Buying Into the Ivy League

By Scott Aker
Special to The Washington Post
Thursday, July 5, 2007

Q Can you give me a source for buying 50 young Boston ivy plants?

ABoston ivy is the Asian counterpart of our native Virginia creeper, and famous as the wall-clinging vine that gives the Ivy League universities their nickname. It has very glossy, deep green leaves with three lobes that turn bright red in fall. It clasps to surfaces to support itself with modified leaves that are known as holdfasts. On Boston ivy, these are crescent-shaped, while they are round on Virginia creeper. This feature can be used to identify the vines even when devoid of leaves.

Boston ivy is not as commonly grown as it once was; perhaps it has fallen from favor because of the holdfasts, which are thought to deteriorate the wood, stucco and concrete that they climb on. Plan to keep it off door and window frames, and certainly keep it off window screens. In our climate, it is sometimes afflicted with fungal leaf spot, which may cause it to defoliate in some years.

In the quantity that you are looking for, I would urge you to look for rooted cuttings. Classy Groundcovers might be a good source for large quantities of small plants ( A spokeswoman said cuttings will be available around Oct. 1 for fall planting.

We have a 30-year-old white pine that seems to be suffering from construction activity during the building of an addition that predates us. At the very least a third of the root system was covered by one to two feet of soil that cannot be removed, although the tree trunk itself is not covered with soil. We have been told that treating it with something called Cambistat may promote increased root development. Would you agree?

Cambistat is an arborist formulation of a plant growth regulator used in the greenhouse industry to keep potted florist crops such as Easter lily short and stocky. It slows growth and causes leaves to be smaller, thicker and deeper green. It may cause enhanced growth of fibrous roots, which is probably why it was recommended to you as a treatment for your ailing white pine.

Anytime a tree's roots are injured, the impact may take several years to manifest itself. Typically, at least two years must pass before the full effect of the injury results in stunted growth of branches or dieback. Often, five years may pass before the full impact of the injury is apparent in the tree's branches.

If your pine has lost a significant portion of its anchoring roots on one side, the tree may have an increased chance of suffering windthrow. White pines are particularly susceptible to storm damage in our climate because the soft needles hold on to slushy snow and ice in a way that pines with stiffer needles do not. Add a bit of wind, and you may have a real disaster on your hands. If the tree is far from structures that it could harm, there is little to be concerned about. Your tree sounds as if it is close to a recent addition to your home, so you may want to have an arborist evaluate it to determine if it presents a hazard. On the plus side, it seems that the grade was not changed near the trunk of the tree, so the main anchoring roots may have been preserved.

The Cambistat could cause the roots to grow more fibrous, and that will help the tree recover. This is a sort of side effect of the plant growth regulator, which has been touted as a means to keep trees under power lines from growing too rapidly into the overhead lines. It has also been marketed as a means to keep trees looking good in marginal environments such as those found along urban streets and in poor, dry soils. While there is some evidence that they work, it is a treatment that must be reapplied regularly to maintain the desired results.

Don't expect the Cambistat to be a silver bullet, though. If the extent of the damage was over the threshold that the tree can ultimately tolerate, it may still decline, and even die. Try to keep other stresses to a minimum. Don't compact the soil anywhere near the tree, and don't irrigate the root zone too frequently. Avoid the temptation to apply fertilizer. It will not really promote root growth that can be sustained and may cause pine bark aphids to propagate wildly on the tree, hastening its demise. Allow the needles to lie under the tree as a natural mulch.

Scott Aker is a horticulturist at the U.S. National Arboretum.

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