphate into any new planting hole to stimulate new roots.

Of course, I'd be remiss if I didn't remind you that there are some wonderful cultivars of dogwood available in our local nurseries and garden centers. A cultivated plant will allow you to start with a larger plant and make an easier transition to your yard.

Richard Nunnally is a freelance writer and host of WCVE's monthly gardening show, "Virginia Home Grown." He can be contacted at .