Q.When is the best time to prune a Meyer lemon tree that is planted outside and should they be covered when the temperature goes below freezing? A. First of all, citrus does not require a lot of pruning unlike some other fruit trees. You would focus on removing crossed branches, broken branches or branches too close together. Generally speaking, prune citrus right after you harvest the fruit. Myers lemon may begin flowering in January or February and that becomes a bit late because the fruit will not finish until December of the same year, 10 months later. Flowers of Myers lemon This is why it is important to remove the fruit on Myers lemon by the end of December or it may interfere with flowering the following January or February. Growing citrus in our climate is always risky because of winter freezing temperatures. With most cold sensitive plants we would want to wait until after the last possible freezing event. This would put it into perhaps mid-February. Immature fruit of Myers lemon in container Waiting this long, even though it’s the right thing to do with winter tender plants, is a problem with Myers lemon because it begins to flower so early. So we have to take our chances and prune right after harvesting in early January before flowering begins.   This table taken from University of California Riverside document below Frost damage information can be found here Myers lemon should handle temperatures down to about 20° F. The amount of damage depends on the temperature but also on the length of time the temperature remains. So 20° F just before sunrise is a lot less damaging than reaching 20° F at 3 AM and staying there until sunrise.  Immature fruit of Myers lemon in container The number one reason we have fruit failure in Myers lemon in our Las Vegas climate is because of late freezing weather. Even though Myers lemon can withstand temperatures close to 20° F, the flowers or young fruit cannot. They begin to bloom in January or February and may have flowers or very small fruit on the tree and a light freeze comes by and ruins the crop. Then I get emails about why my lemon tree didn’t produce any fruit this past year or last two years.  It is extremely important to put citrus in warm microclimates in Las Vegas yards and out of the wind in our winter cold climate. You will need to cover Myers lemon whenever temperatures get close to freezing, 32° F, if they have flowers or small fruit. If they do not have flowers or small fruit than they can withstand colder temperatures. Another point worth mentioning is that cold hardiness varies during the winter depending upon the weather. During a normal winter, temperatures slowly but continually drop colder and colder until we hit our winter minimum temperatures. Temperatures stay cold during the deepest part of the winter and then minimum temperatures begin to climb as we approach spring.This past fall was nearly perfect as temperatures, generally speaking, dropped lower and lower at a very slow pace. This gradual drop in temperature was reflected in our nice fall colors which remained for about a month in November and December. We had some nice fall color like this during November and December In Las Vegas due to the gradual drop and fall/winter temperatures Some fall/winter/spring weather is not this nice. Sometimes we can get a sudden drop in temperatures in the fall that can catch normally cold hardy plants off guard. Then we see damage to these plants at temperatures warmer than their minimum temperature. The reverse can happen in the spring when we have very low temperatures, followed by an unexpected early rise in minimum temperatures then followed by a sudden drop to freezing weather. This sudden drop below freezing after a warming spell can damage trees at temperatures above their minimum. Sorry for the long winded answer but cover Myers lemon that has flowers and fruit as soon as you hear temperatures might reach freezing.