English ivy (Hedera helix) can provide warmth and protection to a brick building without being a hazard, according to Dr. Henry T. Skinner, former director, U.S. National Arboretum. It is not a parasite and does not strangle trees, Dr. Skinner says.
Henri K. E. Schaepman, president of the American by Society, says he agrees with Dr. Skinner.
Dr. Skinner took exception to a statement by Suzanne W. Pierot, past president of the American Ivy Society, in her book, "The Ivy Book," (Macmillan - $4.59) which also in answer to a garden question. The statement follows:
"Of course ivy does loosen mortar (between the bricks of a building). It does get under clapboards. It can be destructive and must be kept in check on some buildings. All you need is the money for repairs."
"It is certainly true," Dr. Skinner says, "by sheer pressure of vegetative growth ivy can pry loose ill fitting clapboards, gutters and the like if permitted to do so. But I would very much like to know what evidence has led Mrs. Pierot to the belief that "Of course ivy does loosen mortar."
"Ivy climbs by means of root-like holdfasts which attach themselves to any moderately porous surface, whether brick, bark, or mortar, but these are not true roots and in my opinion they do not cause damage through penetration beyond the portous surface so long as the mortar itself is of good quality and remains intact.
"Bricks laid with poor quality mortar will need periodic repointing whether ivy covered or not. They may need this more frequently, in all probability if lacking the weather protection, which ivy affords.
"Our brick -on-stone cottage purchased a few years ago (by Dr. and Mrs. Skinner) in Kent, England, is pleasant enough to look at but suffers from soft bricks and soft mortar, being a product of obvious jerry building of the early 19th century. It has never been vine-covered, yet its original mortar persistently weathers to leave deepening gaps between the bricks.
In September (1976), we let a contract for repointing, the second in six years.
"Within a quarter of a mile stands a much older timbered and brick home whose all-brick west front has been ivy covered completely for at least 90 years.
"The ivy has always been cut back tightly and top-trimmed each spring. No pointing has been undertaken in recent memory, nor is any currently needed. The original mortar was doubtless of better quality than that of our cottage whose weathering problems could conceivably be reduced by provision of an ivy cover.
"It is interesting that Johnson's (English) Cottage Gardener's Dictionary of the last century commends ivy for its provision of warmth, protection and dryness to buildings. Johnson makes no allusion to deleterious effects, yet he was a good observer and was presumably honest.
"The fact that ivy is not a parasite is scarcely the reason why it is a nonstrangler of trees. It fails to strangle only because it is a non-twining vine unlike, for instance, wisteria.
"Ivy can damage a tree but only, apparently, when permitted to so invade the crown that functioning of the tree's leaft canopy is impaired by shading, or that is bulk and density renders the tree critically suscpetible to wind breakage."
Skinner became director of the National Arboretum in 1952, succeeding B.Y. Morrison, who retired. Skinner retired in January 1973 and was succeeded by Dr. John L. Creech.
Skinner is past president of the American Association of Botanical Gardens and Arboreta, past president of the American Horticultural Society, and has served as a member of the executive committee of the International Society for Horticultural Science.
He has received many awards, including the Liberty Hyde Bailey Medal for 1972 of the American Horticultural Society, considered the highest honor that is given in the field of American horticulture.
The award went to Skinner for his role in building the National Arboretum into a place of national and international prominence in the plant world.