Mike McCullough, a charter member of the De Anza chapter of the American Rhododendron Society, will conduct a similar workshop at noon on Sept. 14 at 161 Sausal Drive in Portola Valley. Guests can bring a bag lunch and meet with members of the society for lunch at 11:30 a.m. Material and cuttings from various rhododendrons, including cultivars of Rhododendron maddenii, will be provided. More information is available online at www.deanza-ars.com.

There is a prevalent misconception that rhododendrons are difficult to grow successfully. However, they perform well even in the Santa Clara Valley with less attention than more commonly grown roses if their cultural and environmental requirements are fulfilled. The cultural requirements are somewhat specialized and seasonal, but not extensive. Like roses, rhododendrons appreciate seasonal fertilizer and deadheading after bloom.

Selection of rhododendrons conducive to endemic environmental conditions is simpler than modification of environmental conditions to appease a particular cultivar. Many cultivars have been developed for warmer and arid climates and may perform as well here as the classic cultivars perform in the Northwest.

Rhododendrons that have been grown locally adapt more easily to their new garden environment because the climate is not as unfamiliar as it is to rhododendrons grown in other climates. Rhododendrons from the Northwest may need to adapt to warm and dry air as well as alkaline soil and water. Many of the cultivars that prefer other climates are unable to adapt completely.

Rhododendrons require several years of growth to be marketable. "Factory grown" specimens that have been rushed to grow at the same rate as other crops are of inferior quality, with minimal root development. The best specimens are grown by local establishments that specialize in rhododendrons. Wholesale nurseries or growers are not open for retail sales, but their products are available at local retail establishments.

Soil in the Santa Clara Valley and much of the Santa Cruz Mountains is dense and does not drain sufficiently for shallow rhododendron roots. Irrigation should be as frequent for rhododendrons as for lawns. However, if irrigation is both frequent and too generous, slowly drained soil remains saturated, so established roots rot and new roots are unable to disperse. Drainage should be enhanced with soil amendments such as shredded redwood conditioner.


Plant of the Week: Dumb cane

One of my colleagues at Cal Poly, San Luis Obispo who doubted that dumb cane, Dieffenbachia amoena, could paralyze vocal cords tasted some and was consequently hospitalized for the extraction of the dangerously sharp crystals that formed when the sap reacted with saliva. Dumb cane certainly should not be within reach of anyone who might chew it. The soft, broad leaves range in color from dark green to light yellow-green and may be as long as 8 inches. Each cultivar exhibits distinctive spotted, blotched, veined or striped variegations of white, pale white or light yellow.

Dumb cane are typically grown in containers as houseplants but may be relocated to sheltered locations outside, such as porches, from spring to autumn. Bright ambient light is preferred, as direct exposure to sunlight can cause foliar burn. Rotation of the pot will inhibit the tendency of new growth to lean toward light. Soil should be rich and drain very well. Irrigation should only be applied when the surface of the soil appears dry.

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