If, as seems likely, this very warm spring becomes a very warm summer, it's a safe bet that people east of the hills will spend a fair amount of time in the coolest parts of their yards. And if that intense summer heat raises a huge wall of thick fog from the ocean and dashes it up against the east shore of the Bay, as seems likely, then people in Albany and the Richmond Annex will tend to congregate in protected, south-facing spaces.
That should come as no big news to anyone who has heard the bad old joke about Highway 24 going through the "Cold-to-Hot Tunnel." If you commute from Walnut Creek into San Francisco in September, you probably grab a jacket to put on at the Embarcadero. For people living in the East Bay, or anywhere along the corrugated landscapes of the West Coast for that matter, microclimates are a fact of life so basic that we tend not to notice them until they make us really uncomfortable.
But we humans are lucky. When our immediate microclimates make us uncomfortable, we can get up, move around, or change into skimpy clothes. The plants in our gardens have somewhat more limited options. They can die. They can struggle, maybe adapting to a less-than-ideal situation by putting out substandard leaves, flowers, or fruit. Or they can luck out by finding a caretaker who pays a bit of attention to local conditions, and changes those conditions or selects plants accordingly, or both.
Our local landscape would look very different if it weren't for microclimates. That great big redwood forest atop the Oakland hills wouldn't exist if those hills weren't licked by tongues of fog snaking through the Golden Gate. Ride your mountain bike along the Skyline Trail in the summer, and look at the side canyons. Notice a difference between the north- and south-facing slopes? The north-facing ones are often covered in lush oak and bay laurel. South-facing slopes, blasted by the direct sun, bear sere coats of dried grasses dotted with droughty poison oak and coyote brush.
Even on the smaller scale of your yard, the relative position of the sun is crucial; it's one of the first things beginning gardeners learn. There are sun plants and there are shade plants, and woe to the gardener who plants a tender fern on a sunny, south-facing slope, or a tomato on the north side of the house under an oak tree.
It's not just exposure to the sun that determines your microclimate: a host of other factors determine whether your yard is better suited to growing cacti or moss. Proximity to large bodies of water is a big one. The Pacific Ocean -- with its minor partner, the Bay -- acts as a kind of thermal flywheel, cooling the nearby land when it's hot out, and keeping it relatively warm at night or during the winter. From San Lorenzo to Martinez, East Bay communities with close-up Bay frontage tend not to have big differences between the day's high and low temperatures.
Further from the really big water -- say, in Antioch, where the Delta begins, or in landlocked Livermore -- the marine influence lessens. Summers get hotter, and winter freezes are harder and more frequent. Block the flow of air off the bay -- with a two-thousand-foot range of hills, for instance -- and the distance needed to create truly warm summers diminishes. This is why Orinda's climate more closely resembles San Ramon's than it does Berkeley's.
And then there's fog, which accentuates and complicates the whole marine influence. If prevailing winds or topography tend to carry the fog over your yard from the ocean, you can enjoy temperatures a dozen or more degrees lower than your friends in nearby neighborhoods. I spent four years living in the Richmond flats, in a neighborhood that was foggy when the sun shone everywhere else in the East Bay. Neighbors five blocks away had too many tomatoes to eat in July, but none of mine ripened before the end of August.
This is probably the aspect of our local microclimates that most confuses gardeners who've moved from more uniform climes, like England or New Jersey. Most other places, sun is sun and shade is shade. But "full sun" in a foggy bayside town may be just fine for a traditional shade plant like impatiens, while six hours of sun in Livermore might roast a chile pepper.
Even without fog riding on it, a good stiff prevailing wind, like you might find in passes atop the hills, is an effective air conditioner for your yard. This is a good thing in summer when you're trying to keep thirsty garden plants alive: Lower temperatures mean plants need less water. But during the winter, when the mercury hovers just above freezing for long nights, the extra cold from a steady wind can mean a chilly end for your tender subtropical plants.
Since that wouldn't be complicated enough on its own, it turns out that a spot on a hill can also make a garden a bit warmer. As you may remember from high-school physics, hot air rises. As it does so, any nearby cold air flows downhill to take its place. If your garden is on the side of a hill, it may be a few degrees warmer than the yards of your flatland neighbors, as your cold air flows downhill to kill their pepper plants. This is largely the reason that some East Bay neighborhoods, Temescal and Laurel among them, are so-called banana belts, significantly warmer than their surroundings. You can generally tell when you're in a banana belt, even though the land's elevation may be too subtle to notice. For one thing, bananas do grow really well in such neighborhoods, forming thick, healthy clumps rather than the sickly, spindly waifs you might see in chillier 'hoods. Bird-of-paradise flowers bloom profusely in banana belts, and other subtropical landscape plants -- like princess flowers, tree ferns, or philodendrons -- just look happier.
The banana-belt phenomenon is writ large, of course, in the Berkeley and Oakland hills. East of the Hayward Fault, cold air drains toward the bay so efficiently that some parts of the hills' western slope rarely see a hard frost. Gardeners in these hills are truly blessed with moderately warm summers and winters that don't get too cold. Many plants sold as annuals in the rest of the world will live for years in the hills, truly one of the best horticultural climates the world has to offer.
But if you're not lucky enough to live above Route 13, you can still take advantage of microclimates -- or create some of your own -- to help your garden thrive. The key is paying attention to how your garden works. Does the fog linger late into the afternoon? Try planting sun-greedy plants against a south-facing wall to soak up all the heat that's available, and paint that wall white to maximize the light. Are you in a low spot that frosts over when the rest of the Bay Area is still in barbecue season? Consider planting things that appreciate the cold, like apples, peonies, or lilacs, and stick those cymbidium orchids under a roof to keep their heat from radiating directly into the cosmos. Got a steep, south-facing hill with a Bay view? Look into drought-tolerant plants, so that the warmth (and difficulty in watering without runoff) can work to your advantage.
Above all, wherever you are in the East Bay, count your blessings: There are gardeners in Winnipeg and New Mexico that would turn green with envy at gardens in our most unforgiving microclimates.
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