Graft citrus frees in either fall or spring. Whip grafting is used for small trees and bark grafting for large trees. As the UC Extension notes, trees grafted in the fall should be given protection from freezing weather.
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Marie Notnats enjoys learning about new topics and teaching people new skills. She has been writing professionally since 2008. She is a professional horticulturist with a Bachelor of Science degree in horticulture from Brigham Young University. She writes for About.com, Examiner.com, eHow, and assorted gardening blogs.