Q: My plum tree has black crusty stuff on the branches. Bonnie Barnett, College Park
A: Your trees have black knot. It is common on plums and peaches in Georgia. The fungus causes a hard, black crust around twigs. Infection occurs from April through June, especially on the current season's growth. Remove all knots and swellings by pruning three to four inches below the knot. Plan a preventative spray of lime-sulfur or copper fungicide each year in winter.
Q: Not one of my Endless Summer hydrangeas bloomed this summer. What did I do? I've had them for several years and always a good show. Chris Blount, email
A: If they have good green foliage they will eventually bloom this summer. The problem might be some after-effect of the cold winter. Avoid pruning off new flower buds forming at the tips of stems now. And, in the spring, do not cut "dead" stems to the ground until new leaves have completely expanded, often not until early June.
Q: What are the beetles that gather by the dozens in magnolia blossoms? Are they harmful to the tree? Mike McKinney, Dallas
A: Magnolias are among the most primitive plants we use in our landscapes. Dinosaurs probably enjoyed their shade. They developed the organs we call flowers long before bees and butterflies came on the scene. As a result, magnolia flowers grew to attract a different kind of pollinator: beetles. Beetles love to eat magnolia pollen, so by visiting the flowers on nearby magnolia trees they accomplish the pollination vital for making magnolia seeds. Lots of different beetles visit magnolia flowers, all looking for a meal and inadvertently performing a valuable service.
Q: We have a beautiful new Atlas weeping cedar and it's doing well. I can't find any information about what to do if some of its limbs drag the ground. Carol Sanford, email
A: Rick Smith (www.pruningguru.com) says Blue Atlas cedar is an easy plant to prune. Usually you only need to prune the tips to approximately a foot from the ground. Make your cuts just beyond a side branch or a tuft of needles. If you have multiple branches that need removal, don't prune them all at the same height. This way the tree will look more natural and not manicured.
Q: On your show you mentioned serviceberry tree. Which variety is best? I would like a large variety as opposed to a bush. Mike Childers, Clayton County
A: Serviceberry is one of my all-time favorites. It has pretty flowers in spring, edible fruit and colorful fall foliage. I think you'd be pleased with either 'Princess Diana' or 'Autumn Brilliance.'
Q: I have hordes of tiny ants living in my outdoor potted plants. Are they a problem for the plants in those pots? Nan Straughn, Fulton County
A: Not usually, but I suppose an argument could be made that some ant species bring aphids to feed on plants near their nest. If the ants bother you, dilute any garden insecticide and drench the soil to kill the little critters.
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