My orange tree above looks fine, right? That’s what I thought until I crouched down and noticed this little devil:
That branch growing from the base of the trunk — that’s the little devil. It’s not a branch of my orange tree; it’s rootstock.
Citrus trees are usually grafted
Almost every citrus tree you buy from a nursery is actually two trees in one. There is a rootstock on the bottom, and there is a scion on top. The scion is the part that gives you the fruit you desire — Washington navel orange, Tango mandarin, Eureka lemon, Oroblanco grapefruit, and so on.
(Why do citrus trees have a rootstock? See my post “Fruit trees are grafted — Why? And so what?”)
(How do they graft citrus trees? See this video of one method used at Four Winds Growers.)
Spotting graft unions
Usually you can spot the union where the rootstock and scion were grafted together because the bark has a change in shape there. Here’s a graft union that looks like a diagonal line:
Here is a graft union that looks like a bump all the way around the trunk:
As a citrus tree gets older, the graft union either almost disappears or it becomes a severe and obvious bump, depending on the kind of rootstock used.
Here is an example of the severe, obvious bump, which citrus people often call a “bench,” on an old Valencia orange tree in my grandparents’ yard:
Beware of branches below the graft union
Beware: If a branch emerges on the trunk from below the graft union, then it is rootstock — often called a rootstock sucker — and it will be vigorous and it will take over the whole tree if you don’t stop it.
Rootstock suckers on citrus trees are indeed little devils, and they often sneak by even the most knowledgeable and attentive gardeners. They can grow even before a tree is planted in your yard. I’ve seen rootstock suckers growing on citrus trees that are still in pots at nurseries.
This is sad because a person might buy such a tree, plant it in their yard, and get some fruit in a couple years that is sour or seedy or ugly and wonder what kind of crazy mutation has occurred: “I bought a blood orange tree, but this fruit never gets bloody or sweet!?”
Also, rootstock suckers can take over old citrus trees. All through my youth, I visited my grandparents’ in the summer and swam in their pool, and beside the pool was a kumquat tree that I snacked on. Just a couple weeks ago, I checked that old kumquat tree to find this:
Can you see the only fruit in there? It looks like a lemon. It’s not; it’s rootstock fruit. Rootstock had taken over the entire tree, somehow, and neither my grandparents nor I had noticed.
Signs that a branch is rootstock
But notice this:
It’s never a good sign when a citrus tree has multiple trunks. Almost always when I see a citrus tree with multiple trunks, I find that it is all rootstock, or there might be a single trunk in the middle that is barely still alive that is the scion variety. Here on my grandparents’ kumquat it is all rootstock.
Other warning signs that branches are rootstock — besides the branches bearing the “wrong” kind of fruit and there being multiple trunks — include very thorny branches. Rootstock branches are usually very thorny whereas the branches of the scion variety are usually not very thorny or the thorns are small. (Do note that I say usually. If you have a Yuzu tree, you know what I mean.)
Finally, a sure giveaway that a branch is rootstock is if it has leaves in clusters of three.
A common rootstock used for many citrus trees is a type of “trifoliate” or three-leaved citrus, for example the C-35 citrange. But no scion variety that we plant has leaves in clusters of three like this.
In 2013, I moved into a house with numerous old citrus trees in the yard. A few were healthy, most were not. As I watered some to try to revive them I got a lot of new growth, but not all of the new growth was desirable: much of what was still alive was rootstock. Here’s one old tree that I no longer water yet survives on winter rainfall in Southern California:
Multiple trunks, thorny branches, unfamiliar and sour fruit. It’s all rootstock. You can see that the scion variety at the top has long ago died.
Don’t let this happen to your citrus tree. Check for rootstock suckers often, and as soon as you notice one snap it off or cut it off close to the trunk or ground.
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