Here are answers to some of your inquiries about the landscape. I hope they help to make your gardening experience enjoyable.

QHow do I eliminate a running type of grass (resembles Bermuda) that grows in an otherwise beautiful lawn? What is the best type of grass seed to use? I now use Rebel Supreme Super Blend Tall Fescue. -- D. Gillday

AThe only way to control Bermuda grass in an otherwise beautiful lawn is to kill desirable turf along with undesirable. You might have to repeat the methods more than once for complete control.

* Herbicide. Spray Bermuda grass with glyphosate, a nonselective, systemic weed killer, such as Roundup or Kleeraway. It will kill the roots and tops of all grasses. You can plant new turf seven to 10 days after spraying. After digging and raking up dead grass, seed or sod the spots and keep them moist through summer.

* Mulch. Cover trouble spots now with landscape fabric, black plastic or other material tacked in place with ground staples. This will block sunlight throughout the growing season and kill the grass in a mechanical, nonchemical manner. On Labor Day lift the fabric, loosen the soil, and seed or sod dead spots.

The best grass seed for this region is compact growing, turf-type tall fescue. The seed you are using is a good example of this type of blend. All turf should get at least seven hours of sunlight per day and be kept moist for the first couple of mowings.

Our azaleas are past their blooming stage and some leaves are mutating into a strange white ballish shape. Is this bad? -- Terry Forche

Your azaleas have a fungus called exobasidium gall (E. vaccinii). It causes thick, distorted leaves that produce a white powdery mildew. The most common condition for these fungal spores to grow in is moisture with poor air circulation.

Prune or pick the galls as they appear, leaving the healthy leaves. Clean up mulch and leaf litter under the azaleas in midsummer, and spread an inch of compost and a fresh veneer of ornamental bark mulch. They should do fine. Fungicide is not necessary, but if the galls are not removed the problem will be worse next year.

In your April 17 column, you wrote about VoleBloc, a kiln-fired, expanded slate, as a combatant to voles/moles. I'm awash in the varmints. They have destroyed gallons of fine plants from the roots up. I can't find VoleBloc. Can you suggest a specific garden center that carries it? -- Ann Briggs

Merrifield Garden Center and Meadows Farms show it in stock. You can also go to for more information and to contact the manufacturer directly.

I am looking for something to plant close to the house that will not threaten it, but will be visible when I'm sitting in the sun room. I'm looking for something that's slightly aromatic, attractive throughout the year and won't grow too large. My neighbors have erected a fence on top of a retaining wall that separates our yards, and their yard is slightly higher, so the wall and fence loom about 10 feet above my yard. That side receives pretty good western sun. Any suggestions what to plant along that fence? I have a one-foot swath of planting room in front of the wall. -- Maureen Nelson

You could attach a trellis to the house and plant spring flowering crossvine (Bignonia capreolata) or fall flowering sweetautumn clematis. If you prefer a tree, a columnar sugar maple (Acer saccharum Goldspire) would be tall, narrow and have gorgeous fall color. If you would prefer a shrub, a burkwood viburnum (V. X burkwoodii) will offer semi-evergreen foliage, grow to about 10 feet in height and have fragrant flowers in late spring. Plant the tree or shrub at least five feet from the wall of your house.

Use vines on the side of your property where there's a fence on top of a wall. A good combination of vines is Boston ivy (Parthenocissus tricuspidata) with a large flowering clematis, such as niobe, the president or a clematis from the jackman group, to entwine its way up the Boston ivy stems and flower through the green ivy in summer. The ivy turns maroon, offering color into fall.

Do you have suggestions for keeping birds off a balcony? They perch on the railing and make a mess. -- Naomi Glass

A company that specializes in bird repellents and offers several that might fit your need is Bird X ( It offers products such as Terror Eyes and Irri-Tape, netting, bird-proof gel, spikes, sonic devices and many other things.

Could you please address the issue of saving big trees? I continually see new construction of houses where they try to incorporate a huge existing tree or mature stand of trees in the landscape. Then dirt is piled up, construction equipment is parked, grading takes place all around the tree roots. Within a short time, the tree dies and has to be removed. -- Marcy Damon

Your point is well taken. To save big old trees, they must be protected from the impact of machinery, such as loaders and bulldozers, or heavy mowers rolling over the roots weekly. Compacting the soil and running over the delicate roots at the surface bodes poorly for tree survival. On even the oldest trees, the depth of absorption roots is a maximum of 24 inches, and they spread at least as wide as the canopy. The grade at existing ground level should never be changed under the canopy of a tree by more than an inch or two, and planting annuals under trees will cause you to disturb their feeder roots annually. The best way to treat these venerable members of our society is to keep their roots mulched with leaf mold, moist, well-drained and undisturbed to the width of their canopies.

We have a fungal problem in a bed of about 100 three-year-old irises. There is a two- to three-inch diameter, dark brown, fleshy (ear-like) fungal "cup" arising from the crown of several plants. The above-ground part of the iris lifts from the ground and is slimy at the base. I think we have a possible ascomycete fungus. Which fungicide should we use? -- Larry McDaniel

I will presume it is a bearded variety of iris. If so, ascomycete fungus (cup fungus) is often prevalent with excessive moisture, such as we have had the past 14 to 15 months. It is not worth trying to control this with fungicide.

The best cultural practice to control various funguses, and iris borers, is to improve drainage and divide plants regularly, discarding diseased and older stems that might contain borers. Replant only healthy one-year rhizomes, about four to five inches long, with a fan of leaves or two attached. Cut the fan of leaves to about four inches in height when transplanting. The best time to do this is in late June or July, right after blooming.

Plant rhizomes in full sun and a soil amended with about 30 percent compost. Use growth stimulants, such as fish emulsion, kelp, plant vitamins and humic acid, sold under many commercial names and formulas. Divide bearded irises every two to three years as the roots become dense and crowded. You will keep insect and disease problems to a minimum and the plants will continue producing showy flowers.

Note: When you dig irises, soil usually falls off the roots, and they divide rather easily. Dispose of all older root pieces and any signs of soft mushy plant parts. When you transplant them, locate in full sun, making sure that the eye or bud on the rhizome is at or within half an inch of the soil surface. Otherwise, it won't flower.

Why did my healthy, eight- to 10-year-old Cornus florida fail to bloom this spring? -- Jutta Paree

When a healthy, mature flowering dogwood (Cornus florida) fails to bloom, it is almost always because of low light. The dogwood is a shade-tolerant under-story tree in our woodland, but it needs sunlight. If possible, open the tree canopy overhead by pruning some larger trees shading it, and it should bloom again. Try to get it at least five to six hours of sunlight a day.

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