This is, ironically, the weather pattern that promotes production of maple sugar. Warm weather stimulates vascular activity (flow of sap), but frost during the night maintains the trees' dormancy, prolonging the process. Maple sugar is not produced here because winter is too mild and brief to initiate prolonged dormancy and spring typically begins so abruptly, without night frosts.

I still intend to obtain at least a small volume of maple syrup from my eight sugar maple trees when they are older so that I can brag about it to all of my colleagues who insist that it cannot be done. I have actually obtained a very small amount during a very brief time (I think in 1999) from the native big leaf maple (or Pacific coast maple), but after evaporation, it tasted like very sweet instant coffee with grass and olives, or something like that. The trees are at a nursery in the Santa Cruz Mountains, where winters are cooler, but my colleagues do not need to know that.

Because of the unseasonably warm weather, most grafting of deciduous species must be completed soon, like winter pruning, prior to bloom and resumption of vascular activity. If grafted too late, cambium layers will be unable to knit, and the scion (the stem that is grafted to rootstock) will become desiccated.

James Kern, master gardener and member of the California Rare Fruit Tree Growers association, will be giving a lecture titled "Grafting Fruit Trees" at Common Ground Garden Supply and Education Center from 10:30 a.m. to noon on Feb. 22. Admission is $17, and reservations can be arranged at Common Ground at 559 College Ave. in Palo Alto, by calling 650.493.6072 or by visiting www.commongroundinpaloalto.org.


Tree of the week: Japanese black pine

I recently met a specimen of dwarf Japanese black pine while delivering a rhododendron to a residential garden. I had never seen one before, and I am told that it is quite rare. I am now very interested in how this particular tree matures and how it resembles the "normal" Japanese black pine, Pinus thunbergiana. Although the owner, Mr. Zigerelli, had difficulty obtaining this rare (and expensive) dwarf cultivar, Japanese black pine is one of the more commonly available pines.

Pines generally require full sun exposure and prefer soil that drains well. Dense soil that does not drain well is tolerable if irrigation is not excessive. Saturation of soil easily damages mature roots and inhibits dispersion of roots into lower soil strata. Fertilizer should not be necessary and may actually promote distended but sparsely foliated growth. Pines are susceptible to several pathogens if stressed but are considerably less susceptible when healthy. The foliage can be damaged by substantial aerial toxins, such as smog.

In the Santa Clara Valley, Japanese black pine typically grows somewhat slowly to approximately 15 or 20 feet, but it can grow rapidly to 100 feet in coastal areas of Oregon and Washington. It is more easily shaped by pruning than other pines are. The natural form is broadly conical when young, becoming broader and more irregularly structured with maturity. Some specimens develop irregularity of structure very early, without ever exhibiting the more typical conical form. The pairs of stiff, bright green needles are approximately 3 or 4 inches long. The 3-inch-long cones are also bright green and become a cinnamon brown color as they open. Emerging new growth with juvenile needles, known as "candles," may be pruned to control growth or enhance foliar density.

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