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Q&A with Bob Polomski 9

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Extension Consumer Horticulturist, Clemson University

Should I be deadheading low-growing perennials like pinks and creeping phlox? They look somewhat ratty after bloom.

—C.P., Branford, CT

Answer: Deadheading, or the removal of spent flowers, improves the health and appearance of plants by channeling the plants resources away from seed production and into vegetative growth. Deadheading also prolongs the bloom period of certain perennials whose flowers open over many weeks. It may also encourage the production of a second, lighter flush of bloom.

Some perennials, especially low-growing, edging, or mat-forming types, benefit from being sheared shortly after flowering. This drastic form of deadheading involves removing spent flowers, stems, and leaves with a pair of hedge shears. It improves their appearance, encourages the production of attractive new growth, and prevents them from thinning out in the center. The following early-flowering perennials benefit from being cut back by one-half their height: lady's-mantle (Alchemilla mollis), rockcress (Arabis caucasica), snow-in-summer (Cerastium tomentosum), maiden pinks (Dianthus deltoides), many Geranium species and cultivars, sunrose (Helianthemum nummularium), evergreen candytuft (Iberissempervirens), deadnettle (Lamium maculatum), catmint (Nepeta xfaassenii), creeping phlox (Phlox stolonifera), moss phlox (Phlox subulata), wild blue phlox (Phlox divaricata), rock soapwort (Saponaria ocyrnoides), blue-eyed grass (Sisyrinchium angustifolium), and Hungarian speedwell (Veronica austriaca).

Keep your sheared plants well watered to help them recover and produce new growth. For more details on the fine art of shaping these and a great many other garden perennials, readers are advised to pick up a copy of The Well-Tended Perennial Garden by Tracy DiSabato-Aust (Timber Press, 1998). This excellent reference discusses not only deadheading but also the particulars of cutting back, pinching, disbudding, thinning, and deadleafing.

I've been trying to grow corn salad, or mache, but haven't been successful. What could I be doing wrong?

—A.R., Little Rock, AR

Answer: Corn salad (Valerianella locusta) has long been a popular salad green in Europe and is now appearing in North American restaurants, where it offers juicy texture and a mild, some say minty, flavor.

This very hardy cool-season annual is native to Europe, western Asia, and North Africa. It has been cultivated as an agricultural crop since the mid-17th century for its basal rosette with broad plantain-shaped leaves that are usually harvested when young. France is home to 75% of the world's mache production. Varieties include ‘Blonde Shell’, ‘Broadleaf Dutch’, ‘Broadleaf English’, ‘Coquille de Louviers’, ‘Grosse Graine’, ‘Verte de Cambrai’, and ‘Vit’.

Barbara Damrosch, market gardener and co-owner of Four Season Farm in Harborside, Maine, has been growing corn salad for years. She recommends sowing the seed in late summer or early fall in a sunny or partially shaded area, or two to four weeks before the last frost in spring. Avoid sowing seed during the summer, as hot weather causes erratic germination. Sow the seeds an inch apart or broadcast them into a bed.

Seedlings emerge in 10 to 14 days. Start thinning them when they develop at least three leaves, spacing them between two and six inches apart. When the leaves are about a thumb's length, harvest the entire rosette by running a sharp knife just below the soil surface.

Make successive sowings two to three weeks apart to extend the harvest. Damrosch harvests common corn salad throughout the winter months in Maine by cultivating the crop in low polyethylene tunnels. Farther south, the extra protection may not be necessary.

I have some old, overgrown, shrubby junipers. Can I trim them back to make them look fuller?

B.B., Renaker, KY

Answer: Yes. The best time to trim your junipers back is before new growth begins, although you can also do it now. Junipers possess latent, or dormant, buds along the length of their needle-bearing branches. Cut them back to where there is a green side branch or at least some foliage on the stem.

Avoid any heavy pruning of limbs or trunks where the wood lacks foliage.

In the future, you can ensure that new growth remains dense by removing a portion of the new growth on an annual basis. This will encourage profuse branching. If you are growing your junipers as a hedge, you may need to shear them two or three times a year.

My neighborhood improvement committee has asked me to look into trees for street planting. Can you tell me what to look for and some species to consider?

—T.L., Platteville, WI

Answer: Although the perfect street tree has yet to be discovered, there are species that are tolerant of urban conditions and capable of growing in confined spaces. However, when trees are completely surrounded by pavement, their life expectancy is typically only about 10 years from the time of planting.

The kind of tree you select will depend on the site. You'll need to consider the exposure, soil pH, and drainage, as well as the above and belowground space that will be available. Remember to factor in any utilities (such as power lines overhead and gas pipes underground), and nearby structures. Ideally, the tree you select will fit naturally into the space and not require continual pruning.

Avoid trees that produce messy or toxic fruit, thorns, shallow roots that lift sidewalks, or roots that will block sewers and drains. Also, do not select rapid-growing, weak-wooded species. The Bradford pear and the silver maple are examples of trees that suffer severe damage from winter storms. If deicing salts are used in the area, avoid salt-sensitive species such as sugar maples.

To make a list of appropriate street trees, start by asking whether your municipality has a street tree ordinance. Many of these include recommended species and varieties for your area. The Society of Municipal Arborists ( and the Wisconsin Arborist Association ( are also good sources of advice, as is the University of Wisconsin Cooperative Extension Service ( dex.cfm). Finally, you might consult the National Arbor Day Foundation (www.arbor, which has an online database with a number of useful links.

Wherever possible, plan on planting an assortment of different trees. This diversity will not only offer a range of forms, textures, and colors but will also be the best guarantee of their long-term well-being. So, of course, will a plan for the trees” care that extends beyond the initial planting.

How and when should one use a foliar fertilizer on plants? L.S., Lockwood, MT

Answer: Foliar fertilizer applications are best used as a supplement to a soil-applied fertilizer program. Miracle-Gro or Algoflash are examples of inorganic fertilizers that can be used for foliar feeding. Organic examples include fish emulsion, seaweed extracts, or a combination of both (such as Fertrell Liquid Fish & Kelp #3).

Applying liquid fertilizer to plant leaves is a rapid way of satisfying part of a plant's nutritional needs. It can also be a way to supply micronutrients such as iron, manganese, zinc, and copper, when their uptake from the soil is restricted. While foliar fertilizers will temporarily correct micronutrient deficiencies, a soil test is always recommended to determine the underlying cause of the deficiency.

The longer the nutrient solution is present in a fine, liquid film on the leaf surface, the greater the chance of absorption through the cuticle (or waxy leaf surface), and into the underlying cells. Therefore, apply foliar fertilizers on a cool, cloudy day or in the evening to decrease evaporation and improve their effectiveness.