Green Scene

Beer vs. Slugs, Magnolia vs. Wind and Other Reader Quandaries

Give hellbores sun, and cut dead leaves in early spring to see the flowers.
Give hellbores sun, and cut dead leaves in early spring to see the flowers. (By Sandra Leavitt Lerner For The Washington Post)

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By Joel M. Lerner
Saturday, April 4, 2009

It's time to answer more of your gardening questions.

Q: What do you think about using beer to eradicate slugs when it is poured into shallow containers? -- Julie Snell

A: Beer is a good way to catch slugs. They are drawn to it more than any other animal to any other substance. Most other animals avoid it. Unfortunately, it is necessary to provide many pans of beer and dump a lot of dead slugs, and this will still not control the slug population. Use beer to monitor for a problem. If the pan fills up, you know another control is needed. Iron phosphate is more effective to control slug or snail infestations, and it will not harm pets or other wildlife.

Q: We have overgrown arborvitae about 30 feet high and want to trim them, taking eight feet off the top. Is this a good time of year to do this? -- Ron Dubois

A: Arborvitae will renew well if pruned now. When you prune, make sure to cut the bare woody center below the greenery that's around the outside of the tree. Prune the light outer growth to shape it narrower on the top and wider to the bottom to keep them full to the base.

Q: Our "Little Gem" magnolia has a bad case of wind damage; 90 percent of the tree has brown leaves. The healthy green leaves are on the lower part of the plant. The stem, when cut, seems fine, even far out on the limb. Is this tree dead? Will it come back? Do I need to prune drastically to get new growth? This was its second winter, and it seemed fine until those cold winds in February.

A: Michael A. Dirr's "Manual of Woody Landscape Plants" refers to this plant as moisture-loving and free-branching small tree or tall shrub that will grow stems and leaves out of thick, bare trunks when it defoliates. Southern magnolias should be planted in well-drained soil. They are hardy to zero degrees or colder, but I think the wide variations in temperatures in the Washington region in February were the cause for the dead foliage on your plant. Be patient. Most of the foliage should return. The large brown leaves are unsightly, but don't cut wood now. Allow new growth to be self-determining. When new branches and leaves emerge by mid to late summer, prune dead wood. Don't let the tree dry out in a drought, especially while it is pushing new growth.

Q: Is it possible to severely cut back Alberta spruce? I have several that have grown so tall that they are blocking my exterior doorway lights. -- Jim Shelly

A: No. They won't grow new needles. Dwarf Alberta spruce is a conifer. Conifers will not grow new foliage from bare stems. Therefore, they cannot be severely cut back like many broadleaf evergreens. The only way to control the size of conifers is to cut the candles (new growth) when they emerge in late spring to early summer. This is very time-consuming because of the tight habit and many growth points on dwarf Alberta spruce. Consider it to be a plant that should be replaced when it has outgrown its space. Look for plants that are about two to three feet smaller. They will be slow-growing enough to have the same appearance for many years without pruning, and they will be small enough that you can prune the candles annually to maintain their size.

Q: I need some recommendations on killing moss. It is growing in three different parts of my property -- the brick patio, flower beds and some areas of the lawn. -- Carl Roeth

A: Where moss is growing, it is often because it has the perfect conditions, usually moisture and shade. It will return, and controlling it will be an ongoing process. Improving air circulation, sunshine and drainage will help. For brick paving, use a power washer or hose to clean. Bleach mixed one to one with water will kill moss. Rinse brick quickly -- about 30 seconds. The mixture should not be allowed to run off onto plants or clothing. To kill moss in lawns, improve drainage and sunlight; aerate soil when dry; raise the pH by spreading about 80 pounds of horticultural limestone per 1,000 square feet; and use soaps such as Safer Moss & Algae Killer, which is potassium based, or Lilly Miller Moss Out for Lawns. (Keep the latter off paving to avoid staining it.) In beds, Moss Out Spot Treater, dry formula, will work.

Note: Chlorine bleach and ammonia can form a lethal gas. Ammoniated soap of fatty acids is labeled as a moss killer on walkways. Bleach is also recommended for control of moss on walkways. So read the ingredients and follow instructions closely.

Q: I love the moss that grows between my bricks. It is attractive and keeps weeds down. I often remove it because I am afraid that the moisture will deteriorate the brick. Can I keep my moss? -- Gayle Turner

Keep your moss. It does not deteriorate brick according to any information I have read, lecture I have heard or class I have taken. Some people like the appearance; others don't. That's the basis upon which to make your decision.

Q: We have four oak leaf hollies in the backyard that have been thriving. We just noticed that many of the leaves on the holly at the end of the row are turning gray/brown, and it looks like it will die. What could have caused this? -- Shayne Dizard and Bill Kojola

A: If you just noticed the browning on the holly, it could have been caused by the uncharacteristically warm spell followed by bitter cold days in February. That kind of weather will quickly desiccate a broadleaf evergreen in winter. I have noticed the same appearance on several of our established hollies. Allow several months for the plant to grow new leaves. If the branches are flexible, the holly could be a victim of this winter, and it will grow new leaves. The buds have just begun to swell on most hollies.

Q: What kind of maintenance do hellebores need, since their blooming time is winter? -- Marilyn Corn

A: This tough, evergreen perennial needs very little maintenance -- give them some shade to protect from sun and cut the dead leaves when they freeze in a winter like we just had. Maintain them in rich soil and moist, well-drained conditions.

Joel M. Lerner is president of Environmental Design in Capitol View Park, Md. E-mail or contact him through his Web site, http://www.gardenlerner.com.


© 2009 The Washington Post Company

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