Gardening in the foothills can be a fun, challenging or frustrating experience depending on what climate zone you are gardening in. Plants' irrigation and nutrient needs, flower and fruit production and susceptibility to various insects and diseases can all be influenced by weather and climate.
When standing in the middle of a nursery filled with beautiful plants, how do you choose which to take home? First, arm yourself with information about which plants are adapted or specific to your climate zone; your success growing them will be greatly increased. A climate zone is defined by such parameters as latitude, elevation, ocean and continental air influence, mountains and hills and temperature highs and lows. The vast majority of El Dorado County is in Sunset Zone 7 which the Sunset Western Garden Book describes as having hot summers and mild, but pronounced winters. Of course, your own property could have several different micro-climates too.
Plants at a nursery are usually labeled with the appropriate climate zone; if they aren't, ask the nursery personnel. Try not to be tempted into buying a greenhouse-raised plant from Sunset Zone 24, no matter how beautiful it looks. When you plant it expecting the same result, you will have wasted time and money, not to mention the frustration and disappointment experienced by looking at a once beautiful, now very dead plant outside your window. If you insist on buying plants outside your climate zone, be prepared to spend extra time and perhaps money replicating the plant's natural environment.
Temperature will play a primary role in fruit production in many fruit trees. A minimum number of hours below 45˚ F are required for many varieties of temperate fruit trees which is called a tree's chilling requirement. For example, most apple varieties require between 1200-1500 “chilling hours”. The decrease in daylight and temperature during fall causes a tree to enter dormancy due to the production of various growth inhibitors. In order for a tree to break dormancy (leaf out in spring), growth inhibitors within the tree must be broken down by sufficient exposure to cold temperatures. If a tree does not receive the minimum chilling requirement, delayed foliation will result along with delayed and extended bloom and an overall reduction in fruit quality and quantity. To reference the importance of climate zones, most of Northern California receives 800-1500 chilling hours each winter whereas Southern California receives only 100-400.
Some fruit tree species may have varieties that are bred for “low chilling” hours, these require fewer hours than standard varieties. These varieties are mainly bred for Southern California locations, rarely would a foothill gardener choose one of these varieties for our cooler climates. For example, ‘Anna’, ‘Beverly Hills’, and ‘Dorsett Golden’ are low-chill apple varieties, requiring fewer than 300 hours of chilling. Check with the nursery or use the University of California’s “California Backyard Orchard” website at http://homeorchard.ucdavis.edu to get information on chilling hour requirements (look under “Tree Selection” on the website).
For those interested in finding out exactly how many chill hours we have accumulated thus far this winter, the University of California has a wonderful resource: UC Fruit & Nut Research Information Center website at http://fruitsandnuts.ucdavis.edu. The website uses several formulas and local temperature data to calculate the number of chilling units accumulated. Go to “Weather Services” on the website to find how many chilling units we have accumulated based on the Camino weather station site (828 units below 45° from November 1 to February 1).
The California Irrigation Management Information System (CIMIS), established in 1982 as a joint project between UC Davis and the Department of Water Resources is another helpful website for local weather information. It consists of an integrated network of over a hundred weather stations located throughout the state; we have one right here in Camino! Each night, data is downloaded into the system and made available free of charge to anyone (registration is required on the site for statistical purposes only). The data include local evapotranspiration rates, precipitation, solar radiation, temperature of soil and air, dew point, wind speed, humidity, etc. and are available in hourly, daily, monthly and historical formats. You can access this season's chilling unit accumulation through links on the CIMIS site itself at http://www.cimis.water.ca.gov.
If this article has completely confused you (or made you crave more details), please visit us tomorrow, February 18, starting at 9 a.m. for a free Master Gardener class on "Weather & Climate in the Foothills." The location is at 311 Fair Lane in Placerville; no registration is needed. For information on this and any other home gardening subject, call our office at 621-5512 during the hours of 9 a.m. to noon, Monday through Friday; walkins are also welcome at the above address.
Tip: Do you have a yellow starthistle problem? If so, a workshop dealing with control of this noxious weed is scheduled for Friday, February 24, from 1 to 4:30 p.m. in the County Planning Commission Room (Bldg. C of the government center). Experts from the EDC Invasive Weed Management Group, UC Cooperative Extension and EDC Dept. of Agriculture will be leading this workshop. Call Nancy Starr at (530) 621-5552 for more information or to register; there is a $5 fee for materials.