Organic Answers Column – March 23, 2022

Mexican Sycamore – Better Than the American Sycamore

Few trees are more dramatic and more beautiful than a healthy American sycamore (Platanus occidentalis). They grow large, are majestic in structure, and have dramatic foliage with striking white bark in the winter. Years ago this tree was one of main street trees planted in new developments. Hindsight shows that it would have been much better if developers had planted native oaks and elms because most of the sycamores are dead now. Some are gone because they were planted too deep in the ground, other because of. Planting too deep and disease are probably related.

Both American and Mexican have beautiful structure and bark

Through the years as a landscape architect, I would have ongoing arguments with some my buddies and fellow designers. I saw that the native sycamores and the similar London plane trees were problematic and just not holding up long term. The culprits seemed to be basically two diseases.

American sycamore in winter

Mexican sycamore

Sycamore anthracnose, Gnomonia leptostyla, is a fungal disease that affects sycamores across the country. It’s rarely deadly but makes the trees unsightly and causes large areas of the canopy to die back. The fungus attacks the buds and twigs, so infected trees often have “witches brooms” on the ends of their branches.

In the American native Sycamore and London plane, leaf scorch is more deadly, and hits in late June or July with olive green discoloration of leaf margins followed by margin death. Affected leaves remain attached and the branch tips are the last to scorch or may not scorch at all. Trees with this issue are slow to leaf out in the spring and develop fewer leaves and smaller leaves than scorch-free trees. This eventually leads to branch dieback and tree death. The solution to it we know now is the Sick Tree Treatment.

Mexican sycamore

Mexican sycamore growing in Houston

There is a better choice, a sycamore that doesn’t have these problems. Mexican sycamore (Plantanus mexicana) is an excellent shade tree that is large and fast-growing. Its large lobed leaves are smooth green on the top and dramatically cottony white to silvery below with dramatic exfoliating white bark in winter. Some might argue that the native tree has all those characteristics and would be right to a degree, but there are other issues. Although native to northeastern Mexico, the Mexican sycamore is well adapted to dry, rocky alkaline soils but also adapts to moist soils. The native American sycamore trees are not as adaptable. Both trees grow in full sun and need a little extra water during the establishment period but the Mexican tree is much less problematic long term – and I recommend it highly.