By Joel M. Lerner
Saturday, May 10, 2008
Washington's growing season is in full swing.
Q My wife loves tulips. Is it true they only last one to two seasons? Are there any species that come back every year? -- Gary S.
ATulips have a well-earned reputation of not returning for more than a year or two in this region because they will decay when their bulbs are left in the ground all summer. Some varieties, however, can better tolerate heavy soil and humidity. Drainage is the most important soil condition; you may even need to create a gravelly growth medium.
Several species to look for are the starry-flowered Tulipa tarda, white-and-gold; T. turkestanica, cream-and-yellow; T. batalinii Bright Gem, canary yellow; and T. praestans Fusilier, scarlet. They grow only six inches tall but make a good edging plant for early spring color. Plant in the fall.
Following your advice, I've had excellent results with Messenger on roses and phlox. Will it work on azalea petal blight? -- Bob B.
Messenger, an immune-system enhancer for plants, is labeled for petal blight and, through chemicals called harpins, will help your azaleas heal themselves. Apply monthly, beginning now, in the morning. Vegetation responds best if actively growing when you treat. Follow all labeled instructions.
For 15 years, my front yard has been overtaken by cicada-eating bees. I know they are beneficial, but what can I do to get rid of them? -- Jeanne M.
Cicada-killer wasps tend to be transient and move on in a few years. Because the insects have taken up residence for so long, they could be mining bees or digger bees. Neither mining bees nor cicada-killer wasps are aggressive.
Unlike the honeybee, mining bees are solitary. But large numbers of them may nest near one another if soil conditions are suitable. You should not treat mining bees because they are extremely beneficial insects of considerable importance in the pollination of many types of plants.
If you do have cicada-killer wasps, you can sprinkle Sevin (active ingredient carbaryl) around the holes in the evening, following label directions. This should kill them, though the process will take more than one season.
I never learned the basics of gardening, and I recently bought a house with a big yard and garden. Do you know of gardening classes in the D.C. area for novices? -- Bea
Check out basic horticulture courses or landscape-design classes at Montgomery College; Northern Virginia Community College; Prince George's County Community College; the University of Maryland; George Washington University Center for Continuing Education; the U.S. Department of Agriculture Graduate School; the county Master Gardener Programs; and through the Cooperative Extension System in Maryland, Virginia and the District. You can also contact local gardens to get on mailing or e-mail lists to receive information about their educational programs.
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.
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