Imagined as accessible and portable guides to the kitchen garden, eighteenth-century garden books in the form of encyclopedias, almanacs, and calendars circulated around the Atlantic World attempting to teach gardeners in disparate regions how to interpret and transform their local environments. However, as the horticulturalists were quick to argue, no matter where the garden was located, the key to good gardening was timing: planting, grafting, weeding, and harvesting all depended on the gardener’s sense of time and knowledge of place. Encompassing garden books from the 1680s to the 1820s, and published in England, Scotland, Ireland, and the nascent United States, this article argues that gardening calendars, encyclopedias, and almanacs both in format and content composed a running debate among professional garden authors over how best to represent time on the pages of a book. During this period, scientifically minded practical gardeners wrote against mechanical and regularized time and proposed different methods for finding a more accurate and more universal organic timekeeper. The ideas they proposed, and the solutions they found, did not consciously aim for something called “modern time.” However, their proposals did emphasize the need for portability, universal application, mobility, and standardization in timekeeping technology—all features associated with modern timekeeping. In this transnational environmental history of timekeeping practices, I argue that focusing too heavily on clocks has prevented historians from understanding the myriad other technologies—like the format of a garden calendar or the practice of growing melons in a box of dung—that also contributed to the systematization and standardization of timekeeping in the long eighteenth century.