Bernard McMahon or M'Mahon (Ireland ca 1775 — Philadelphia, 18 September 1816) was an Irish-American horticulturist settled in Philadelphia, who served as one of the stewards of the plant collections from the Lewis and Clark Expedition and was the author of The American Gardener's Calendar: Adapted to the Climates and Seasons of the United States (1806 and following years). He circulated the first extensive gardener's seed list in the United States, which he attached as an appendix to his Calendar.McMahon's most enduring contribution was his Calendar, the most comprehensive gardening book published in the United States in the first half of the nineteenth century. It finished in its eleventh edition in 1857. It was modeled on a traditional English formula, of month-by-month instructions on