How you have to cut your robinia depends on whether it is an original form or a refined variant. There is often confusion between the terms robinia, spherical locust and false acacia. Once you understand the growth of these ornamental shrubs, pruning is uncomplicated.
As the name suggests, the spherical robinia is often grown into a spherical shape
growth
There are two forms of mock acacia commonly planted in gardens. These include the black locust (Robinia pseudoacacia), which is also known as false acacia because of the shape of its leaves, and the spherical locust (Robinia pseudoacacia umbraculifera). This ornamental tree represents a subspecies.
What's the difference?
False acacias naturally develop a short trunk that branches out at low altitude. Spherical locusts naturally form a spherical crown. These small trees grow two meters high and reach a width of four to five meters. Since they do not develop thorns, pruning is not a problem. Most specimens are grafted cultivars that have been grafted onto a standard.
techniques
Neither spherical locust nor false acacia require annual pruning. Nevertheless, both trees prove to be very well tolerated by pruning. Such interventions promote the formation of a symmetrical crown in spherical acacias. You can tell whether the specimen has been grafted by a slight thickening on the trunk. You can completely remove all shoots below this point. If you want to raise the false acacia to a high trunk, you should limb it regularly.
tips
The ideal period for pruning extends from late winter to spring just before the leaves sprout.
thinning
You can thin out spherical acacias generously if the crown has grown too dense. This measure ensures that more light reaches the interior of the crown and no bald spots appear. Remove damaged branches completely by cutting them off at the base above the branch ring. If healthy knots interfere with the symmetry, those are removed as well.
health maintenance
If spherical acacias show damage in the outer crown area, you should shorten them by two thirds. Cut back any acacia branches to keep a dormant eye. This promotes an even appearance, because the wood will sprout in these places in the coming spring.
Even with the false acacia, removing branches is not a problem if they are damaged or grow crosswise and disturb the overall picture. Be careful not to leave any stubs on the root branch when you cut and that the tissue on the branch below remains intact.
radical cut
Radical interventions are advisable in spherical cultivation when the crown shows severe damage. Such measures carry a certain risk that the tree will die. Storm damage or a massive pest infestation can also make a radical cut necessary for false acacias. This original species has a strong tendency to form offshoots after such interventions. In any case, proceed with caution.
How to proceed:
- remove competing branches
- remove specimens that are too close together
- Cut off branches with damaged bark and cracks