During the winter of 2014, which was extremely dry and cold, I lost my sweet little young Meyer lemon. I was flummoxed as to the reason. Yes, I had listened to the frost predictions and conscientiously covered the tree during the nights the low temperatures were predicted. Yes, I had augmented this arrangement with outdoor-certified extension cords and flood lights to create heat.
When the sun came up in the morning, I removed the coverings and turned off the lights to allow the tree and the soil beneath it to absorb as much daylight and ambient daytime heat as they could. What had I done wrong?
My poor tree was so stressed from lack of water that it didn't stand a chance. I had stopped irrigating in November and never gave it a second thought. But think back to that winter. We had very light precipitation and frequent frosts. Being a baby, the tree had no reserves.Faced with the lack of water and the cold, it could not cope.
I have since decided that the tree's location was not the optimum choice. Napa Valley is blessed with a mediterranean climate, characterized by mild, wet winters; mostly prevailing westerly winds; and warm, dry summers. Coupled with the many micro-climates in our gardens, this weather allows us some options for placing citrus trees.
Microclimates are the distinctive climates zones within your garden. At the end of a hot day, walk around your garden after the sun has gone down. I did this recently when I took the dog out late at night. As I walked by the west-facing side of our stucco house at midnight, the day's heat was still radiating off of it. Any frost-sensitive citrus tree would love living there. So choose a west- or south-facing location, preferably against a wall or fence that will capture and return the daytime heat.
Frost protection is a major issue with citrus. Stay informed about the weather and be prepared. Keep tender plants hydrated, and keep the area beneath your citrus trees' canopies free of mulch or any cover. This will allow the soil to absorb heat during the day, and after the sun goes down, the rising heat will warm the trees.
Cover your citrus when frost threatens to protect delicate foliage. The entire neighborhood gets to see my taste in linens because I use old sheets, but a cloth tarp works, too. Plastic isn't recommended as it does not breathe. Try to keep the cover off of the foliage by draping it over some kind of structure. If the cover touches foliage, those leaves may freeze. Uncover when the sun comes up.
Christmas tree lights (the old-fashioned type, not LED) can add a few degrees of protection. Drape them around the trunk and branches, or place a large spotlight on the ground under the cover. Use only outdoor-rated lighting and cords.
Citrus have shallow roots that are easily damaged, so plant them where the soil does not get disturbed. Monitor soil moisture even in winter. Don't allow container-grown trees to dry out completely.
Consider growing citrus in containers to have more location options. You can put wheels on the pot and position the tree in your best location to take advantage of microclimates. Container-grown citrus needs to be transplanted every three to four years and monitored closely for nutrient deficiencies.
Choose the citrus varieties best suited to your area. Check for pests frequently. Feed regularly to keep the foliage green and the fruit coming, especially with young trees.
Fifteen years ago, the citrus leaf miner turned up in California citrus. Recently,citrus greening disease has become a huge concern for California growers. Be aware of these pests and diseases and be proactive in caring for your trees. For more information, consult the University of California Agriculture and Natural Resources web page (www.ucanr.edu), using the key phrase “citrus.”
Workshop: U. C. Master Gardeners of Napa County will host a workshop on citrus on Saturday, October 24, from 9:30 a.m. to 11:30 a.m., at the University of California Cooperative Extension Office (address below). This workshop will focus exclusively on caring for citrus, large and small. Potting and repotting container citrus, pruning, watering and fertilizing, frost protection and recovery from frost damage are part of the program. The workshop will also cover using the University of California IPM website to identify and understand citrus diseases and pests. Online registration (credit card only); Mail-in registration (cash or check only).
Workshop: U. C. Master Gardeners of Napa County will host a workshop on El Niño on Saturday, October 31, from 9:30 a.m. to 11:30 a.m., at the University of California Cooperative Extension Office (address below). An El Niño winter is on the horizon, no doubt about it. Napa County could well see heavier than average rainfall. This workshop will focus on measures to take now to prepare your home and garden for heavy rain. You will also learn steps to take during and after a flood.Online registration (credit card only)Mail-in registration (cash or check only).
Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. U. C. Master Gardeners of Napa County ( http://ucanr.org/ucmgnapa/) are available to answer gardening questions in person or by phone, Monday, Wednesday and Friday, 9 a.m. to Noon, at the U. C. Cooperative Extension office, 1710 Soscol Avenue, Suite 4, Napa, 707-253-4143, or from outside City of Napa toll-free at 877-279-3065. Or e-mail your garden questions by following the guidelines on our web site. Click on Napa, then on Have Garden Questions? Find us on Facebook under UC Master Gardeners of Napa County.