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Q&A with Bob Polomski 29

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Extension Consumer Horticulturist, Clemson University

I am a little confused about bulb planting depths. I understand that different species need to be planted at different depths. But what happens in nature? When these plants reproduce by seed, how do the bulbs magically end up at the right depth? –E.D., Hillsdale, MI

Answer: Recommended planting depths (as measured from the base of the bulb to the soil surface) are as follows for spring-flowering bulbs: two to three inches for crocuses, three to four inches for grape hyacinths (Muscari spp.) and Spanish bluebells (Hyacinthoides hispanica), five inches for Dutch irises, six inches for Dutch hyacinths, and eight inches for crown imperials (Fritillaria imperialis). Tulips and daffodils should also be planted eight inches deep, unless they are small bulbs, in which case five inches is sufficient. When in doubt about how deep to plant a particular bulb, follow the general rule of three times the height of the bulb.

It is OK to err on the side of planting too shallowly, because many bulbs possess contractile roots that serve to relocate the bulb to its ideal depth. This feature is what allows seedling bulbs to position themselves. Hyacinths, daffodils, lilies, some allium species, hymenocallis, and lycoris all have contractile roots. So do crocuses, freesias, gladioli, and triteleias, which all have corms rather than bulbs. Because new corms are produced on top of old ones, their roots must prevent succeeding generations of plants from rising out of the ground.

Tulips, however, lack contractile roots, so your question about how they reproduce from seeds is a good one. The answer is that after being exposed to low winter temperatures to satisfy their dormancy requirements, the tulip seed germinates. The seed leaf starts actively growing in the spring. The seedling produces a hollow, underground stemlike structure called a dropper. This grows downward and eventually produces a bulb at its tip, an inch or more below the surface. In suceeding years, new droppers yield bulbs deeper still.

I have a pond-lily cactus that blooms only every two or three years. The plant from which it came belonged to my mother 55 years ago. What can I do to make it bloom more often? –M.M., Franklin, CT

Answer: Your pond-lily cactus is one of the oldest known species of cultivated cacti. Native to southern Mexico, this rain forestdwelling epiphyte was called nopalxochitl by the Aztecs, from which its name Nopalxochia phyllanthoides was derived (although some authorities place it in the genus Disocactus). Its sawtooth stems reach 18 inches when grown in a hanging basket, and its rosy pink blooms resemble those of waterlilies.

Pond-lily cactus blooms from late winter to early summer. When grown indoors, give the plant bright but indirect light, and a soil mix of equal parts of peat, pine bark, and sand. To initiate flower bud formation, provide nighttime temperatures between 50 and 55°F with a daytime increase of 5 to 10 degrees. Keep the potting mix barely moist. Being potbound also encourages flowering.

When the flower buds are about an inch long, move your pond-lily cactus to a warmer location to enjoy its display.

When new stem growth begins in the spring, increase watering and begin fertilizing. Allow the top half-inch of soil to dry out before watering, and feed each month from May until October with a liquid, water-soluble fertilizer.

After the last frost, the plant can spend the summer outdoors in a shaded location. Cuttings root readily, but may take two to three years to reach flowering size.

I have a few new bonsai plants including a maple, beech, and peach. I believe that they need to be exposed to cold temperatures. How can I do that without injuring them? –R.C., Ada, OH

Answer: For the buds to emerge normally from rest, they must be exposed to a period of cold temperatures. This “chilling requirement” is expressed as a certain number of hours of exposure to temperatures between 32 and 45°F. The number of hours will vary with the species, and even the variety of plant. Lowchill peach varieties, for example, have been selected for warm climates.

When trees haven't been properly chilled, they won't leaf out properly, and their health will be compromised. To ready your trees for winter, leave them outdoors until after the first couple of frosts. Then move them to a location where the temperature will remain between 32 and 45°F. Provided that the temperature is kept low, the plants will not require light; they will only need to be checked periodically to be sure that the soil has not dried out. A cold cellar, unheated garage, or closed porch can provide the necessary conditions. Use a maximum-minimum thermometer to be sure that your plants are getting the appropriate temperatures. The risk of temperatures below freezing is damage to the roots. The above-ground parts of these plants tend to be considerably more cold hardy than the belowground ones.

When outdoor temperatures moderate, you can move your bonsai outdoors, although you will want to move the plants back inside if a hard freeze threatens.

Can you suggest a shadetolerant vine for the northfacing wall of my garage? This area receives absolutely no direct sunlight. –K.D., Pasadena, CA

Answer: What you choose to grow will depend in part on what sort of support you intend to provide. Some vines are clingers, attaching themselves directly to surfaces by means of aerial roots or other holdfasts. Others are twiners, which wrap around a support. For these, you will need to provide some sort of trellis, lattice, or at least ropes or wires for the vine to twine around.

Clinging vines include the evergreen creeping fig (Ficus pumila), tanglehead (Pileostegia viburnoides), climbing hydrangea (Hydrangea anomala subsp. petiolaris), and Japanese hydrangea vine (Schizophragma hydrangeoides). Aralia ivy (Fatshedera lizei) does not have holdfasts, but it is a shrubby vine that can be easily attached in an espalier form against a wall.

Twining vines you might consider include kangaroo vine (Cissus antarctica), star jasmine (Trachelospermum jasminoides), California Dutchman's pipe (Aristolochia californica), and the climbing lavender trumpet vine (Clytostoma callistegioides). Giant Burmese honeysuckle (Lonicera hildebrandiana), as its name implies, will need plenty of room, strong support for its twining stems, and attention to pruning to keep it in bounds.

Deciduous honeysuckles include a pair of natives—California honeysuckle (L. hispidula) and chaparral honeysuckle (L. interrupta)–as well as the shade-loving Chinese woodbine (L. tragophylla) and redgold honeysuckle (L. xtellmanniana).

Train newly planted twiners onto their vertical supports by securing one end of the string to the support and the other end to a stick driven next to the vine. As the vine grows, use soft twine or nylon to tie the vine to the support until it begins to twine or cling.

Can you give me information on so-called no-mow grasses? I have a cabin on Grand Manan Island in New Brunswick (USDA Zone 5a). No one is there to mow on a regular basis, yet I'd like to have grass over the leach field to anchor the soil. –M.S., New Brunswick, Canada

Answer: I'd recommend an assortment of fine fescues (Festuca spp.), which are adapted to dry, infertile, acidic soils (pH 5.5–6.5). These include creeping red fescue (Festuca rubra), chewing fescue (F. r. var. commutata), sheep fescue (F. ovina), and hard fescue (F. o. var. duriuscula).

Prairie Nursery in Westfield, Wisconsin (800–GRO–WILD;, offers the No Mow Low Maintenance Turf Mix, which is suited to any area in the Upper Midwest and northeastern United States, or to southern Canada, that gets at least 20 inches of annual rainfall. This fine fescue mix contains a blend of fescue varieties, some that spread by rhizomes or underground stems, and others that have a clump-forming or bunching nature. Although these grasses will tolerate shade, low fertility, and acid soil, they are intolerant of wet, poorly drained sites.

Despite the mixture's No Mow label, Neil Diboll, president of Prairie Nursery, recommends mowing the turf, at least to suppress the growth of invading shrubs and trees. For a wavy, natural look, mow once or twice per year—at a four-inch mower setting in mid-June to remove the seed heads that appear, and again, if you wish, in the fall. For a more managed look, mow monthly at a height of three to four inches. Leave your clippings on the lawn to recycle the nutrients. Newly sown seed will need to be watered, but once the lawn is established, no additional watering or fertilizer should be necessary. H

Pest Watch

Hemlock woolly adelgid (Adelges tsugae)

BIOLOGY: A native of Asia, the hemlock woolly adelgid first appeared on the West Coast in the 1920s, but has not become a problem there, in part because of the local native hemlock's natural resistance. The current epidemic in the East dates back to its secondary appearance in Richmond, Virginia, in 1951. Since then, the insect has spread west into the Smoky Mountains, south into the Carolinas, and north into New England, leaving a trail of dead hemlocks—both eastern hemlock (Tsuga canadensis) and Carolina hemlock (T. caroliniana). This pest is an all-female species, reproducing parthenogenetically (without fertilization). In early spring, adults lay from 50 to 300 eggs on hemlock twigs. When the nymphs hatch, they move to the base of needles where they settle down and begin to feed through their sucking mouthparts. Some develop into winged, migratory adults; others remain wingless, but can be spread by birds, squirrels, deer, and wind. A second generation of eggs is laid in early summer. The nymphs that hatch from these eggs remain dormant until fall, when they begin feeding.

SYMPTOMS: The first sign of infestation is usually a few young branches covered with white “wool” This is most noticeable in the early spring, about the time the ‘first eggs are laid. Where woolly adelgids have been feeding, the needles turn a grayish green color, then turn brown and de a result not only of the feeding, but of a toxin that the insects appear to be injecting. Trees can be attacked at any point from top to bottom, with dieback usually proceeding upward from the site of first damage. There is no immunity. Once infected, a hemlock tree usually dies within four years, regardless of its size or vigor.

CONTROL: All hemlocks should be inspected regularly. If woolly adelgids are discovered, the whole tree should be treated, because other branches may harbor less-visible populations. Annual treatments will be necessary indefinitely, a cost that must be taken into account in assessing the future value of the tree to a landscape.

Application of horticultural oil in early spring before new growth emerges, and again in the fall, will provide excellent control. Where the specimens are large, commercial arborists, with their mechanized spray equipment, may be needed to ensure adequate coverage of the tree.

Alternatively, you can apply imadacloprid (Bayer Advanced Garden Tree & Shrub Insect Control], a systemic insecticide, to the soil. Drench the soil of the root zone in the fall or spring, when the insecticide can be taken up and translocated in the sap. It's most effective on newly infested trees, because hemlock woolly adelgid feeding disrupts a tree's ability to take up water. One application can last for six months or longer.

Native predators have not proven to provide much control. However, a small black ladybird beetle (Pseudoscymnus tsugae) from Asia has been released in 11 eastern sites, in the hope that it will become a control. For now, the choices are either to spray annually, accept the loss of existing hemlocks, or plant resistant species. Resistant hemlocks include the Asian species-Chinese hemlock (T. chinensis), northern Japanese hemlock (T diversifolia), and southern Japanese hemlock (T sieboldii) and the West Coast natives—western hemlock (T. heterophylia) and mountain hemlock (T. mertensiana).