For example, fruiting cherry trees are actually composed of two different types of cherry trees. The ‘understock’ below the graft is provided by a cherry tree that develops good roots, but that may not make very good fruit. The ‘scion’ above the graft is provided by a cherry tree that develops desirable fruit, but that may not be able to develop a healthy or otherwise desirable root system.

 

A graft union can be found just above the ground, with different bark textures above and below the graft. The smooth light gray bark of English walnut is particularly different from the dark furrowed bark of its black walnut understock. The trunks of young trees are often slightly kinked at their graft unions.

 

Suckers are shoots that develop below a graft union. If not removed, suckers can intermingle, compete with, and eventually overwhelm the desirable plant parts that are above the graft. 

Weeping flowering cherry trees are actually composed of three genetically distinct trees. The understock provides the roots. A mediary scion provides the straight, vertical trunk. The upper scion provides the weeping branches with showy bloom. Therefore suckers from below a graft can come either from the roots, or from the main trunk just below the canopy. Because the weeping upper scion does not grow as aggressively as upright suckers from the trunk or roots, it can easily become overwhelmed.

Roses, citrus, apples, pears, and all sorts of fruit trees (and their fruitless, ‘flowering’ counterparts) are susceptible to suckers. Those that grow slowly are more susceptible than those that grow more vigorously are. Consequently, a typically slow growing Mexican lime is much more likely to be overwhelmed by suckers than a typically vigorous Lisbon lemon, even though both are grafted onto the same understock.

Suckers should be removed as soon as they are observed. It is actually best to peel them off than to prune them off if possible. Peeling seems to be more damaging, but removes more of the undifferentiated ‘callus’ growth that develops suckers. Pruning leaves a wound that is more likely to produce more suckers again later. Of course, large suckers will need to be pruned off if peeling would be too damaging.

Sadly, by the time a weeping flowering cherry has become an upright tree, it likely is not salvageable. The suckers are the predominant part of the tree, and may have even shaded out and killed all of the weeping upper scion. Even if part of the upper scion remains, trying to prevent secondary suckers from developing from where large suckers have been pruned away may be futile. If the suckers bloom well, they can be left as an upright flowering cherry tree. It would otherwise be more practical to replace such a tree.