Globe trees, such as the Globe Maple and Globe Robinia, are a popular choice for gardens, particularly in front yards where they create beautiful tree portals over time. However, to maintain their attractive rounded shape, it’s essential to prune them properly.
What Makes Globe Trees Special?
Unlike standard tree species, globe trees naturally grow in a compact, rounded shape due to a genetic mutation. This mutation causes the terminal bud (at the tip of each branch) to produce less growth than the side buds, resulting in a spherical crown instead of the typical oval shape that develops in wild tree varieties. To achieve a straight trunk, gardeners often use a wild-type rootstock and graft the globe variety at the desired height for the crown.
Among the most popular globe trees are the Globe Maple (Acer platanoides ‘Globosum’) and Globe Robinia (Robinia pseudoacacia), as well as the Globe Catalpa (Catalpa bignonioides ‘Nana’). The Globe Cherry (Prunus fruticosa ‘Globosa’) is another option, though it’s increasingly rare due to its susceptibility to tip blight.
Pruning Globe Trees for a Compact Shape
While globe trees are generally smaller in height, they can spread significantly with age—something many gardeners overlook. To maintain a compact, globe-like crown, pruning is required every few years. This regular cutting helps control the tree’s shape and size.
Best Time for Pruning
The late winter months, before the new growth begins, are ideal for pruning. During this time, you can trim the main branches back to about 15 to 20 centimeters. Use a sharp pruning saw or secateurs, and be sure to make clean cuts just above a dormant bud, which will allow for new growth.
It used to be common practice to seal pruning wounds with tree wax to prevent infection, but this is now discouraged. Studies show that sealing cuts can trap moisture and encourage fungal infections, so it’s best to leave cuts exposed to air.
How to Prune
- First Pruning: After planting, cut back branches to the desired shape, removing the strongest shoots. This creates a clean, compact crown.
- Subsequent Prunings: After 3-4 years, you may need to prune again, but this time, only trim the new growth that has emerged from the initial cuts. Avoid cutting too far back and instead reduce the number of new shoots if the crown is too dense.
Special Considerations for Globe Maples
While most globe trees tolerate pruning well, the Globe Maple (Acer platanoides ‘Globosum’) requires special attention. These trees tend to bleed heavily when pruned in the spring, as they release sap from the cut areas. While this isn’t harmful to the tree, it can look unsightly. For Globe Maples, it’s best to prune in late summer or early autumn, and avoid cutting branches thicker than a finger.
Maintaining the Globe Shape
The key to keeping your globe tree attractive is regular pruning. By following these guidelines, your tree will remain healthy, compact, and a stunning feature of your garden for years to come. Regular maintenance is especially important as globe trees mature and their natural growth tendencies begin to expand.