Printed in the Davis Enterprise, November 2003
The recent recall election* demonstrated that California is divided: not along the North/South axis so many folks perceive, but East/West, or Coast/Interior. All of the counties that voted against the recall were coastal
except our own, and the vote that carried Yolo County for Gray Davis was, of course, Davis.
This division also applies to our water supply: nearly all of the water for our biggest cities comes from eastern California or parts further inland. Los Angeles "steals" water from Mono Lake and Owens Valley; San Diego has been using un-allocated Colorado River water for decades, and San Franciscos water travels westward hundreds of miles from the Hetch Hetchy Reservoir, which was created by damming one of the most beautiful river valleys in the state.
One of Enterprise columnist Bob Dunnings correspondents noted that the voting in Yolo County followed the climate zones listed in the Sunset Western Garden Book. Bob dismissed this observation with the comment "theres not a bit of difference between the climates in Woodland and Davis." Ah, but Bob is wrong (only on this issue, of course). There ARE regional differences in climate, as well as in soil type and quality, which affect how we garden.
The USDA has the US broken down into 10 plant hardiness zones based on average minimum annual temperature. Maps of these zones can be found at the US National Arboretum web site. Davis, Woodland, and Sacramento are all in USDA Zone 9b: average winter lows 25 30F, a zone we share with Brownsville, TX, Tucson, AZ, and Fort Pierce, FL (inland, west of Orlando). You can see the limitations of this system: it indicates which plants might survive the winter, but doesnt factor in heat, ocean influences, or wind.
Sunset Western Garden Book Zones
Davis is in Sunset Zone 14. The map for 14 shows the reach of the delta breeze, our natural air conditioner which makes this side of the Valley livable in the summer. Because of the coastal mountain range, that breeze is less likely to reach Woodland (Zone 8), Winters (Zone 9), or Fair Oaks (Zone 9) than it is to reach Davis, Modesto, or Stocktonall in Zone 14.
So Zone 14 differs in how early it cools in the evening (not how hot it gets!) in the summer. On one very hot summer day I drove from Woodland to my home near Dixon at about 6 p.m. The temperature in Woodland was 105, with no wind; when I got home it was 95 and breezy. That marine influence has some effect on winter temperatures, though mostly in the western end of the zone: the closer to the ocean, the milder the winter.
Zones 8 and 9 differ primarily by topography:
cold air drains from zone 9 down to zone 8. A cold frosty night is colder and frostier in Zone 8, so sensitive plants such as young Citrus, Bougainvilleas, tropical Hibiscus, and Brugmansia will benefit from extra protection. The microclimates around your house can provide enough protection to overcome this regional difference: the south or east side, under an overhang, will be a few degrees warmer than a spot just a few feet away. Development can change the climate zone: mature trees and concrete trap heat, while homes in outlying areas are more exposed.
Once you know the Sunset zones, you can guess what measures will be needed for a plant NOT listed for this area. Zones 15 17 are the Bay Area; those plants will need extra frost protection, more soil moisture, and higher humidity (e.g., Fuchsias). Zones 21 24 are Southern California; those plants are unlikely to survive any winter here (e.g., Mandevilla hybrids). They would need to be brought indoors by Halloween, and kept inside until mid-March.
Plants listed only for Zones 1 7 need distinct winter chilling to break dormancy. Some plants are just on the edge of that requirement here: peonies (Paeonia) and lilacs (Syringa) usually get enough cold to bloom well, but should not be planted close to the house where warmth might inhibit dormancy. Trees listed only for colder zones often dont grow at lower elevations, perhaps due to a requirement for winter chill, intolerance of prolonged heat or low humidity, or susceptibility to diseases which are not prevalent in their native ranges.
Other regional differences: wind and soil.
Wind comes from the southwest (delta breeze) or north more than 90% of the time here.
Wind from due west is rare, and from due east bodes ill as it usually occurs only under an extreme high pressure ridge. These rare interior winds are very dry and cold in winter (the freeze of 98 began as cold air drained down into the valley from Nevada).
Our infamous north winds are also dry, usually happen in March and October, and they may be twice as strong here as in Sacramento as they sweep down the valley. We can expect 2 3 days of gusts up to 30 40 mph, toppling trees, breaking limbs, stirring dust and pollen, and making certain individuals especially cranky (you know who you are). The south wind can be strong, though usually less gusty, and is certainly a factor for gardeners outside of Dixon or Davis on the west side.
Folks selecting trees in outlying areas should consider branch structure and the likelihood of limb breakage. Locusts (Robinia), Chinese elms (Ulmus parvifolia), and Bradford pears (Pyrus calleryana Bradford) are examples of trees to avoid in windy areas.
We live in a floodplain with mineral soils that have very little naturally occurring organic material. As floodwaters settled they would deposit sand, silt, and clay particles, which are ever-smaller bits of rock (in that order). In general, the closer you are to a creek or an old slough, the more sand you have; the further away, the more silt and clay you have. The more clay, the more youll need to work to enhance drainage for some plants. Adding organic material and elevating the soil into mounds or raised planters can overcome the drawbacks of clay soil.
Soils on the west and north sides of Davis have more clay, with Stonegate and Covell Park the heaviest and most difficult to manage. Layering of these soils during subdivision and the importation of fill have created additional drainage problems there. Drain systems can carry off excess water, and proper watering is key to successful gardening. Clay soils have the advantage of retaining moisture, so watering should be less frequent than in faster-draining soils.
The soils in North Davis Meadows and Binning Tract (near the Davis golf course) are even heavier and require careful irrigation managementwater should be applied slowly, deeply, and infrequently. There are some pockets of salinity in north Davis -- along Covell Blvd., Anderson Rd., up F Street north of Covellwhich lead to chronic yellowing and marginal leaf burn on sensitive plants. Looking to buy a home based on soil type? Old Willowbank has the best soil in the world: a fine sandy loam. Of course, those homes mostly sell by word of mouth
. East and Central Davis, as well as South Davis and El Macero, have siltier soils with better drainage than the north or west sides of town.
Does voting pattern correspond to climate? The closer you are to the ocean, the more moderate your climate....We'll just have to check and see how they voted in Modesto and Stockton.
[*This comment refers to the historic gubernatorial recall election of November 2003, in which voters ousted Gray Davis and voted in actor Arnold Schwarzenegger.]
© 2008 Don Shor, Redwood Barn Nursery, Inc., 1607 Fifth Street, Davis, Ca 95616
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