Sprucing Up the Late-Summer Garden, Adapting to Shade and Battling Ivy

Chrysanthemums grow tall and leggy unless they are fertilized and pinched beginning in spring.
Chrysanthemums grow tall and leggy unless they are fertilized and pinched beginning in spring.
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By Joel M. Lerner
Saturday, September 6, 2008

As summer comes to an end, you're still busy in your gardens.

Q: We are having a gathering at our house, and the garden is looking tired. What can I do to spruce it up? -- Debbie M.

A: Use perennials. Some that should be blooming now: Helenium, in various colors and varieties, from late summer to frost, about three feet tall, sun preferred; Caryopteris x clandonensis"Heavenly Blue," an herbaceous, compact shrub, forming two- to three-foot mounds, in shades of blue with blooms from July into September in partial sun; chrysanthemums in a wide range of colors that can be used as perennials or annuals; and aster Symphyotrichum novae-angliae, which makes a good cut flower and prefers sun. Get an aster that is in bloom now since you want the color for your party. Dahlias are gorgeous and should bloom profusely until frost. (Deer probably like these best of the plants on this list.)

Even though the dahlias will probably return in spring, you may want to treat them as annuals used in full sun. Fill in with hanging baskets of annuals that are at their most floriferous.

Q: One of the questions you answered recently was about where the butterflies have gone. I have tried to use native species when I plant; however, my yard has lots of non-natives. I have seen one monarch all summer in my milkweed patch and little of any other species except for a few cabbage whites. Is there something else I can do? -- Mary R.

A: Continue to install native plants that are known habitats for the life cycle of butterflies. Nectar plants are the most ornamental for us to appreciate, but host plants where butterflies are born and eat as caterpillars are crucial to their survival. Give them fields and masses and clusters of host plants, and they will return. Habitat loss is the primary reason butterflies are disappearing. Roads, parking lots and even lawns don't provide what they require. Instead, install spice bushes, pawpaws, hackberries, hawthorns, sassafras, violas, hollyhocks and sunflowers.

Q: Which herbicide eliminates Boston ivy and groundcovers such as pachysandra and periwinkle?

-- David M.

A: To eliminate vines and groundcovers with herbicide, cut the plants back hard or dig out as much as possible. As they grow back, spray foliage with a systemic herbicide. Young growth is most susceptible. I have had success with Roundup and other glyphosate-based weed killers in the spring as vigorous new growth emerges. A second application might be required for complete control of well-established vines and groundcovers.

Q: In 2002, we planted two rhododendrons elegans, one in back, the other in front. Both areas are quite shady, and both plants died last year. I replaced them this spring. They turned black and died. What might be going on? What should I use instead of rhododendrons?

-- Richard M.

A: Rhododendrons need a more alpine climate and sandy, well-drained soil than much of this area has to offer. They seem to do well in microclimates around this region and west and north of Washington, in mountains and on the Eastern Shore. In very low sunlight, try Allegheny and chindo viburnums. Allegheny is semi-evergreen. Chindo is fully evergreen and, although it is Asian, doesn't flower and has no invasive tendency. A holly that I count on for shady sites is Nellie R. Stevens. These plants grow eight to 12 feet or taller.

Q: I have a plant I call resurrection lily. The stems are very tall, at least 18 inches, topped by a spray of lovely pale violet flowers. I just dug one up and potted it. Can it be grown in the pot, or must it be planted in the ground? -- Helen D.

A: Judging by your description of the flower and habit, you're correct. You have a resurrection lily. Another name is spider lily, because of the spidery spray of pale violet flowers. It's not actually a lily, but rather part of the amaryllis family. A more accurate name is spider or resurrection flower. It's usually pink, red, yellow or white. Because yours is violet, its probable botanical name is Lycoris squamigera var. purpurea. It likely will not survive the winter outdoors in a pot. In the fall, plant bulbs in full sun to partial shade, about six inches deep.

Q: The foliage has fallen off the bottom six to eight inches of my chrysanthemums, leaving a brown stem. The top foliage is green, and the blooms are fine. What can I do to have the green mound I once had? -- Linda D.

A: Mums naturally grow tall and leggy. Lower leaves fall off because they are shaded. Top parts that get sun stay green and flower. Mums grow back as perennials in the Washington region. They require specific cultural practices beginning in the spring so that they don't grow back leggy and leafless on the lower half. This is also the best the time to plant them.

Begin in spring with an application of low nitrogen fertilizer. Any general-purpose dry fertilizer with an approximate analysis of 5-10-5 is fine. Organic fertilizer is the best at releasing the nutrients slowly through the growing season. Sprinkle about two pounds per 100 square feet when growth begins. Fertilize again in May and June. Water in fertilizer. Stop fertilizing when flower buds form in July. Pruning or pinching accomplishes the mounded habit. When mums reach six inches, using your thumbnail and forefinger, pinch or cut off the top inch or two of growth on each shoot. This encourages branching. Pinch an inch every two or three weeks, always above a leaf. Continue until flower buds form in July. They will typically bloom from late summer to fall.

Divide your mums every two years. New roots and stems growing to the outside of the plant will produce your best plants for the next growing season. In spring, when new growth is one to two inches tall, dig up clump and tear or cut rooted pieces from the edges of old plants that have several young stems attached. Plant them and follow the cultural practices above. Inside woody center stems of the plant can be composted.

Q: In your Aug. 16 column, you said all ivy is rooted in the ground. Two months ago, my husband and I uprooted and cut all the ivy vines growing on our mature ash tree. Some vines had to be sawed because they were about five inches in diameter. We severed all vines and pulled down as many as we could. The ivy continues to flourish on all parts of the tree more than eight to 10 feet above ground. It seems to have taken root in the bark. Do we need an arborist to remove it? -- Sheila M.

A: On rare occasions, the adventitious roots on ivy can grow into the bark of trees. If enough leaf litter collects and decays in tree branches and there's enough moisture, it forms rich compost -- the perfect environment for most plants. This is one reason that you do not want vines to develop large woody stems holding moisture against trunks, rotting the bark and injuring the tree.

"Many people are surprised to learn that the ivy is rooted in the ground, not their tree," said Joan Furlong of Black Cat Ivy, a D.C. company that specializes in removing ivy from trees. "Although I've had one case thus far where some ivy stayed green because it managed to take root within a damaged tree." On the basis of her experience, I strongly recommend talking with a certified arborist.

Q: Can I cut the lowest or innermost layers of the "trunks" of cross-vines that have been growing on our deck for more than seven years? I have pruned away the older woody parts of the vines in one small section as an experiment as they are becoming unsightly as well as a great place for insects and other wildlife. -- Monica B.

A: Pruning cross-vine ( Bignonia capreolata) should be done on an as-needed basis annually. They flower on the current year's growth, so you can cut them hard and probably help their flowering and air circulation under your deck. It would be difficult to extricate one stem from another to selectively prune your vine. Renewing the plant a section at a time is a good idea. Do it in late winter before new growth begins. When you see how it renews, you will know how you need to prune it to encourage flowers and foliage. It's a tough, vigorous grower.

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.

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