http://www.tracypress.com/view/full_story/5603978/article-The-Green-Thumb--Save-your-citrus?instance=home_our_town

The Green Thumb: Save your citrus

by Heather Hamilton/ Our Town
Jan 19, 2010

When we bought our home, it came with two well-established citrus trees: a lemon and an orange. They are planted next to each other and receive the same water, sun and fertilization. Although both plants are similar, the winter weather affects the trees differently: The orange tree survives unscathed through cold snaps that heavily damage our lemon tree.

Generally speaking, the sweeter the citrus, the more cold-hardy it is likely to be. Mandarins are slightly hardier than oranges, oranges are hardier than grapefruit, grapefruit are hardier than lemons and lemons are hardier than the most sensitive citrus fruit — limes.

The Tracy area has experienced some nighttime temperatures recently that could have damaged lemon and lime trees. If you suspect your tree has suffered frost damage, though, the best thing you can do for it is nothing at all.

We have received enough rain lately that all outdoor, in-ground plants should be well-hydrated. In the Tracy area, we can experience cold overnight temperatures through March, and pruning back any frost-damaged limbs now would open up the tree for even more damage, should the cold temperatures return. You can, however, carefully remove any fruit that feels soft (a sign of cold damage). In April or May, you can begin to prune any damaged branches.

Most orange varieties are cold-hardy to 27 degrees, lemons to 30 degrees, while limes cannot withstand any frost. My family has a genetic dwarf Mexican (or Key) lime that we grow in a large pot, so it can be taken under cover in the winter. We cover it with an old tablecloth when temperatures are predicted to drop below 45 degrees, just to be safe.

If you have a Meyer lemon tree — a milder hybrid of a lemon and either a mandarin or an orange — note that it can withstand colder temperatures than most lemons.

• UC-certified Master Gardeners are available to answer your gardening questions from 9 a.m. to noon Tuesdays, Wednesdays and Thursdays at 953-6112 or mgsanjoaquin@ucdavis.edu. Questions for Heather Hamilton can be submitted to ucmastergardener@gmail.com.