For size and showiness of azalea flowers, look at some Glenn Dale hydrids. (Photo by Sandra Leavitt Lerner/PHOTO BY SANDRA LEAVITT LERNER)

I have lilac bushes that do not bloom. This year, one bush has three or four purple clusters, another next to it has no clusters, and a third bush many feet away has about three white clusters. Several years ago, I pruned back some branches for more blossoms, but nothing happened the following year. The shrubs grow many leaves and are about 9 or 10 feet tall. At the end of summer I get powdery mildew on the leaves. The lilacs get about seven hours of sunlight. Should I amend the soil with something? What’s wrong?

The Washington region is categorized by the Agriculture Department as Zone 7. Lilacs will not flower well in this or warmer hardiness zones except in rare microclimates such as in frost pockets in low-lying areas. The way to have some success with lilacs is to plant them where they receive full sun, cold weather in winter, and mild weather with good air circulation in spring and summer. The oppressive heat of July and August in this region causes perfect conditions for powdery mildew; they will recover when leafing out next spring but produce fewer flowers. Common lilac prefers a neutral soil that has a pH of 6.5 to 7. A pH test from agricultural extension or a local garden center will indicate if you should add some pulverized agricultural limestone around the roots of the plant. Lilac blooms occur on stems that formed last year. Branches should only be pruned as flowers fade from these stems. Branches that have gotten large enough and have furrowed bark should be cut to the ground after blooming. New plants will grow from the roots.

I have tried several times to establish a decent rosemary plant in my Arlington yard, but the winters inevitably do them in. The nursery where I bought the last one assured me it would survive the winter. I planted it last spring, and now it’s dead. Where can I find a rosemary plant that will survive the winters here?

It is difficult to find the perfect location for a rosemary shrub to thrive in the Washington region. We have lost more than one in the years we have attempted to grow them. Locate the best microclimate for the plant and install a hardy variety, which we have found to be Arp. The best location we have found for it has been in a protected area within six to eight feet from the wall of the house or other heated structure, in full sun with well-drained soil. Ours gets eastern sun most of the day and is protected only during the last couple hours of afternoon sun, so it doesn’t experience wide temperature swings throughout the day. It is not an exact science. We planted additional rosemary about 20 feet from the house last year, and one of the four we installed has a green stem on it this spring. The others are brown, but we will give them a chance to push new growth before composting them. Most garden centers carry this herb.

For over 50 years, the daffodils on my west-facing, shaded hill have bloomed profusely. They have flourished despite being choked by ivy and have never been divided. This year, there are few blooms but plenty of healthy foliage. Do you have any suggestions?

Daffodils would definitely become crowded and stay small after 50 years of growth in the same location, ultimately failing to flower unless they are dug, separated from the parent plants, and replanted in a different area where they can collect nutrients independently. Daffodil bulbs cling to parent plants, growing so tightly together that they must compete with one another for nutrients. If you don’t want to start over by buying hundreds of new bulbs, dig and replant those that have become too crowded. When the leaves have yellowed or browned, dig and divide the bulbs. Take the largest ones and plant them separately. They will bloom again if they are large enough. The smaller offshoots might only grow foliage the first couple of years and then begin to produce flowers. During this time, photosynthesis occurs in the foliage, producing the nutrients needed for the bulbs to grow large enough to flower.

You can plant bulbs right after dividing them, but you have less chance of the bulb rotting in summer if you store the transplants in a cool, dry area with good air circulation and replant them in October. Discard bulbs that have a soft, pithy feel. Although not necessary, bulbs can be dipped in a fungicide before planting in fall to ensure they don’t develop rot. Follow all labeled instructions for use of fungicides.

We have been in our home for 11 years and have never had a good year of azalea blooms. Our neighbors have spectacular azaleas, and they don’t do anything to them. Some are merely inches away from ours and abound in every color. As the neighboring blooms start to fade, our azaleas will spit out an anemic display of flowers. Four years ago we replaced some with new shrubs — but still no blooms. Can you help?

Are your azaleas overgrown with ivy, in a heavily shaded area or being browsed by deer? If your answer is no in all cases, then you should try a different azalea variety. Some are much showier than others. Find the azalea you like, and purchase it when it’s in flower at the garden center. Try several that bloom at the same time and have colors that look good together. Some azaleas bloom in April; others flower in May and June. For size and showiness of flowers, look at some Glenn Dale hybrids or Girard hybrids. There is a repeat-blooming azalea called Encore that re-blooms in September/October. It is dependable, hardy and has proven itself in our garden. Be sure to buy them in bloom. Azaleas are a shallow-growing plant that will flourish in leaf mold or compost. They prefer acidic soil and must be kept moist when there is no rain.

As I drive near Lake Seneca in Montgomery County, I see many white dogwoods blooming in the woods. I don’t recall this abundance in prior years and am wondering if our area has not yet seen the full impact of anthracnose or if these might be survivors.

A favorite woodland tree of mine is the native dogwood. They flowered well this year and light up the forest in early spring. According to plant pathologist Ethyl Dutky from the University of Maryland, who has studied anthracnose since it was discovered on dogwoods in New York, Connecticut, Pennsylvania and New Jersey in 1983, the epidemic seems to be subsiding. There is another white-flowering tree that has also flowered profusely this year. I don’t ever remember seeing so many of them in bloom throughout the month of April. They are flowering pear trees — not native, but they have naturalized in this region and can be mistaken as dogwoods because of their bright white flowers. I noted them flowering in huge masses exactly where you described: the Lake Seneca area and along Interstate 270 in Maryland. The Washington region was one of the first areas to be invaded by these trees because the first breeding program to create hybrid flowering pears was developed in 1963 at the USDA Plant Introduction Station in Glenn Dale. The program was started with seedlings from Chinese seed, and the first hybrid was named Bradford pear. These trees are invading much of the East Coast and have proved to be prone to splitting easily. They are prevalent along highways and have naturalized in fields and along the edge of the woods.

Joel M. Lerner is president of Environmental Design in Capitol View Park, Md.