We’re looking at buying more citrus trees, but we’re wondering which ones have thorns. I looked it up online, but there’s not much information out there. So, I did some research to find out more. Here’s what I found about citrus trees and thorns.
The majority of citrus trees have thorns as they were made to defend the trees against browsing herbivores and to retain water. Only a few varieties such as Eureka lemon and Persian lime were bred to have little to no thorns. Citrus tree thorns aren’t poisonous and don’t need to be removed.
So, why do citrus trees have thorns in the first place, and exactly which ones have them? Let’s take a closer look.
Which Citrus Trees Have Thorns?
| Thorny Citrus Trees | Thornless* Citrus Trees |
|---|---|
| Mandarin Orange | Eureka Lemon |
| Navel Orange | Persian Lime (Tahiti Lime) |
| Blood Orange | Fallglo Tangerine |
| Meyer Lemon | Dancy Tangerine |
| Lisbon Lemon | Bearss Lemon |
| Key Lime | Meiwa Kumquat |
| Mexican Lime | |
| Kaffir Lime | |
| Tangerine | |
| Tangelo | |
| Grapefruit | |
| Kumquat |
Many gardeners prefer to plant thornless citrus trees to avoid getting their fingers pricked, but this can’t always be avoided.
Generally, it’s rare for a citrus tree to be truly thornless as the trees have developed them over many tens of thousands of years.
Why Do Citrus Trees Have Thorns?
Just as starfish, thorny dragon lizards, and hedgehogs are covered in spikes and quills to deter predators, citrus trees grow thorns to protect their fruit and leaves from the mouths of browsing herbivores.
Thorns also retain water to some degree. They do this by trapping moisture and dripping around the base of the plant as a slow, constant source of water.
Most of today’s citrus trees did not originate in the wild but are the result of centuries of plant breeding.
For example, lemons began as an intentional cross between citron (an ancient tree, still around today, that’s almost all rind and no juice), pomelo (the thick-rinded grapefruit ancestor), and mandarin (the ancestor to most hybrid citrus today).
Because all three of these parent species evolved with thorns, they gave this prickly trait to the lemon tree.
Citrus trees create thorns by modifying stem cells in branches to end at a sharp point.
Young citrus trees produce the most thorns as they need the most protection from herbivores. This helps them grow to maturity and bear seedy fruit to make the next generation of trees.
Once the trees reach maturity, they produce fewer thorns since most of their branches are safely out of reach of herbivores.
Should Citrus Tree Thorns Be Removed?
Removing thorns from citrus trees largely comes down to 3 factors.
- Scratching
- Protection and Water for the Citrus Tree
- Fruit Disease
Citrus tree thorns can scratch gardeners when handling the plant or harvesting fruit. Because of this, you can remove the thorns if desired. Removing the thorns minimizes scratching and makes it easier to care for the trees.
Another reason to keep the thorns is to maintain the tree’s ability to harvest extra water. The thorns help the tree tolerate drought better through a slow drip of water off the branches. If you live in a dry area such as California or Arizona, leaving the thorns is likely a good idea.
Additionally, citrus tree thorns can puncture the growing fruit which provides an entry point for a bacterial disease called Citrus Blast (Pseudomonas syringae). Citrus Blast causes the tree’s leaves and twigs to die and fruit to develop black spots. Removing the thorns helps prevent this condition.
Pruning citrus thorns is harmless to the tree. As long as you use clean, sharp shears, your tree will recover quickly.
However, if your citrus trees are grown in an area that’s often browsed by deer or other hungry herbivores, consider keeping the thorns for the tree’s protection.
In the end, the decision to prune the thorns is a personal one. If you decide to remove them, wear long sleeves and thick leather gloves. Hold the limb in one hand, start pruning from the base, and snip each thorn to where it meets the branch.
Are Citrus Tree Thorns Poisonous?
Although the thorns on citrus trees aren’t poisonous, the oil from the leaves is known to occasionally cause irritation. You should still be careful around the thorns to avoid scratches. From the dirt and plant matter in your garden, infection is possible.
Do Citrus Trees With Thorns Produce Fruit?
Thorns do not reduce fruit growth on citrus trees. You’ll often find the thorns on the same branches that are also holding fruit.
All citrus trees, regardless of how many thorns they may have, produce fruit provided they are planted (or potted) in an ideal location and are given what they require for healthy growth and fruit production.
However, citrus trees grow thorny suckers, or side shoots, at a 90º angle (out of the “armpit” of where the branches meet the trunk). These thorny suckers require excess water and nutrients to grow, reducing the citrus tree’s fruit and foliage.
Pruning thorny suckers as well as excess branches encourages the citrus tree to focus on growth.
When to Prune Citrus Trees
For young citrus trees (under 3 years), prune any clusters of flowers or fruit to encourage the tree to reach a mature canopy sooner. Once citrus trees are mature, prune redundant and overlapping branches to promote airflow, sunlight, and higher-density fruiting.
Take care not to over-prune as it can impact the tree’s ability to photosynthesize and provide good yields.
If you bought your citrus tree from a nursery, it’s likely not grown by seed, but a graft of two different trees. When you look at your citrus tree, look down toward the base and you can often see the junction or scar where a graft took place.
Below the graft, thorny suckers from the original rootstock commonly sprout and grow wild, quickly taking over the tree and making it harder and more painful to access.
Whether they come from the rootstock or the canopy, you can identify suckers because they are thin, tall, and shoot up quickly. Remove them in spring or whenever you see them.
To learn more about suckers, pruning, and grafting, check out this video by IV Organics.
The Best Way To Fertilize Citrus Trees
Citrus trees prefer double the nitrogen to other ingredients. This means an NPK (nitrogen, phosphorus, and potassium) ratio of 2:1:1, such as a 6-3-3.
If you’d like my recommendation for citrus tree fertilizer, check out my recommended fertilizer page.
