Source:
http://www.sacbee.com/107/story/545439.html
Garden Detective: Sick citrus needs smart watering schedule
Published 12:00 am PST Saturday, December 8, 2007
Story appeared in unknown section, Page CALIFORNIA LIFE9
Q: The older leaves on my dwarf kumquat tree have turned a lighter green with blotches of pale yellow. It's 2 to 3 years old, grows in a pot on my deck, gets fertilizer regularly and has lots of new growth. I can't put it in the ground since the deer eat everything. Am I watering it too much or not enough, or giving it too much fertilizer?
A: Evergreen trees go through periods when they drop leaves excessively, says Sacramento County UC master gardener Bill Pierce. Healthy citrus leaves are dark green; they turn pale green when the tree is low in nitrogen.
When the leaves turn yellow but the veins stay green, the tree needs iron. Since you use citrus fertilizer, your tree should not show nutritional deficiencies.
Excessive irrigation also causes leaves to yellow and drop. Just sticking your finger an inch or so into the soil will tell you if water is needed, or you can purchase a moisture meter to use in planning this tree's irrigation needs.
Here is a watering schedule that might help:
During the rainy season, water only when there are long rainless periods.
During the cool spring and fall weather, water once a week.
As the weather warms, water two to three times per week.
When the temperature hits 100 or higher, water every day.
By shading your container from the afternoon sun, less water will be needed because the evaporation rate through the container will decrease.
Also, a 3- to 4-inch layer of mulch in the pot will help keep the soil and roots cooler. Keep the mulch at least 4 inches away from the trunk of the tree.
Joe's comments: During winter, most lemons, fortunellas and their hybrids will always show yellowing or splotches of it, if the trees are planted inground outdoors. This has got to do with near dormant metabolism of the roots when temperature is low but then the winters are interspersed with warm days. Since the soil temperature does not vary as much as air, when there is demand for nutrients, the roots cannot metabolize and transport them quickly enough for the changing daily needs of the above ground parts during short warm spells, thus the result is shown as nutrient deficiencies even if your soils are rich with all nutrients. One way to remedy the situation if you are unforgiving when it comes to dark green perfect foliage is to apply foliar sprays of nutrients during the warm spells of the winter. But as for me, there is no need, the leaves will all regreen or darken come the first warm days of spring.
