Lemons (Citrus limon) are produced on small shrubby trees with fragrant white flowers. They are a tender subtropical species that can grow in U.S. Department of Agriculture plant hardiness zones 9 through 11. Lemons do not require regular pruning to bear fruit, though it may be necessary for other reasons once the tree begins to produce, usually in their second or third year.
Lemons often sprout large thorny branches from the base of the trunk. These "suckers" do not bear fruit and should be pruned off. Also prune off "water sprouts" -- vigorous green sprouts that grow straight up from an interior branch. These types of undesirable growth can occur in trees of any age and have a negative impact on the fruit crop if you do not remove them. Also, low, horizontal branches are prone to breaking under the weight of ripe fruit. Prune these off to avoid breakage, though you can also hold them up with wooden supports.
Function and Appearance
Lemons are ornamental plants, but may need pruning to maintain a pleasing appearance or to fulfill other functions. For example, you can train lemons into a hedge, though fruiting will be substantially less as a result of regular pruning. You can also prune lemon trees to maintain their height for ease of harvest. You can prune off branches that grow across the center of the tree to keep a more open, aesthetically pleasing form.
Prune off any dead or diseased wood immediately. After a hard freeze, for example, there is likely to be damage on the tips of branches. If foliage becomes severely discolored or deformed in any way from pests or disease, prune the tree back to where there is only healthy growth remaining. However, areas that have black mildew on the leaves should stay, as this is common to citrus and can be treated by other means.
When to Prune
The best time to prune lemon trees is after harvesting the fruit in late winter, but before flowering begins in spring. However, lemons often have smaller amounts of fruit throughout the year, so it may be impossible to avoid pruning off fruiting branches. Lemons flower only at the tips of the growing branches, so even if there are not currently flowers or fruit, any pruning of a fruiting branch will temporarily delay the production of lemons on that part of the tree.