Frost-Free Days

Frost-free days is the most practical climate metric for outdoor cannabis cultivation, providing a direct measurement of how long the growing season extends in any given location. Definition: the period between the average date of the last spring frost (when overnight temperatures are last below 32°F / 0°C) and the average date of the first fall frost (when overnight temperatures first drop below 32°F again in autumn). Frost is critical because cannabis is highly sensitive to freezing temperatures — a single hard frost can destroy mature flowering plants, killing terpenes and pistil tissue, and can damage vegetative plants severely. Frost-free days by region: Northern Maine, Minnesota, Montana — 90-110 frost-free days (autoflowers required); Central New England, Great Lakes, Iowa — 130-150 frost-free days (fast photoperiods or autoflowers); Mid-Atlantic, Ohio Valley, Kansas — 160-180 frost-free days (most photoperiod hybrids work); Southern California, Florida, South Texas — 250-365 frost-free days (any strain works including full-cycle sativas). Strain selection by frost-free days: 90-110 days — autoflowers only (Royal Critical Auto, Auto Blueberry, Auto Northern Lights — 9-week total cycles); 110-130 days — fast autoflowers + early photoperiods (Early Skunk, Quick One, fastest autoflowers); 130-150 days — most autoflowers + early-flowering photoperiods (Critical Mass, fast OG hybrids); 150-180 days — most modern indica-dominant photoperiods (Northern Lights, Bubba Kush, OG Kush family); 180+ days — sativa-dominant hybrids and slow-finishing strains (Sour Diesel, Haze hybrids, Durban Poison family); 220+ days — pure sativas and equatorial landraces (Acapulco Gold, Thai Stick, Malawi Gold). Look up your local frost dates from USDA Hardiness Zone tables or local extension offices, then select strains with flowering time + germination time fitting within your frost-free window. Royal King Seeds product pages include flowering time information critical for outdoor matching. Hedge against late-season frost risk by harvesting at first amber trichomes rather than waiting for full ripeness, or by extending the season with hoop houses or low tunnels for the final 1-2 weeks of flowering.