Answer: Sycamores (Platanus occidentalis) are very large trees, one of the largest native to our area. You might see them as tall as 150 feet in the wild, certainly to 100 feet when planted. Their growth rate is medium, maybe two feet a year, and they grow best in deep, rich soils with ample moisture. According to Michael Dirr's "Manual of Woody Landscape Plants" the seeds should not require any pretreatment to germinate, although several months of cold treatment might be beneficial. You might try planting some now and some in very early spring, much as they would be when done by nature. You should keep in mind though that these trees grow so large and also tend to drop bark, branches and seeds all over and so are not considered optimal for small scale residential plantings.
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