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Lemon trees are a variety of plant that is actually more accurately described as a shrub. While some homeowners enjoy trimming their lemon trees to give them a more tree-like appearance, such trimming will actually reduce the amount and quality of fruit production. In states such as Arizona, where citrus is farmed and exported, the plants are permitted to freely grow into enormous overgrown shrubs, and only trimmed when absolutely necessary. According to John Begeman, a professor in the College of Agriculture and Life Sciences at the University of Arizona, the optimal time for trimming lemon trees is mid-November to ensure the tree's stalk will not become sunburned.
Inspect the tree for sucker branches. These branches grow below the point where the tree was grafted and will not produce edible fruit. Remove these branches with pruning blades close to the trunk. whenever discovered to avoid the risk of the entire tree being taken over.
Inspect the tree for errant branches. Errant branches are those that are growing in either the wrong direction and intercepting another branch or pressing against a building. Trim as few stalks as possible from these branches, and only what is necessary to correct the growth.
Trim away any branches that make it difficult to fertilize the plant. Trim the branches completely back to the stalk, as they will most likely not produce fruit after being trimmed and will ideally not re-grow.
Allow the tree to heal itself from the trimming.
If trimming in spring to remove sucker or errant branches, whitewash the trimmed area to protect the tree's trunk. To create the whitewash, mix together one part white latex paint and nine parts water and brush the mixture over the trimmed area. Whitewashing will prevent the trunk from getting burnt.