With the onset of winter comes the cold. Depending on where you live you may have begun watching the weather reports to get ahead of a cold snap that could damage your Citrus or Avocado plants.
Depending on the variety, a rule of thumb is Citrus and hardier Mexican varieties of Avocados will tolerate to 30 degrees Fahrenheit for about 3 hours without damage. Some noted exceptions would be the Mexican Lime and any citrus or Avocado tree that has been recently planted.
Selecting the best location to plant is your best advantage against the cold. Choose locations that have good air movement but not exposed to high winds and avoid low locations where cold collects during the fall and Winter. In marginal citrus locations (zone 7) selecting a wall of the house or a south facing wall that radiates heat to add protect to your plants. Avocados are not recommended for planting in the ground in Zone 7.
Protection for you citrus should begin in the late summer. A good feeding with and organic fertilizer in September will help add to the protection against winter frost. The current rule is a well fed and well-watered citrus will improve the plants tolerance to cold. Also with Zone 7 Citrus, colder weather may call for wrapping the trunk into the lower canopy with burlap or old blankets and then mulching the base of the tree to 4 inches out past the canopy adds to the overall protection
In all zones prone to freezes a frost blanket to cover the tree is essential. Adding 100 watt conventional bulb or a string or 2 of C9 Christmas lights hung through the trees under the Cover will add to the degrees of captured heat. I have found that during the cold periods leaving the covers on for a few weeks will not bother the tree. Be sure to turn the lights on early in the evening to allow the heat to collect under the cover. There is some evidence that pulling back the mulch during the warm part if the day allows the ground to heat up to be released into the canopy later that evening.
The real trick to successful Citrus and Avocado Protection is keeping the trees below 10 feet during the growing season. I recommend below 8 feet to make covering and adding protection like lights a breeze. When size control is a part of your Citrus and Avocado growing adding a simple structure around your tree is easy and makes applying a frost blanket simple.
Applications of any of the Anti-transparent products are not recommended. Any damage that might occur on the trees as a result of winter cold should be left until the temperatures begin to stabilize in the spring to be pruned off.
Finally, selection of varieties can mean the difference between success and failure. Very few avocados that are not of the Mexican type will survive in a winter cold climate such as Zone 8 or 9b or lower.
Varieties like the Mexicola, Fuerte, Stewart, Jim Bacon, and Zutano are good to try. The all popular commercial Hass should be reserved for Zone 9a and greater.
For the hardest of the citrus, the varieties that are able to tolerate to 28 degrees for short periods are the Meyer Lemon the hardiest of the lemons, Kumquats with Nagami being the most well-known and the Fukushu a newer very sweet large fruited tree gaining in popularity. Calamondins are a very cold hardy kumquat like fruit used mostly in cooking. Owari Satsurma mandarin is a noted cold hardy variety and are very dependable. The jury is still out on newer varieties like Gold Nugget and Pixie. The Yuzu a fruit used primarily for Asian cooking is thought to be the hardiest of all the citrus. Sweet Oranges must be protected along with most Lemons, Limes and Grapefruit. Some varieties to try in these zones are the Trovita Orange, Lisbon Lemon, Bears or Persian Lime and the Oro Blanco Grapefruit.
For all other varieties grown in Zone 9a, 10 or higher, simple recommendations for covering your plants and feeding and keeping them watered in the event of a hard freeze are the order.