How to determine if potted mandarin regrowth is root stock?

erikc

This potted Japanese mandarin from Bunnings lost all its leaves, I cut it back and repotted it and it grew healthy but small leaves but are they mandarin leaves that aren't branching out due to winter or is this the rootstock taking over? How can I tell?

EricL

Hello @erikc 

Looking closely at your Japanese mandarin, the new flush of growth does appear quite healthy, though there are a few important things to check when working out whether the shoots belong to the grafted mandarin or whether the rootstock has taken over. If you can post a few close-up photos of where the leaves are sprouting from, our members will be able to give you better advice.

Mandarin graft unions are usually quite visible as a slight bulge, scar, or change in bark texture low on the main stem. Any growth that emerges from below the graft line is rootstock, not your desired mandarin variety. From your photos, it looks like the fresh leaves are sprouting from just above where the old wood was cut back. If that point is above the graft union, then the tree is still producing mandarin leaves. If, however, the graft point was cut away or the new shoots are sprouting below it, then what you are seeing is almost certainly rootstock regrowth.

Leaf shape and texture can also be a clue. Mandarin leaves are typically rounded with a slight “wing” on the petiole, whereas many citrus rootstocks, such as trifoliate orange or rough lemon, tend to have more elongated, crinkled, or unusually shaped leaves. In your photos the leaves look fairly typical of a mandarin smooth-edged, glossy, and without the distinctive winged petiole that trifoliate rootstock usually shows. That is encouraging and suggests you still have your mandarin variety rather than just rootstock growth.

At this stage, because it is winter, it is normal for mandarins in pots to show slower growth and reduced branching. They often push small clusters of leaves on short stems until the warmer months arrive, when side branching and more vigorous shoot extension will happen naturally. To help encourage a stronger framework, you can lightly tip prune in early spring once the weather warms, which should stimulate side shoots.

If you need further assistance, please let us know.

Eric