Lemon trees, like many members of the Citrus genus, naturally possess thorns, which are modified stems that develop from the axillary buds of the branches. The presence of these sharp structures is common across various lemon varieties, and their size and abundance can vary depending on the specific cultivar. This characteristic is not a sign of a problem, but rather a feature that has been selectively bred out of some commercial varieties for ease of harvest.
The Biological Purpose of Citrus Thorns
Citrus thorns serve primarily as a defense mechanism, offering physical protection against herbivores. These pointed structures deter animals, such as grazing mammals, from eating the plant’s leaves and young, tender shoots. This protection is especially helpful when the tree is young and its growth is more vulnerable to damage. The plant invests energy into producing these thorns to ensure its survival and ability to reach maturity. Thorns help to guard the tree’s biomass until it is large enough to withstand some browsing.
Identifying Common Thorny Lemon Varieties
Many common lemon varieties are known for their significant thorn production. The ‘Lisbon’ lemon is perhaps the most vigorous and thorny of the commercially grown types, with sharp, rigid thorns that can be quite large. These thorns are often found on young growth and can persist throughout the tree’s life. Another type with notable thorns is the ‘Rough Lemon,’ which is frequently used as a rootstock for other citrus trees. While its fruit is often considered inferior, the tree itself is exceptionally thorny and robust. In contrast, the ‘Eureka’ lemon is widely favored in commercial production because its canopy is more open and it has fewer thorns. The ‘Meyer’ lemon, a hybrid, is also known for being compact and generally thornless, making it a popular choice for home gardeners.
Thorns and Tree Maturity: Rootstock Implications
A common observation is that a lemon tree’s thorniness often decreases as it transitions from juvenile to mature growth. Young trees produce more thorns on their stems, but as the branches age and harden, the number of new thorns tends to diminish, or they become smaller and less rigid. This change reflects a reduced need for intense physical defense once the tree is established.
Most lemon trees bought from a nursery are grafted, meaning the desired fruiting variety, called the scion, is attached to a separate, hardy root system, the rootstock. Thorns are frequently a sign that a branch is emerging from the rootstock, which is typically a more vigorous and thorny variety like ‘Rough Lemon’ or trifoliate orange. These rootstock suckers grow from below the graft union, and they often display large, numerous thorns that are much more aggressive than those on the upper, fruiting part of the tree. Identifying the graft union, usually a slight change or bump on the lower trunk, is important to distinguish between the fruit-producing scion and the rootstock. Any thorny, vigorous shoots that sprout from the trunk below this line should be pruned away completely. If left to grow, these thorny rootstock branches will divert energy from the desired lemon variety and producing inferior or unpalatable fruit.