Privet, the wire-haired terrier, is more efficient with his personal temperature regulation by defoliating his inner furry winter coat as weather becomes warm. The remaining wiry hair provides shade, but is not as obstructive to cooling air circulation as the winter coat is. Regardless of defoliation, his coat is more substantial than my beard and I still do not understand how it can be at all comfortable during summer.

Even during the warmest days of summer, heat alone only damages a few sensitive plant species. Extreme solar exposure, minimal humidity or insufficient soil moisture causes what some call "heat damage." Increased vascular activity during warm weather enhances sensitivity to such damage. Sun scald and foliar burn are the most common heat damage, but roots within containers may indirectly become damaged by solar exposure.

Most species that may be damaged by cambial sun scald of trunks and limbs are typically sufficiently foliated by mid summer to provide protective shade to sensitive parts. However, trunks of trees that have been improperly pruned or trees with narrow canopies lacking lower limbs may be detrimentally exposed. Such exposure is enhanced by reflective glare from pavement, walls, large windows and even parked cars and that once popular white "moonrock." Of course, some species are more sensitive than others. For example, various species and cultivars of maple, cherry and apple are very sensitive, but pine, cypress and cedar are considerably more resilient.

Trunks of the orchard trees throughout the Santa Clara Valley were painted white for protection from solar exposure until foliar canopies could provide sufficient shade and bark had become striated. This is unfortunately unsightly in a garden. Although stakes in direct proximity to the trunks of young trees should not be necessary for support and may actually inhibit development of caliper (more on that topic later), they may provide protection from scald if tied loosely to the south side of the trunk. Such stakes need not be large, but can be very effective if they break up the exposure during midday. Duct tape applied vertically to the trunk (not wrapped around it!) is also effective.

Roots may be "cooked" within inadequately insulated containers that are too exposed. Black vinyl cans used for nursery production are useful for their intended function, but become very warm if exposed to the sun and transfer the heat directly to contained media and roots. Heavier clay pots and wooden planter boxes are much better insulated and more appropriate for exposed areas. Of course, any container may be used for specimens that are large enough to shade their roots or if the container is contained within a larger container.


Species of the Week: Hen and Chicks

I really do not know what species of hen and chicks (or "chix"), Echeveria spp., we photographed at the 2003 San Francisco Flower & Garden Show. Although not every species is commonly available, several are. The names and identification of these can be somewhat confusing for a novice. All exhibit rosettes of succulent grayish or bluish green foliage, and most produce pups that are known as chix because hens do not ... well, you can figure it out. Individual leaves are wide and blunt, but some plants produce narrower, pointed or thicker leaves that resemble those of aloe.

Some contemporary varieties are blushed with red, burgundy or bronze. Thin, arching stems suspend small and pendulous red, pink or yellow flowers that seem to be too delicate to have originated from such bold foliage. Hen and chix, like many echeverias, is somewhat drought tolerant, but is also happy with regular irrigation, if drainage is adequate.

Horticulturist Tony Tomeo can be contacted at 408-358-2574 or at LGHORTICULTURE@aol.com.