BY JANET HARTIN -

Come Hear Dr. Mathews Speak This Saturday Before She Retires!

I am delighted and honored that Dr. Deborah Mathews, a plant pathologist at UC Riverside for over 30 years, is presenting the last lecture of her career for the beginning San Bernardino County Master Gardeners this Saturday, November 9!   While we do not have unlimited space for veteran, perennial, MGs, we have room for 5 or 6 of you to join the new class Saturday. Please email Joseph at jsalib@ucdavis.edu if you are a perennial MG and wish to attend this historical event and take part in a send-off. We will be bringing in a cake as well.

We meet from 1-4 PM at the Founders Recreation Center located at 2000 Founders Drive in Chino Hills. Remember that we do not meet at Grand Avenue Park anymore!

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After a couple recent trips to the East Coast and many memories of beautiful splashes of fall color from growing up in the Midwest and moving further north to attend University of Minnesota I remain in awe of the brilliant reds and oranges that many deciduous trees reward us with in the fall.

Did you ever wonder why trees ‘turn’ color in the fall? The short answer: It’s primarily a function of long cool fall nights and short sunny days.

The longer answer? Chlorophyll is responsible for the basic green color of leaves we see in spring and summer and is a necessary component of photosynthesis which uses sunlight to manufacture sugar (food) that is stored during the dormant period of the year. Carotenoids produce yellow, orange, and even brown pigments in crops such as carrots, squash, bananas, and many ornamentals such as daffodils and poppies. Anthocyanins are red and orange in color and are most linked to lavish displays of brilliant fall foliage. They also give rise to coloring of strawberries, plums, and cherries.

Here’s the kicker; while chlorophyll and carotenoids are present in leaf cell chloroplasts throughout the entire growing season, most anthocyanins are only produced in fall due to bright light and excess plant sugars within leaf cells.

So, in reality foliage doesn’t ‘turn’ orange or red at all. Carotenoids and anthocyanins are always in the leaves; they are simply unmasked once the active growing season is finished and chlorophyll is no longer produced. This happens when nights lengthen in fall.

Interestingly, the actual timing of color change varies across species and appears to be genetically inherited. The same species will exhibit a similar color scheme in cool temperatures in higher elevations at nearly the same time as it does in warmer lower elevation climates. The intensity can vary quite a bit however.

Where do temperatures enter the picture? Both the amount of color and the overall intensity of fall color is very linked to weather conditions that occur prior to and during the actual time the chlorophyll in leaves winds down. The most brilliant displays occur after several warm, sunny days and cool, crisp (above freezing however) nights. This is because although lots of sugars are made in leaves during sunny daytime hours the corresponding cool nights prevent the sugars from moving out. The amount of soil moisture also helps ensure that from year to year fall colors vary even in the same trees. So, either aA late spring or a prolonged drought can both delay the display of fall color by a few days or even a few weeks. What’s the recipe for the most brilliant fall display? Most likely a warm moist spring followed by a warm summer and sunny fall with cool autumn nights. .

Although fall color is not nearly as spectacular in lower elevations of Southern California compared to other colder areas of the nation, the Liquidambar or American sweet gum (Liquidambar styraciflua) offers some pretty impressive fall color and an impressive 300- 400-year life span. (Did you know that liquidambar got its name because it at one time was a sought-after chewing gum for Native Americans?)

To help guarantee vivid colors for years to come, growers carefully propagate trees by cuttings to yield identical clones that will produce just as brilliant fall foliage as their parents. You may have come across the popular cultivar named Festival or even have one in your own yard. I like it because it stays more compact and columnar than most liquidambars. The downside? It is less cold tolerant than other liquidambars but does well in most warmer areas of Southern California.

The cultivar Moraine is broader and a better choice if one has adequate space for a shade tree; it is also adapted to cooler temperatures and it rewards homeowners and passer-byers alike with beautiful red fall foliage.

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Enjoy the rest of the week!

Janet