November 15, 2001

Autumn

                                                 

People not from around here are fond of saying we don’t have seasons in Southern California. That is, of course, ridiculous. You just have to be more observant. In late August and early September, a subtle change comes over our surroundings. And I don’t just mean the summer movie season is over. From time to time a sudden, fresh zephyr blows in the back office door, knocks a few papers off my desk, and exits through the front. Spiders are evident, the big fat orb weavers of Halloween fame. Lots of grasshopper nymphs in various shades of green and grey hop around explosively while the few adults bask on swelling sage buds. The crows are getting restless, smaller birds gather on the power lines draped above the street. Year-round gardeners cheer on their favorites in the slanting sunshine: the warm season team has bloomed and gone to seed, while the cool season team is just beginning to wake up and stretch its sprouts.

On July 1, back in the fat of summer, we had 14 hrs and 44 minutes of sunlight. By September 30, only 8 days into autumn, we’ll enjoy only 11 hrs and 49 minutes of day. That is almost three hours, or 20%, less illumination than in July. Many plants are keyed to what is called critical night length, which is a specific number of hours of continuous darkness. This internal clock then signals these plants to bloom, for instance. Shorter days mean cooler temperatures, and a drastic change in environment for plants, which derive their energy from sunlight. As autumn unfolds, long-day-length plants have already produced seed and the season’s growth, and are now hardening and hunkering down for winter’s chill and lack of sun. Their metabolic processes can’t produce energy enough for growth from the meager winter sun, so they go dormant. Some drop their leaves, such as locally admired liquidambar, ginkgo, pistache, and crepe myrtle. Others, the evergreen broadleafs, suspend operations for a few months. Meanwhile, cool season plants have adapted to take advantage of the resources suddenly made available by their competitors’ dormancy. They begin a growth spurt in autumn, and observe their dormancy in summer. Many of our California native plants follow this pattern, because we receive almost no rain in summer.  

Among animals, adaptations have developed to take advantage of niches of resources to best support the species’ survival throughout the seasons. Many insects over winter as eggs, so of course in autumn, high priority activities for survival are maturation, mating, and egg laying. You’ll see lots of adult grasshoppers around now, doing adult grasshopper things, while the nymphs are off somewhere in the bushes, eating.   Migratory birds are beginning to return to their over wintering grounds, after nesting in the north where the longer summer daylight hours allow them more time to seek food for their nestlings. Among mammals, the summer beachgoers have abandoned the shoreline, leaving plenty of parking space and prime sand for the sometimes testy off-season visitors.

Since gardening goes on year-round in our area, our rhythms and activities are affected by day length changes as well as the changes in the plants we attend to. There are more leaves to rake, but fewer spent flowers to trim. It’s tempting to linger at the coffee shop as the mornings become darker and cooler. But the grass grows all year, and the insects aren’t asleep yet. Autumn here is the best time for planting everything except tropicals, bareroots, and warm season annuals. So, we remind our gardeners to limit their donut time, get out there and enjoy everything that southern California autumn has to offer, including those piles of colorful leaves. See if you can define the moment when you feel, through the signs in the environment, when autumn has arrived in Orange County.

 
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