It is always exciting to pick out new trees for your property, but there’s more to proper species selection than many people commonly suppose. For example, many homeowners and property managers rely solely on the USDA Hardiness Zone of their area to filter their possible choices. But while your local hardiness zone is an important factor to consider when deciding on the best trees for your property, there are plenty of other things you’ll want to factor into your selection algebra.
What Are USDA Hardiness Zones?
Hardiness zones are mapped out regions of the United States, which are created based on a single criterion: the annual low temperature. The zones are each designated by a number and a letter, with each number representing a 10-degree range, and each letter representing a 5-degree subdivision.
For example, places in USDA Hardiness Zone 9a experience winter lows of between 20 and 25 degrees Fahrenheit, while those in USDA Hardiness Zone 9b experience winter lows between 25 and 30 degrees Fahrenheit. Most portions of southern California are classified in USDA Hardiness Zones 8a through 10b (see full map of California’s hardiness zones here).
Yet while low winter temperatures are clearly an important consideration, they leave plenty of important information out. Sunset Zones are another useful classification scheme, whichare formed with more information than USDA Hardiness Zones are. Created by Sunset Magazine, Sunset Zones also consider things like humidity, length of the growing season and large-scale wind patterns to provide a clearer picture of your local growing conditions. Most regions of southern Californiaare classified in Sunset Zones 18 through 24.
However, they still fail to take into consideration plenty of other important criteria that will influence your new tree’s chances of survival.
Additional Considerations for Tree Selection
Don’t misunderstand: USDA Hardiness Zones and Sunset Zones are fantastic tools, which can help you rule out inappropriate species at the outset of your selection process. However, you’ll also want to consider the following criteria when selecting trees for your property.
California may be known as the Sunshine State, but that doesn’t necessarily mean your property enjoys full sun exposure. Your home, your neighbor’s trees and a number of other things can all created vast shaded areas. Some trees will thrive in these partially shaded areas, but you must be sure to choose those that can tolerate low light levels.
Even native species, which are obviously well-suited for the southern California climate, may not thrive in your yard if you lack the space to properly host them. Accordingly, you’ll want to carefully assess the amount of space available, and choose a tree suitably sized for it. While you should definitely consider the height of any potential tree you select, it is more important to consider the tree’s spread.
Even if your geographic area receives ample rainfall, the local drainage patterns and hardscapes can alter the way water flows across the surface. This can leave some small areas within your property bereft of enough rain, while other areas may remain relatively damp all year long.
A variety of native and invasive pests plague southern California, and you’ll need to avoid picking trees that are vulnerable to the local threats. Some invasive pests also exhibit very localized distributions, meaning that someone at one end of a zip code may plant vulnerable trees with impunity, while others must avoid doing so entirely.
Even though the basic soil characteristics of a region change over the course of miles, small changes in chemistry, structure and composition often manifest over much smaller scales. This is because the large-scale soil characteristics are determined by the long-term geology and climate of the region, while the small-scale characteristics are chiefly the result of the ways humans have interacted with the land over the past few decades or centuries.
Sunset Zones consider large-scale wind patterns when devising their classifications, but they can’t possibly account for the fact that your yard is right next to a cliff, busy highway or open field – all of which can alter the local wind patterns. Most trees can adapt to relatively strong winds (particularly if these winds tend to blow in a single direction), but different trees withstand wind to different degrees, and you’ll need to consider the winds of your area before making your choice.
Most trees will grow in pristine, virgin wilderness areas, but only a select few will thrive in polluted, urban areas. This isn’t as big of a consideration for those living in rural areas (although local farms can have a damaging effect on these areas), but those living in the city must consider the ability of any tree considered to withstand polluted air and water.
Again, Sunset and Hardiness Zones can provide valuable information, and they should factor into your selection process. But it is important to look beyond these classifications, and weigh the tree’s needs against the specific characteristics of your yard.
If you’d like some help selecting the best trees for your property, contact your friends at Evergreen Arborist Consultants. Whether you live in Malibu, Beverly Hills, Pasadena or anywhere else in the greater Los Angeles Area, we’ll send out one of our certified arborists to analyze the local conditions and make recommendations for your new installation project.