July 17, 2002      Sunnyvale, California  Since 1994



Garden

Photograph by Shari Kaplan Often considered a weed, the cattail actually has many uses. Its sap is a mild antiseptic and anesthetic, its young shoots are edible, and its leaves can be woven into baskets. Many plants, trees can be damaged by heat and sun By Tony Tomeo Air conditioning would be nice. It gets so warm in my home that candles melt and hang upside down if not refrigerated during warm weather. The lobelia that I wrote about unseasonably early is now quite crispy. It actually is a summer annual, but not much can tolerate the heat and reflected glare where the lobelia is located. Just as many species that are sensitive to cold need protection from frost, many species require protection from harsh climactic conditions associated with heat. Heat alone is a problem only among sensitive species or if heat is extreme. It is much more damaging in conjunction with minimal humidity and excessive exposure to sunlight. Many of the species that are more sensitive to heat and associated climactic conditions are "understory" species. Such species in the wild inhabit the forest floor or areas below larger species. Fuchsias, rhododendrons, begonias and various ferns are some of the more familiar understory species. Not only are understory species normally protected from direct sun exposure, they also do not extend their roots as deeply as more exposed species. Species that are normally exposed exhibit deeper roots that can reach moisture in lower soil strata to compensate for moisture lost to evapotranspiration (evaporation from foliar surfaces). Because forest floors are typically humid and sheltered from dehydrating breezes, evapotranspiration is somewhat inhibited. Deep roots are consequently not necessary. Foliage of understory species is designed to maximize foliar area but lacks the thick cuticles exhibited by species that must conserve foliar moisture. Delicate and thin foliage becomes desiccated much more readily. Of course, even the toughest of species can be scorched or scalded if heat and low humidity are enhanced by reflected glare. (Foliage is scorched; stems are scalded.) Pavement, walls, windows, roofs and even parked cars are all reflective surfaces. However, scorch and scald among tougher species are rare where foliar density sufficiently shades reflective surfaces. Because bare soil is somewhat reflective and certainly does not absorb glare, small, newly installed plants are more sensitive to heat damage until they grow large enough to provide enough shade for themselves. Parts of the plants that were shaded in crowded nursery conditions are the most sensitive. Coarse mulch absorbs glare better than bare soil and also increases humidity if moisture is maintained. Even where regular irrigation is not practical, such as near established oak trees, periodic light rinsing with water during the warmest weather adds considerable humidity to the air. Scald is not primarily limited to understory species, but can damage excessively exposed stems of many species. The most severe scald occurs on stems that have matured in shade and have suddenly become exposed. In fact, one of the largest silver maples I have inspected was completely destroyed by scald that resulted from severe pruning that removed too much of the foliar canopy. Maples, English walnuts, citrus, figs, ash and species that exhibit smooth bark are typically more sensitive. However, even the shaggiest of coast redwood trees can be damaged in severe situations. Plant of the Week: Cattail Cottage pink, Dianthus plumarius, and the less common maiden pink, Dianthus deltoides, are both classic perennials that have been enjoyed in gardens for several centuries and have been used to breed the many more contemporary varieties that are now available. I would agree with many who are familiar with cattail, Typha latifolia, that it is a weed. Cattail spreads through swampy areas by creeping stolons. The profuse seed can be transmitted to other areas that have not yet been infested. This would be obvious to anyone who attended the open house at Bay Laurel Nursery and noticed how the marsh looked! They're all over the place! Although cattails can be a problem if not contained, they are striking in smaller garden water features. Unfortunately, they are not readily available and must be obtained either from nurseries that provide aquatic species or from a neighbor's marsh. If transplanted, foliage quickly turns brown and abscises, but new growth should appear in spring. The one-inch-wide, vertical foliage can be as tall as eight feet. The familiar dark brown female flowers resemble cats' tails or corn dogs. The slender parts above contain the male flowers. The wide "corn dog" part is what explodes into fluffy white seeds. The less common Typha angustifolia exhibits narrower and taller foliage, lighter brown corn dogs and a small stretch of bare stem between the male and female flowers. Horticulturist Tony Tomeo can be contacted at 408-358-2574 or at LGHORTICULTURE@aol.com.

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