Q&A with Bob Polomski 8

The orange blooms of my Clivia miniata have such short stems that they are almost lost in the foliage. What can I do to lengthen them?—D.G., Longwood, FL

Answer: Some Clivia clones produce longer flower stalks than others. But in general, the failure of the flower stalk, or peduncle, to elongate is the result of the plant's experiencing high temperatures during its rest period.

To initiate flower bud development, the plants should be exposed to a winter rest period at a temperature between 45° and 50°F. The soil should be kept nearly dry, yet never allowed to dry out completely. After six to eight weeks of this treatment, or once flower stalks appear, begin increasing the amount and frequency of watering. Move the plant to a warmer location, around 65°F during the day and between 50° and 55°F at night. Clivias require bright, indirect light, such as that from an east-facing window. To determine if light levels are adequate, put your hand about a foot above your clivia. If your hand creates a distinct shadow, the light is too bright and the plant needs to be moved to a lower-light location.

When the buds appear, fertilize with a complete liquid fertilizer on a monthly basis until the plant's winter rest. Remove the flower stalk soon after the flowers fade to prevent seed formation; this will encourage it to bloom next year.

For more information about the history and cultivation of clivias, see Clivias, by Harold Koopowitz (Timber Press, 2002).

I have inherited the care of several boxwoods that have been allowed to grow to a height of 40 inches. I would like to reduce their height to two feet, but if I cut off more than six inches I will reach bare wood. Any suggestions? —G.S., Travelers Rest, SC

Answer: With boxwoods, such drastic corrective pruning is possible, but it must be done over a period of years. Because boxwoods grow slowly, they recover slowly. Some may even die when severely pruned, so you will have to be careful.

The time to begin is just before new spring growth emerges. Prune one-third of the tallest branches to the desired height. Make your cuts to outer branches or buds. It is OK to cut back to bare wood. Boxwood, like most broadleaf evergreens, will produce growth from latent buds.

In the second spring, cut back half the remaining tall branches, and finish the job in the third spring. You may also decide to remove some of the oldest branches at the base to reduce the plant's width. Also, thin out some of the interior branches to admit sunlight and air, which will reduce the likelihood of fungal diseases.

Which is the best season to transplant deciduous trees, spring or fall?—M.H., Plainfield, IL

Answer: Trees have survived transplanting in every season. The question, though, is which time of year is best. Digging up any tree results in the loss of a great deal of the root system. Whether the tree is balled-and-burlapped or moved bareroot, only a small fraction of the original root system makes the move. The ideal time to move a tree, therefore, should allow the tree an opportunity to begin root regeneration as soon as possible. The best time, then, depends on where you live and with which species you are dealing.

In the northern United States, transplanting has traditionally been delayed until spring, in the conviction that this allows the tree as much time as possible to regenerate roots before the ground freezes solid. In addition, certain species, such as oaks, will not initiate root growth until buds swell in the spring. Northern red oak, in fact, begins root growth only after spring bud break. The new leaves and shoots create an additional demand for water, making transplanting the trees even more difficult. Some trees, such as elms, hollies, and magnolias, on the other hand, have flushes of root growth in midsummer, and have been successfully balled-and-burlapped even in full leaf. In such cases, survival depends on the availability of water.

Despite the traditional preference for spring planting, recent research has demonstrated that many trees may be better transplanted in the fall. In one study, October-transplanted sugar maples did better than November- or March-transplanted trees. The sugar maples produced roots sporadically throughout the winter months. Even in the case of red oaks, the results were similar. The red oaks did not begin root growth until after bud break in the spring, but the days between bud break and root growth were fewer for the October-planted than the March-planted specimens.

Before we conclude that fall planting is universally superior, it should be noted that this research was done in Blacksburg, Virginia, where fall is longer and winters not as severe as in more northern locales. When trees are to be transplanted in the fall, do it at least four weeks before soil temperatures drop below 40°F.

Other factors besides timing also affect how well a tree survives transplanting. These include the tree's health prior to the move, the size of the root ball, whether the roots are kept moist in transit, and the care the tree receives after transplanting. The greatest hindrance to transplanting success is a lack of water in the plant's tissues. This water stress, known as “transplant shock,” occurs because of the tree's inability to absorb moisture because of its reduced root system.

Whenever you transplant, water your tree regularly to support the growth of roots in its new location. Depending on the weather and rainfall, water daily for the first few weeks. After that, cut back on watering to every few days, or longer, especially during cloudy, rainy, or cool weather. Eventually, water on a weekly or “as needed” basis, testing the soil and root ball for moisture.

My seedling apricot tree is 15 years old. It blossoms every year, but any fruit falls off a month after it begins to develop. Why?—E.L., Sunnyvale, CA

Answer: The best apricot production occurs in regions that experience dry spring weather. Cold, rainy, windy conditions between February and March, when apricots are blooming, will hamper pollination and subsequent fertilization of the flowers. Late spring frosts will also take their toll on the developing fruits. Warm temperatures are necessary for at least three weeks after full bloom to ensure good bee activity and the completion of pollen tube growth, fertilization, and early fruit development.

It is also possible that your seedling is self-incompatible. While some apricot varieties are self-fertile, many are more fruitful when cross-pollinated, and some varieties require that there be another compatible variety planted nearby.

Even under the best of conditions, some loss of developing fruit is to be expected. A high percentage of apricot flowers do not lead to mature fruits. So-called June drop, where the immature fruits are shed, should not, however, result in a crop loss.

Pam Peirce, author of Golden Gate Gardening (Sasquatch, 1998), recommends the following apricot varieties for your region: ‘Royal’ (’Blenheim’), ‘Goldkist’, ‘Flora Gold’, and ‘Katy’.

I brought my bougainvillea indoors for the winter and it's shedding its leaves. What do I need to do to help it make it through the winter?—L.L., Brentwood, TN

Answer: This tropical vining shrub is an evergreen in its native Brazil, Colombia, and Peru, but here, leaf shedding can be expected during the winter months. Keep your bougainvillea in a cool environment and allow the soil to dry out between waterings.

In the spring, trim away weak, spindly growth and cut back any long thorny shoots to short spurs with two or three buds. Keeping the plant potbound will encourage flowering, which should occur in late winter through the summer. Before taking your bougainvillea outside (after any danger of frost has passed), gradually expose it to increasing levels of light. Eventually move it to a full-sun location.

During the growing season, fertilize monthly with a balanced liquid water-soluble fertilizer. Pinch new growth back occasionally to keep the plant bushy and attractive. Keeping the shoots to one-and-a-half or two feet long will improve the floral display.

I found a variegated climbing vine at a local garden sale. It's called porcelain berry and has lacy leaves. Can you tell me anything about it?—E.B., by e-mail

Answer: Porcelain berry (Ampelopsis glandulosa var. brevipedunculata) is native to China, Japan, and Korea; the cultivar ‘Elegans’ is a variegated selection.

Although it is admired for its clusters of shiny blue to purple fruit in autumn, this vine has escaped from cultivation in states from southern New England to North Carolina and west to Michigan. The bird-dispersed fruits have given rise to thickets of vines at the edges of woodlands. These imperil native plants.

The vine, once established, will grow to 20 feet and is hard to eradicate. Repeated cutting or pulling, shading out, and/or the application of glyphosate herbicide in early autumn are less desirable alternatives to not planting the vine in the first place. H

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