Many Southern California native trees offer vibrant fall colors

At this time of year, we tend to think of trees with colorful leaves as native to colder climates than ours. But then Jenny Iyer from the Riverside-Corona Resource Conservation District (RCRCD.org) comes along and reminds us that a large collection of California native species are garbed in foliar coats of many colors.

“Many Southern California natives offer great fall color,” she writes, listing “Fremont cottonwood (Populus fremontii), western sycamore (Platanus racemosa), willow species (Salix spp.), California black walnut (Juglans californica), western redbud (Cercis occidentalis) and fragrant sumac (Rhus aromatica). These are coloring up right now at the Riverside-Corona Resource Conservation District’s LandUse Learning Center demonstration garden in Riverside.” The center is located at 4500 Glenwood Drive and is open 8 a.m.-4 p.m. daily, except holidays, and admission is free.

Iyer informs me that, “The LandUse Learning Center demonstrates the three main land uses in Southern California: native habitats, urban areas and agriculture. The garden empowers visitors to make our urban and agricultural areas work more like healthy, functioning ecosystems.”

Let’s take a look at the trees Iyer mentions and the qualities that make them special.

Fremont cottonwood is a massive tree, growing up to 100 feet tall. It is probably not a candidate for backyard growing, unless you live on a ranch. Although its height presents a challenge, its proclivity to spread is also an issue. It has wandering roots that send up adventitious shoots. These shoots eventually turn into trees of their own, creating a clonal arboreal colony that is potentially without limit.

Quaking aspen (Populus tremuloides), native to California and other western states, is cottonwood’s most famous cousin. Its Pando colony (“Pando” meaning “I spread” in Latin) in central Utah encompasses 106 acres and 47,000 genetically identical trees, all of which are male. They are all males due to the dioecious nature (trees are either male or female) of plants in the botanical family (Salicaceae) that includes poplars and willows.

In any event, Pando is considered to be the most massive and, at 80,000 years old, the oldest living organism on earth. An ancient creosote bush (Larrea tridentata) clonal colony in the Lucerne Valley area of our own Mojave Desert is 11,700 years old, and it occupies second place in the contest of long-lived vegetative organisms. Next would be Methuselah, a bristlecone pine (Pinus longaeva) in the White Mountains above Death Valley at 4,800 years old followed by The President, a redwood (Sequoiadendron giganteum) in the Sierras that has lived for 3,200 years.

Western sycamore (Platanus racemosa) is the native tree of choice when it comes to migratory foliar aromas on hot summer days. The musky scent associated with many of our natives takes on a sweeter nuance in the case of California sycamores. In addition, their mottled trunks produce unpredictably dramatic, sculpted silhouettes as they mature.

Unfortunately, two fungal pests visit these trees and take away from their beauty. The first is powdery mildew, prevalent throughout the growing season, recognized by a fuzzy white layer on leaf surfaces, puckering the foliage. Anthracnose, on the other hand, is a fungus that is most active in spring, laying waste to canopies as burnt and crinkled foliage is the most visible symptom. These fungal conditions are found wherever sycamores grow, including in their Topanga Canyon habitat.

While these maladies may be treated with chemicals,  they are not life-threatening when ignored. Sycamores have strong immune systems and often live for several hundred years, despite the non-stop presence of fungus. The odd angles created between branches and trunk are the result of fungi disturbing bud development on young trees, leading to distorted growth on the part of young shoots that eventually turn into hefty, if strangely misdirected branches.

Many people consider redbuds, although their flowers are more pink than red, to be the most brilliant of all spring-flowering trees. In full bloom, they appear as blinding flashes of magenta-pink against a background of smooth gray branches. Before a single leaf appears, branches are studded with flowers. And if the flowers themselves are not sufficient to keep your interest, a display of heart-shaped leaves, with broad bronze margins, are soon to follow. Eventually, these leaves turn to a pleasant lime green and, in the fall, will change to gold, orange and red. Bees of every kind are attracted to its nectar-rich flowers and birds hunger for its leguminous seed pods. In fact, the flowers, young leaves and pods (when green) of redbuds may be eaten by human beings as well – in case you are hiking in the chaparral and need a snack. Avoid cutting the suckers that form around the base of your redbud tree. Redbud bark is thin and susceptible to cracking when exposed to direct sun so keep the bark protected by allowing suckers to grow.

California black walnut produces edible nuts, but they are significantly smaller than common English walnuts and have harder shells. There are two subspecies: californica is found mostly in Southern California and grows up to 30 feet tall with equal spread, while the other subspecies, hindsii, is found in Northern California and reaches twice the height of its southern counterpart. Hindsii has been used as a rootstock in commercial walnut orchards throughout the state. To review, nearly all fruit and nut trees consist of a rootstock, often grown from a seed, and a scion, which is grafted to the rootstock and bears the crop that we eat. Rootstocks are chosen for their disease resistance and the vigor they impart to the scion. California grows 99% of the walnuts produced in the United States on 400,000 acres, virtually all of which consist of trees whose rootstock is the California native walnut.

Before leaving the subject of foliage that undergoes a color change, we must pay homage to the pomegranate and the persimmon. Matthew Hunt, who gardens in San Clemente’s Talega community, wrote as follows: “Our pomegranate tree gives us reliable yellow leaves (with some brown mixed in) at about the same time as our ginkgo turns golden. Its fall color is not amazing, but it’s a pretty good bonus when you consider the additional aesthetic of its early fall fruit, to say nothing of its spring flowers.”

And Rolland Graham, who tends plants in Mission Viejo, sang the praises of another fruit tree in this manner: “In late November-early December, persimmon foliage changes to a brilliant yellow with red hues on some leaves, especially on the Fuyu variety. If not already harvested, the orange fruit provides a colorful complement. Once the leaves drop, the persimmons remain for several weeks as orange ornaments on the bare branches (unless the crows get to them first). It’s a truly spectacular display.” Graham also mentioned that his Hachiya persimmon is 50 years old, kept “trimmed to manage its height,” and yields a huge harvest every year.

California native of the week: The fragrant sumac (Rhus aromatica) in Riverside’s LandUse Learning Center has several outstanding characteristics. First is the lemon scent its foliage emits when crushed. Its stems are velvety, and it grows into a thicket 10 feet high and 10 feet wide and is highly touted for erosion control. It is deciduous and displays yellow flowers on stem terminals before leaves emerge in the spring. These leaves will eventually turn gold, red, and purple in the fall. Meanwhile, its red berries are highly attractive to wildlife. Its trifoliate leaves will remind you of poison oak to which it is related, except that it is not as dermatitic as that more infamous species. It will grow in any type of soil.

Do you have a special tree — whether for shade, ornament, or fruit — about which you would wish to enlighten others? If so, send its story to joshua@perfectplants.com. Your questions and comments as well as garden conundrums and successes are always welcome.