Outdoor cannabis flowering month
Most outdoor cannabis plants in the United States start flowering between late July and mid-August. Harvest follows 8 to 11 weeks later, from late September to late October. Latitude, cultivar, and light pollution move those dates.
cannabis flowering stage yellow leaves
Why flowering starts when it does
Cannabis is a short-day plant. The plant measures the length of the dark period. When uninterrupted darkness passes a threshold, growth shifts from stems and leaves to flower clusters.
cannabis flowering nutrients to use
Most cultivars need 10 to 12 hours of darkness to trigger. Some trigger near 9 hours. Autoflowering cultivars ignore day length and flower 2 to 4 weeks after sprouting.
Dates by latitude
Night length grows after the June solstice. The change is steep at high latitudes and slow near the equator.
When Do Trichomes Appear in Flowering Cannabis Plants?
- 40 degrees north: day length drops below 14 hours in the first week of August. Flowering onset follows within 1 to 3 weeks.
- 45 to 50 degrees north: onset ranges from mid-July to late August depending on the cultivar. The first fall frost ends the season in many of these states in October.
- Below 30 degrees north: the longest day is about 13 hours 45 minutes. Night length stays near 10 hours all summer. Onset dates vary by cultivar.
- Southern hemisphere: the same shift happens in February and March. Harvest falls in April and May.
What delays flowering
Light at night keeps a plant in vegetative growth. Porch lamps, streetlights, and security lights within 10 to 20 feet of a plant can delay onset by weeks or stop it. The dark period must be continuous.
Harvest window
Count weeks from the first flower clusters. Short-flowering cultivars finish in 7 to 9 weeks. Long-flowering sativas take 10 to 12 weeks or more. Late-finishing plants in wet climates carry mold risk in October.
Signs of ripeness: pistils darken and curl in, and trichomes on calyxes turn cloudy, then amber. Growers in rainy regions often cut at cloudy trichomes to beat the weather.
Autoflowering cultivars
Autoflowers carry ruderalis genetics. They flower by age, not by light. A seed planted in May finishes in July or August. Two or three crops fit in one outdoor season in most US climates.