Now and then we Master Gardeners hear from a homeowner worried about her citrus tree because its leaves are yellowing.
A little yellowing of leaves in winter is not a concern, but a lot of yellowing, especially if the leaves also are dropping from the tree, is a bad sign.
I can’t cover in the space of this column all the possible reasons for yellow leaves on a citrus, but I will point out a few of the usual suspects. I encourage anyone who is concerned about a citrus tree that appears to be ailing to call our Master Gardener help line and describe in detail what is happening with your tree. The help line is 650-726-9059 ext. 107.
If the leaves are turning yellow and dropping, and there are no other symptoms of trouble on the tree, the likely culprit is over-watering. Citrus need a moist soil, but they are unhappy in soggy soil. Generally speaking, you don’t have to water until the first several inches of soil are dry.
If the leaves are turning pale green to yellow, but staying on the tree, the problem probably is a nutrient deficiency. Most likely the tree isn’t getting enough nitrogen. Citrus needs a lot of nitrogen to do well. A nitrogen-rich fertilizer is one in which the first of the three numbers on the label is higher than the other two (The first number corresponds to nitrogen). A 3-1-1 or 4-1-1 ratio is good.
Late winter or early spring is a great time to begin fertilizing your citrus.
Here are a few more things good to know about citrus:
• They need water year-round. With the dry winter we’re having, you might need to give your tree a deep soaking once a week this winter;
• They grow best in full sun (about eight hours a day of sun) and in daytime temperatures between 70 degrees and 90 degrees;
• Like every tree, keep its trunk dry when you water;
• If your tree is located in your lawn (and that’s not a great place for it) and you use a sprinkler to water your lawn, odds are the tree trunk is getting wet. You want to keep the trunk and the bud union dry (The bud union is where the top portion of the tree — the fruiting section — has been grafted on to the root stock. You’ll see a ring where they join); and
• A tree in the lawn also most likely is not getting enough water. Turf has shallow roots, a citrus tree’s roots extend down about two feet. Supplement the watering so that the tree gets a good, deep soaking.
Hope you enjoy the fruits of your labor for years to come!
Joan Tharp is a University of California Cooperative Extension Master Gardener. She lives in San Mateo. She can be reached at email@example.com.