Chlorotic leaf from an Improved Meyers citrus tree

Conventional wisdom says that California is a gardening paradise. According to the zone maps, one can grow whatever plant they desire within our state’s boundaries (yes, even a coconut if you happen to live on the Pacific Coast Highway in Newport Beach). As I write this on February 4, the high will be 75°F (23.8°C) on the southern California coast with inland locations reaching the low 80s (upper 20s C). If you live in central or southern Florida, Hawai’i, or in the Southern Hemisphere where it’s summer now, this is not a big deal. But for the majority of North Americans and Europeans, the today’s weather forecast is usually envied. Being the “glass half-full” kind of guy that I am, there is a flipside to our warmer than normal kind of winter if you are a gardener—especially if you love tropicals. This is the time of year we deal with “yellowing”.

Now I’m not talking about the lethal kind that afflicts palm trees in other parts of the world. The yellow I’m referring to is the sickly, dull, chartreuse that plants exhibit in California this time of year. Winter is usually tough on warm-climate plants in California unless, of course, the flora is native to a similar dry summer/warm winter (Mediterranean) or desert area. Even then, many get a pale 1970’s-like refrigerator avocado color in the leaves even though the plants are not avocados.

The causes for this are many and some are obvious. First, (of course) is that it’s just plain colder that these plants would like it. While we may be frost-free in many parts of the SoCal coast, we get colder nights and days and for a longer duration than other subtropical climates. Plants simply say, “it’s too freaking cold, I’m not going to die but I’ll pack it in until the nights warm up.” In other words, plants cells go dormant and leaves go dull. My favorite line is that your refrigerator is technically a USDA Zone 10, but you couldn’t grow anything in it.

Yellowing kentia palm (Howea Forsteriana) frond. Note the UFO in the upper left corner.

To add insult to injury, the prolonged “cool” exacerbates other challenges that SoCal gardeners face. There’s the salt air near the coast which definitely has an effect akin to sandpapering your skin and pouring alcohol on it. As if salt in the air wasn’t bad enough, we get more than our share of salt in our irrigation water, much of it imported from the Colorado River. Now you don’t need to be an geographer to know that the Colorado is the reason the Grand Canyon exists—and is still being sculpted to this day. Those really cool looking rainbow-hued layers have to go somewhere and, you guessed it, it’s in the soil your palm trees are planted in.

You’d think that all these minerals in our water would at least deposit some iron in the soil which is required for plants to photosynthesize and, in turn, stay green. Well, maybe it does but I wouldn’t know by the yellow plants I have. Another cause for yellowing leaves is what plant geeks call chlorosis which is a fancy word meaning anemia for plants. Do you remember the last shampoo and conditioner commercial you saw on TV and how they threw the term “pH” like it means something for you hair? Well, it also means something for your soil too. If the soil pH is too high (i.e., basic), you can have a ton of steel wool, nails, and Geritol composted into the dirt but the plant roots will not uptake the iron. This, of course, results in more leaf yellowing.

But wait, there’s more…. Stay tuned.

Tags: Calfornia Gardening, Plant Disease, Plant Rant

This entry was posted on Wednesday, February 4th, 2009 at 11:08 by spectre and is filed under California Gardening, Horticulture, Plant Diseases, Plant Rant. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.