Late Spring Answers on Tulips and Training, Butterflies and Begonias

Can you include the zebra swallowtail the next time you write an article on butterflies? Its larvae feed on pawpaw tree leaves. Also, do you know a source for live native butterfly cocoons? -- Bill A.

The butterfly you have chosen as your favorite is a special one to find. This North American native is tough to see in its natural habitat in spite of its size -- a 3 1/2 - to 4 1/2 -inch wingspan -- because of its black-and-white coloring. Because pawpaw ( Asimina triloba) is the only host plant for it, every pawpaw grove needs its own zebra swallowtail butterfly brood. Some sources of information about butterflies native to the mid-Atlantic and Northeastern states are Butterflies and Moths of North America ( http://www.butterfliesandmoths.org), Susquehanna Butterfly Co. ( http://www.susquehannabutterfly.com), and Bear Mountain Butterflies ( http://www.bearmountainbutterflies.com).

You recommended buddleia to attract butterflies. We grew and loved it when we lived in the United Kingdom but found it to be terribly invasive in Silver Spring, even growing out of our neighbor's masonry retaining wall. It was very floriferous, and deadheading it would require a full-time gardener. -- Charles Y.

You reference a plant that has gotten a lot of attention now that it has naturalized on this side of the pond. It is indisputable that the plant attracts butterflies, but the attention is coming from its invasive tendencies. It is now listed among the top 20 invasive weeds in England, and we're not far behind.

My suggestion is to treat it as a woody perennial. Cut it back to about two feet high at the end of winter, before growth begins. This keeps flowers where they can be pruned (deadheaded) as flowers fade and before they go to seed.

What is the life expectancy of azaleas? I planted some about 35 years ago. Some have begun to yellow, and last year I lost one. I fertilize with Hollytone after blossoms die back. After yellowing began, I added iron. I've never seen insects on the leaves but noticed that the fertilizer doesn't seem to be dissolving, as if the ground has hardened. Can these azaleas be saved? -- Claire M.

Azaleas can live longer than 35 years, provided they get adequate moisture, organic material in the form of leaf mold and proper drainage. The drought last summer and fall was severe. If the problem has been caused by drought, the new growth should fill in with healthy leaves after flowering. Stop fertilizing, and focus more on providing good drainage. Water them if we have warm weather and no rain for a week to 10 days.

Old-growth azaleas are also known to succumb to one of two fungus diseases, phomopsis and phytophthora, that cause yellowing and dying of leaves. If that's the problem, the plants would succumb slowly, but it would become evident if you lose more plants. Contact your county Cooperative Extension Service and find out about diagnostic plant clinics in your area.

I would like to decorate my deck with potted plants. During the summer, the deck is mainly in the shade, with patches of sunlight. I'd like plants that will survive in containers outside all year. Can you make suggestions? -- Stuart B.

Consider planting a deciduous tree, several evergreens, and some perennial or annual flowers. Here are some plants that should grow well in shade to partial sun. All but the annuals should winter over and return yearly, weather permitting.

· Woody plants: Japanese maple, kousa dogwood, Little Henry Virginia sweetspire, emerald arborvitae, hetz midget arborvitae, dwarf falsecypress ( Chamaecyparis obtusa"Nana Gracilis"), golden variegated euonymus ( E. japonicus"Aureomarginatus") and wintergreen boxwood.

· Perennials: Rohdea ( R. japonica), liriope, hellebore ( Helleborus x hybridus), astilbe, Japanese painted fern, evergreen wood fern ( Dryopteris marginalis), bleeding heart ( Dicentra eximia"Luxuriant"), hosta, columbine ( Aquilegia canadensis), cardinal flower ( Lobelia cardinalis), hardy begonia ( B. grandis) and woodland phlox ( P. divaricata).

· Annuals: Coleus, impatiens, Joseph's coat ( Alternanthera), caladium, peacock ginger ( Kaempferia), elephant ear ( Colocasia), rex and tuberous begonias, and bacopa ( Sutera).

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