Native species have been increasingly displaced from urban areas by exotic (nonnative) species during the previous two centuries or so, but the natives still persist and are still popular among many garden enthusiasts. The California Native Plant Society's Spring Native Plant Sale is an excellent source of many plants, seed and bulbs of native species.

The sale runs from 10 a.m. to 4 p.m. on May 8 at the California Native Plant Society Nursery at Hidden Villa Ranch, located at 26870 Moody Road in Los Altos Hills. Parking is limited so carpooling is recommended. More information may be obtained by telephoning 650.941.1068 or online at cnps-scv.org.

It would seem that because the local climate is so mild, native species would not need to have developed any special adaptations. Such adaptations would seem more necessary where weather can become severely cold during winter or hot during summer. Local climate does neither, but can be quite arid at times. This is why several native species have developed the capacity for variable dormancy.

For example, California horse chestnut and California sycamore may emerge from dormancy during spring, but may partially defoliate if weather becomes unseasonably warm and dry during summer or even spring. If this happens, they can "refoliate" as weather allows, but prior to cool winter weather that stimulates complete dormancy. Sycamores can also behave like this in response to fungal infection, as was so common last spring as anthracnose proliferated during alternating warm and rainy weather.

Spring seems to have arrived early this year, and weather has recently been warmer than it has been for this time of year since 1965. If this weather pattern continues, foliage may subsequently become dingy among sycamore, London plane (a hybrid of Japanese sycamore and California sycamore) and even valley oak. Sycamores that are not within irrigated areas or near an active creek may eventually begin to partially defoliate.

Just as some species are sensitive to frost during winter, a few species are sensitive to unseasonable warmth while foliage is only beginning to emerge from dormancy. Foliage typically matures and becomes more resilient as weather slowly warms from spring to summer. However, if weather becomes too warm too rapidly, tender new foliage may be damaged by direct exposure to sunlight, particularly if humidity is minimal or a breeze enhances evapotranspiration.

Tree of the Week: New Zealand tea tree

"Limeys" were not citrus farmers, but English sailors who used limes to prevent scurvy. Captain Cook's crew members either depleted their supply of limes or just wanted to try something new, so they brewed tea from the foliage of the New Zealand tea tree, Leptospermum scoparium, as an alternative scurvy prevention.

Each of the various cultivars exhibits distinctive characteristics, but the "straight species" is not common. The largest of the cultivars are about 10 feet tall when mature, and others are very low or even sprawling. Bloom appears mostly between spring and summer, and floral color ranges from deep red to pink to white. Flowers are either single or double but are less than a half-inch wide. The dense foliage is usually brownish green, but some cultivars exhibit dark reddish foliage. Individual leaves are small and narrow, mostly less than a half-inch long.

New specimens will require regular irrigation until roots are dispersed, but established specimens need only minimal irrigation, if any at all. If irrigated, soil must drain well because New Zealand tea tree is sensitive to root rot. Full sun exposure is preferred. Occasional light shearing is tolerable but compromises the appealing natural form of New Zealand tea tree.

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