Disputes, occasionally leading to civil court actions, have been known to arise in these situations, so it is wise to consider the implications before planting that suckering tree. In fact, when purchasing any tree it is best to go to a reputable nursery or garden centre whose staff will be able to answer a range of important questions, including whether or not the tree is likely to sucker or produce invasive roots.
Land holders who already own a suckering tree should not simply cut it down, because the roots, reacting defensively, will usually send up many more suckers.
Poisoning the tree first is essential. It is advisable to seek the services of a professional tree carer/surgeon/lopper to remove the problem tree. People tend to think this is expensive, but having the job done properly may save money in the long run.
Common suckering trees
Schinus terebinthifolius comes from tropical South America, which explains one alternative common name, Brazilian pepper, but not the other, Japanese pepper, which it is often called in Western Australia.
Only female trees produce berries but both female and male trees sucker prolifically, causing problems for the people who own them and for neighbours. When pulled up, a seedling can be recognised by its long tap root, whereas a sucker snaps off carrying an end shaped like a hockey stick.
When broad-leaf pepper grows too big, the owners usually lop it back, but the resultant shock promotes suckering. Any soil disturbance that damages the roots also triggers suckering. However, in broad-leaf pepper, suckering occurs even when there is no obvious damage to the parent.
Aside from the suckers, broad-leaf pepper has other undesirable qualities as a garden tree. The crushed ripe berries are known to cause respiratory difficulties for some people, and contact with sap and resin can cause skin irritation.
Robinia or black locust
Robinia, Robinia pseudoacacia, does not produce suckers in all circumstances and some big, old specimens have never caused problems. However, if the roots are disturbed or damaged, vigorous suckering starts.
The smaller ornamental varieties also produce suckers since they are grafted onto R. pseudoacacia rootstock.
Disturbing the soil around a robinia can cut the roots and stimulate suckers.
Occasionally the results are extreme. For example, if an old house is demolished and the garden containing a robinia is bulldozed, root fragments left in the ground will send up suckers long after the block has been redeveloped. Pulling them up is not easy because the suckers have sharp, sturdy thorns — and, in any case, it is futile since more suckers will emerge in their place.
Other suckering trees
Paulownia, gleditsia, tree of heaven, and a number of other trees can be problematic to varying degrees. Royal paulownia, Paulownia tomentosa, grows rapidly and if the owner decides it is getting too big and cuts it down, suckers are generated. Commercial varieties of gleditsia or honey locust do not have the savage thorns of the species, Gleditsia triacanthos, but the suckers do, which makes them difficult to handle.
Tree of heaven, Ailanthus altissima, suckers so freely that some people suggest it should be called tree from hell. Handling the plant can lead to a rash and other allergic symptoms. Its other unpleasant features are flowers with the odour of rotting meat, leaves which also smell offensive when bruised, and an ability to produce toxins which accumulate in the soil and inhibit the growth of other plants.
Poplars and aspen are no longer widely planted in Western Australia, because their suckering habit is already well known. However, in cooler, damper, southern areas many trees still exist that were planted long ago, often as wind-breaks or feature trees in gardens and paddocks.
The main species are the tall, slender Lombardy poplar, Populus nigra var. italica, white poplar, P. alba, and aspen, P. tremula. All sucker profusely in response to disturbance including mowing, cultivation or trampling by stock. If left unattended, the suckers can form dense thickets.
Old gardens and orchards occasionally contain what are loosely referred to as “wild cherry” or “wild plum” trees. Usually these are cherry-plum, Prunus cerasifera, or other very similar species, any of which can appear to be self-sown.
These small, densely branched trees may grow from seeds spread by birds, or they may arise as suckers. Some ornamental cherry and plum trees have been grafted onto P. cerasifera root-stock. In these cases – as with many other grafted trees – death or disturbance of the grafted portion can trigger the production of suckers. If left to grow, these form a large deciduous shrub or small tree with generally straight, stiff stems that often end with a sharp tip. In turn, these trees or shrubs can produce further suckers.
A “tree and blackberry killer” type of herbicide is the only effective treatment for killing the parent tree. Follow the instructions on the label carefully. Given time, the poison travels to the suckers and, once all are dead, the parent can be felled. Felling any large tree should be left to a tree removal specialist who has the proper equipment and, importantly, the proper insurance cover.
Suckers from a neighbour’s tree
Cutting the suckers off and painting the cut ends with “tree and blackberry killer” herbicide is only a short-term solution if the tree is in a neighbour’s garden. Installing a root barrier may be effective, depending on the depth of the roots. Generally, however, if the parent tree is in a neighbouring garden and the owners refuse to kill it, suckers will be an ongoing problem.