By Robin Y Rivet.
I’m ‘fessing up. I get too many calls to identify commonly cultivated tree species, but the task is daunting due to the marginal photographs that typically accompany these requests. Too many experienced gardeners seem to expect miracles in identifying trees from hastily snapped images. Even tree experts can’t ID plants from blurry images taken at a distance, or from close-ups that are just a mass of overlapping foliage – especially if taken in poor light.
Here’s some steps to consider before you call an arborist for ID help.
· Know your Sunset Western Climate Zone.
· Take precise pictures as possible (see this example for what to photograph).
o Upper and underside of leaves, that include stem attachments.
o Are the leaves arranged opposite or alternately on limbs?
o Look for buds, flowers, seeds, fruits or fallen litter; these are vital - even if dried out.
o Bark is highly variable, so look high and low on the tree for examples.
o Step back to see silhouette and describe it.
§ Excurrent? (cone shaped)
§ Decurrent? (rounded or umbrella-like)
· Estimate the height, width and possible age of the tree
o Use human scale EX: (~five human body lengths) or ~30’.
o HINT* – power lines typically run between crossbars at ~ 35’.
o How wide is the canopy?
o Is it naturally occurring, or clearly planted residentially?
· Growing conditions: is it healthy, irrigated, or poorly pruned?
· Is it in a yard, city park, or natural area?
Observe leaf shape, veins, and edges of leaves, and measure everything.
This site walks you through specifics. Here’s the best CA urban tree key and anyone who is motivated - can use it successfully. It was developed at Cal-Poly SLO and includes many commonly cultivated species. This tree site has an interesting video. Admittedly, none of this is easy. However, it is possible to key out ~85% of local tree genus using simple tools. Once you know it’s an oak, an expert might be more willing to help you further. With a few tips, you can be on your way to confident tree identification. It can be fun too – especially if you love plants. Unfortunately, National tree key websites like Arbor Day Foundation miss the SoCal boat. Our Mediterranean climatessupport too many species - not grown anywhere else.
However, if you think your tree is a California native, it gets easier. There are several websites with excellent images of diagnostic foliage, seeds, bark and structure of native trees. Calscape is a good place to start, and Calfora's another. Pines can be especially challenging, but California pine cones are cool to compare. Acorns too. Fruit tree cultivars are extremely difficult to ID without DNA analysis or historic records. So, when you purchase a fruit tree; write down its name, date planted and rootstock. Record: ‘Snow Queen’ nectarine - grafted onto “citation” rootstock – planted 3/2021. Someday your heirs will thank you.
And, if you’re really curious, but befuddled by the vast diversity of eucalyptus species in California, this Australian website might just be what you need - IF you have ample time for study. I find it fascinating.