You know when you walk out the door how hot or cold it is, how windy, shady, moist or dry. You know if your soil is pure sand or hard clay because you’ve dug a few holes in your time. You don’t need a book to tell you these things. So why are the gardening zones described in Sunset Western Gardening book important when you add a new plant to your garden ? And why are they so confusing in our area?
I hear it all the time when garden consulting. “What zone am I?” “My plants keep dying, what can I do?”
The growing conditions in your garden determine how successful your plants will be. Besides weather and climate your soil affects how plants grow.
For decades, climatic data has been compiled and maps generated to help make sense of local growing conditions. In the 1930s, Sunset Magazine began mapping the western states, taking into consideration the unique climatic growing conditions along with the traditional data of minimum and maximum temperatures, latitude, elevation, ocean influence, continental air influence, mountains and hills and the local topography.
Today the map has become known by many as the gold standard for western growing advice. Zones are numbered from the harshest (Zone 1) in the north to the mildest (Zone 33) in the south.
To accompany the map a plant encyclopedia was developed that assigned the appropriate zone(s) for each plant. The system helps take some of the guesswork out of plant selection if you take into account your microclimate and how your garden differs from areas close by.
Soil quality is not taken into consideration in zone mapping. Since the soil houses the water and nutrient uptake system for most plants, it plays an important role. Most plant guides describe soil requirements in terms of well-drained, acid or alkaline, poorly drained or high organic matter. Many soils can be modified with amendments or by the use of raised beds.
The zone system isn’t perfect. After all, the data collectors don’t live here in our neck of the woods. We are unique and they are looking at the entire western United States. Still, it’s a good idea to take a look at the Sunset zone you live in to see if a plant might survive in your garden but keep these exceptions in mind.
We really only garden in three zones around here – zone 15, 16 and 17. With each new edition of Sunset’s Western Garden Book I eagerly look to see if they’ve figured out that Felton is not in zone 7 but they haven’t done so yet.
The Sunset map shows Felton as being in zone 7 and described as a ridge top instead of on the valley floor. This is the most confusing part of the map in the current edition of Western Gardening. Based on my experience even ridge tops like the highest portions of Bonny Doon and the Summit area that get an occasional dusting of snow fall mostly in a colder zone 15. Zone 7 areas like the Sierra foothills have a much colder winter cold average than any place around here. It’s confusing to both new and seasoned gardeners alike. Here are some tips to help you determine in what zone you garden.
Zone 15 – this zone encompasses most of our area. Winter lows average 20-30 degrees although we are trending toward warmer winters these last few years. The valley floor of both San Lorenzo and Scotts Valley lie in this zone and are what I call “a cold 15”. Cold air sinks and is trapped in these areas. Often there is damage to the tips of oleanders and citrus and fancy succulents need extra protection. There are warmer parts of this zone though where the growing season starts in March and ends in November. These areas rarely get a freeze after March 15th or before Thanksgiving. This zone is influenced by marine air approximately 85 percent of the time and the remaining 15 percent of the time by inland air. In general this zone has a moist atmosphere, cool summers and mild winters. Afternoon winds are common. Lows over a 20-year period ranged from 21 to 28 degrees.
Zone 16 – those who live up off the valley floor but below ridge tops live in this “banana belt”. Pasatiempo also falls in this thermal zone. Light frost can occur during the winter but mostly the winter lows in this zone stay above freezing. The area has a temperate feel from the combination of thermal belts and the coastal influence, with summers warmer than Zone 17 and winters warmer than Zone 15.
Zone 17 – This zone hugs the coastline on the west side of Highway One. Mild wet usually frostless winters are accompanied by almost daily blankets of fog.
Beside the zone you also need to note how much sun or shade you get during the growing season- April through September. Most plants can survive without sun during the winter as they are either dormant or semi-dormant but need good drainage. It’s those areas that get a blast of sun from about 11 am to 4 pm in the summer that you need to plan for more carefully.
There may also be microclimates on your property. Are you near the river in a canyon or gulch or up on a south facing slope? Some areas in your garden may be several degrees warmer than other spots such as up against a brick wall or at the top of a slope from where cold air drains. Planting a citrus at the top of a slope that drains away the cold will make your tree much happier than if planted in a low open area.
If you have questions about which zone you are in, email me and I’d be happy to help. I hope this helps in choosing plants that will thrive in your garden.