THE COASTAL GARDENER:

Three weeks ago nighttime low temperatures fluctuated between 50 and 56 degrees. Two weeks ago, night temperatures were 43 to 46 degrees; a little chilly. Last week, the mercury dropped further and hit a low of 37 degrees — downright cold. That’s almost a 20-degree change in nighttime temperature in only three weeks. For the plants in your garden, that’s a bit like taking a drive from Palm Springs to Idyllwild.

In my own potted-plant collection I have divided each plant as either a cool-season grower or warm-season grower. Cool-season plants are happy from fall through spring, while warm-season plants prefer spring to fall. I even insert a blue plastic plant tag into the pots of my cool-season plants and a red tag into the edge of the warm-season pots.

This helps remind me when to water, when to fertilize, when to expect growth and flowers and when not to.

Just a couple of weeks ago I was noticing how most of my warm-season plants were still looking quite happy.

The leaves were even then green, strong and sturdy. My summer flowers, bulbs, perennials and shrubs were still quite happy.

This is the illusion to which Orange County nongardeners fall victim. Believing all their plants should be glorious, vibrant and blooming every day of the year, they engage in watering and fertilizing, regardless of season, in an errant attempt to trick nature and the plants themselves.

Yes, we are blessed with fabulous gardens that could very easily be in flower all year. On closer inspection, however, we find that it is not the same plants that are forever the stars of the show.

A well-crafted garden, like a well-crafted stage production, features different performers at different moments throughout its performance.

Now, back in my garden, just a few weeks after marveling at my warm-season plants, these same performers have developed yellow leaves and limp foliage. New growth has stopped, and flower buds — if there were any — have fallen.

Night temperatures, having dropped from the fifties into the 30s, are the culprit. The curtain has closed on the warm-season act.

Obviously, temperature affects the productivity and growth of plants, but this varies depending upon whether the plant is a warm-season or cool-season variety. For instance, if temperatures are high and day length is long, cool-season plants like cabbage, lettuce and spinach will go to flower, rather than produce leaves. If temperatures are too low, warm-season crops like tomatoes and peppers will not set fruit.

During mid summer, temperatures could actually be too high for warm-season plants like tomatoes or peppers, causing pollen to become sterile and stopping flower pollination.

By mid December our dilemma is low temperatures, which results in poor growth of warm-season plants. Photosynthesis slows at these lower temperatures. When photosynthesis is slowed, growth is slowed. With no new growth there are no flowers, and leaves turn yellow.

But in some cases, even warm-season plants need a cool period to grow properly. This is true of crops growing in cold regions of the world and explains why we cannot grow a decent peony, lilac or pear tree in Newport Beach or Costa Mesa.

Consider popular market fruits like Elberta peach, Red Delicious apple and Bartlett pear. All of these require about 800 or 900 hours of temperatures below 45°F and above 32°F before they break their rest period and begin flowering. If this cold requirement is not met, then sparse, small and misshapen leaves will result and the trees will not set fruit. Other warm-season plants that need a long winter chill are peonies, lilacs, forsythia, crab apples, flowering cherries, rhubarb and most tulips.

As curious coastal gardeners, when we understand the unbendable rhythms and cycles of the plants in our gardens we also find increased satisfaction in our efforts. Our nights have quickly turned cool, there a now yellow leaves on some plants, and some others have ceased flowering. But others have awoken, are growing quickly and are in glorious bloom.

Coastal gardeners are fortunate. Yes, our gardens are beautiful all year. We just need to understand them a little better.

ASK RON

Question: What is the best time to broadcast seeds of California Poppies in my garden?

Vicky

Newport Beach

Answer: The months of November or December are perfect. I suggest mixing the seed with a cup or so of sharp sand, like silica. Shake the mixture for a minute or two and then broadcast evenly. The sand will scratch the seed a bit, improving germination and will make it easier to distribute the small seeds. I also suggest sowing the poppies just before a slow-moving storm that will offer several days of moisture and clouds. Nature will germinate most of the seeds for you and reduce your need to water as much.

ASK RON your toughest gardening questions, and the expert nursery staff at Roger’s Gardens will come up with an answer. Please include your name, phone number and city, and limit queries to 30 words or fewer. E-mail stumpthegardener@rogersgardens.com, or write to Plant Talk at Roger’s Gardens, 2301 San Joaquin Hills Road, Corona del Mar, CA 92625.

RON VANDERHOFF is the Nursery Manager at Roger’s Gardens in Corona del Mar.