I know this has continued for more than a year because I threw salt onto the resulting ice last winter after one of the neighbors slipped on it. The "start time" changes with each occasional electrical outage so that irrigation now begins at approximately 11 a.m. What makes this problem serious is that the irrigation operates daily for an extensive duration—rain or shine!

Irrigation should be considerably less frequent during cool or damp weather, particularly during the winter, when days are shorter. Not only does the lawn or groundcover receiving irrigation consume less moisture during diminished vascular activity, but excessive moisture does not evaporate from the soil as readily. My lawn has actually not been irrigated since the first rain of autumn.

Species that exhibit shallow root systems require increased frequency of irrigation as weather becomes warmer but do not require excessive moisture. The duration of each irrigation cycle should only be sufficient to maintain adequate moisture until the next cycle. Superfluous moisture otherwise maintains saturation of lower strata. Although this is not necessarily detrimental to shallow roots, it can be very harmful to species that extend roots into deeper soil.

Species with more substantial and deep root systems, particularly most trees, prefer infrequent but generous irrigation. Although surface soil may become desiccated with such irrigation, moisture within lower soil should be optimal, without desiccation or saturation. Frequent irrigation necessary to maintain lawns is more easily tolerated by more substantial species if it is only enough to maintain moisture without saturation.

Symptoms associated with soil saturation are most obvious among trees. If roots cannot extend into deeper soil, they will disperse near the surface. Such roots may become exposed and distended, elevating pavement or other obstacles. Decay or root rot proliferates among roots that developed prior to saturation but have become inundated.

Friends of Guadalupe River Park & Gardens has scheduled a workshop with landscape architect Stephanie Morris, called "Water Wise Gardening," on Feb. 27 from 5 to 7 p.m. Irrigation, top-dressing, soil preparation and the selection of drought-tolerant species will be discussed. The workshop takes place at the Guadalupe Garden Center, located at 715 Spring St. in San Jose (just north of W. Taylor Street). Admission is $15 per person. Reservations may be arranged with Visa or MasterCard by telephoning 408.298.7657, by emailing education@grpg.org or by mailing a check or money order to Friends of Guadalupe River Park & Gardens, 50 W. San Fernando St., Suite 1100, San Jose, 95113.


Flower of the Week: Grevillea Noellii

I happen to be one of the very few people who are very allergic to Grevillea Noellii. Because the allergy is rare, some who are affected by it may be unaware of the origin. Symptoms resemble those caused by poison oak.

Some people know the species by its old common name, flowering pine, but it is more commonly known by the botanical name. With correct nomenclature, the genus name Grevillea is italicized because it is Latin. However, it lacks a species name that would also be italicized because it is believed to be a hybrid of unidentified parents. Noellii is not italicized because it designates a cultivar, not a species. That is more than you need to know but explains the inconsistency with typical species names that I am so critical about.

Grevillea Noellii tolerates more shade and irrigation than other grevilleas. The inch-long, slender leaves resemble pine needles. Small clusters of pink and white flowers that bloom for as much as two months in early spring are not profuse but are interesting. Mature specimens may be as high and wide as 4 feet.

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