In those reports, with very few exceptions, the inspections of commercial sites that I conduct invariably include the equivalent of "Irrigation is too frequent to adequately drain from the endemic dense soil. Consistent saturation of soil has inhibited development of a healthy root system."

Unfortunately, the various species within most landscapes require specific but different duration and frequency of irrigation. Lawns and most annuals only extend roots into the upper few inches of soil. Consequently, frequent but not necessarily generous irrigation is necessary to prevent desiccation of the surface soil and the roots contained within it. However, most trees and other, more substantial species prefer less frequent but generous irrigation that will penetrate to the lower level of soil without maintaining saturation.

If irrigation is both frequent and generous, surface soil may sustain lawns and annual species, but the lower level of soil is more likely to be too saturated for roots of larger species. I occasionally inspect areas that are so saturated that even annuals or lawn grass cannot survive! The most effective solution to the problem is obviously adjustment of irrigation.

Trees and shrubs require frequent irrigation when initially installed because roots are confined to such a small volume of soil. Some garden enthusiasts prefer to install watering tubes, which are merely empty vertical pipes that extend to approximately 18 inches below the surface of the soil. Infrequent but generous irrigation applied directly into these pipes may promote development of deeper root systems, but only if surface irrigation is minimal and soil is not consistently saturated.

Organic soil amendments temporarily improve drainage during the time that new specimens are becoming established. By the time the amendments decompose, the new specimens should have become established and no longer require enhanced drainage.

Another free workshop, "Composting: the Simple Solution to So Many Problems," is scheduled for 6 to 8 p.m. on Oct. 17 at the Guadalupe Garden Center. Master composter Phil Cornish will discuss many aspects of composting, including what can be composted, what can be done with finished compost, methods of composting and tools necessary for composting. Attendance is limited, so reservations should be made with the education coordinator by calling 408.298.7657 or emailing info@grpg.org. More information is available at www.grpg.org. The Guadalupe Garden Center is located at 715 Spring St. at Taylor in San Jose.


Perennial of the Week: Mother-in-law's tongue

Mother-in-law's tongue, Sansevieria trifasciata, which is also known as snake plant, is one of the most resilient houseplants, easily tolerating variations of temperatures, solar exposure and irrigation, as well as minimal humidity, which is typical of home environments. Bright ambient solar exposure is preferred, but considerable shade is tolerated. Direct solar exposure or reflective glare may cause foliar scorch or foliar discoloration that resembles chlorosis. Irrigation should not be so frequent that the soil or potting media is consistently saturated. Infrequent but thorough irrigation is preferred to excessive irrigation, but desiccation will inhibit growth.

Small plants can grow disproportionately large while confined to small containers. Mother-in-law's tongue may be grown in the garden if protected from frost and snails. The thick, succulent leaves are rigidly vertical up to 4 feet tall and 2¹/2 inches wide, originating from tough horizontal rhizomes. Foliage is dark green with distinctively striped gray "chevrons" centered on the midribs. Each of the few cultivars exhibit distinctive variegation or stripes. Delicate white floral clusters are fragrant but rare.

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