The optimal period for introducing onion sets or transplants into the ground within USDA plant hardiness zone 5 is dictated by both soil temperature and the length of daylight hours. Successfully cultivating onions requires careful consideration of these regional and temporal factors to ensure proper bulb development.
Timing is paramount for a successful harvest. Introducing onion plants too early subjects them to potential frost damage, while planting too late may not provide sufficient time for the bulbs to mature fully before the end of the growing season. Historically, farmers and gardeners have relied on observing local environmental cues, such as the last expected frost date and soil warmth, to determine the appropriate planting time.