Citrus trees are evergreen perennials and have a cold hardiness range of 25 to 30 degrees, depending on the type of citrus planted. The San Joaquin Valley’s climate is almost ideal for growing citrus, with hot, dry summers and cold, mild winters.
There is an astounding variety of citrus available to the home gardener, in many varieties: sweet and sour oranges, grapefruits, lemons, limes, pummelos, mandarins, tangelos, kumquats, kumquat hybrids and citrons.
The best time to plant citrus trees is during the spring, after the danger of frost is past.
Choose a good site for your citrus tree. South-facing sites with reflected heat from a wall are the best, with a west-facing site the next most desirable. Avoid low spots where cold air can accumulate in winter. Planting in a raised bed can help citrus trees in cold weather, as the cold air flows downward and away from the trees. If space is tight, espalier the tree against a south-facing wall.
Keep in mind that a mature standard sized tree can grow 20 to 30 feet tall and as wide. Dwarf trees are about a third smaller.
Don’t plant citrus trees near other plants with aggressive root systems, so that they don’t compete for water and nutrients.
When planting your citrus tree, dig a hole as deep as the container and twice as wide. Gently remove the tree from the container. Citrus roots are delicate and tend to be shallowly rooted. The top of the root ball should be about 1 inch above the surrounding soil.
Backfill the hole, leaving the top of the root ball exposed about a quarter inch. Water the tree thoroughly to eliminate air pockets, and keep roots moist until they’re able to grow into the surrounding soil. The roots will die if they dry out.
Whitewash the trunk with a mixture of 50 percent exterior latex paint mixed with water to avoid sunburn.
Citrus trees should be fertilized or pruned after the last spring frost, stopping in late summer, because tender new growth is more susceptible to damage from cold and wind. Pruning stimulates new growth.
Citrus trees have a general tolerance to cold down to about 30 degrees. Temperatures below 30 may result in leaf, fruit and branch damage.
The range of citrus cold-hardiness, from least to most cold-hardy, is: citron, lime, lemon, grapefruit, pummelo, tangelo, tangor, limequat, sweet orange, mandarin, Meyer lemon, sour orange, orangequat and kumquat.
If frost is predicted, water the tree one or two days before and again after the freeze; wrap the trunk with burlap or some other insulating material; hang outdoor Christmas lights on the tree; and build a tent around the tree, not allowing the branches or leaves to touch the tent walls, because they will be damaged if they do.
If you take care of your citrus trees, they will reward you with beauty and fruit for many years.
• The Green Thumb is a column by Tracy’s master gardeners. University of California-certified master gardeners are available to answer gardening questions from 9 a.m. to noon Tuesdays, Wednesdays and Thursdays at 953-6112 or firstname.lastname@example.org.