Colorado Outdoor Cannabis Grow Calendar
When to germinate, transplant, flower, and harvest outdoors in Colorado — based on local frost dates and climate.
Key Dates at a Glance
Germinate seeds
April
indoors
Transplant outdoors
June
after last frost
Flowering begins
August
photoperiod strains
Harvest
August
before first frost
USDA Zone
USDA Zones 3-7
Outdoor season: Indoor only (state law)
Outdoor Viability
Indoor growing strongly recommended
Colorado legal limit: 6 plants per person under Amendment 64 (Colorado Marijuana Legalization). Plants must be out of public view.
Full Colorado legal guide →About Growing Outdoors in Colorado
While Colorado has excellent sunshine and low humidity ideal for cannabis, state law requires indoor cultivation. The high altitude (5,000-10,000+ ft) means intense UV rays but also challenges: faster water evaporation, lower air pressure affecting plant metabolism, and extreme temperature swings. LEDs work great at altitude.
Month-by-Month Schedule
- ●Order seeds from a reputable seed bank
- ●Plan your grow space and check for any local ordinances
- ●Order seeds from a reputable seed bank
- ●Plan your grow space and check for any local ordinances
- ●Order seeds from a reputable seed bank
- ●Plan your grow space and check for any local ordinances
- ●Prepare soil amendments, pots, and growing supplies
- ●Germinate seeds (paper towel method or directly in soil)
- ●Keep under a CFL or small LED on a sunny windowsill
- ●Maintain warm temps (70-80°F) and high humidity (65-70%)
- ●Transplant seedlings into 1-gallon pots once they have 3-4 sets of leaves
- ●Begin gentle hardening off — short daily exposure to outdoor conditions
- ●Monitor for pests and damping off
- ●Last frost typically ends: Mid May - Early June
- ●Transplant outdoors AFTER your local last frost date
- ●Use 5–10 gallon fabric pots or direct-in-ground for bigger yields
- ●Protect young plants from strong winds for the first 1-2 weeks
- ●Plants enter flower as daylight drops below ~14 hours
- ●Switch to bloom nutrients (lower N, higher P/K)
- ●Stake or trellis heavy branches — buds get dense and top-heavy
- ●Watch humidity — drop RH below 50% if possible to prevent bud rot
- ●First frost typically starts: Late September - Mid October
- ●Harvest BEFORE first frost — frost damages buds
- ●Check trichomes with a jeweler's loupe — cloudy = peak THC
- ●Flush 1-2 weeks before harvest (plain water only)
- ●Dry in a dark, cool (60-70°F), ventilated space for 7-14 days
- ●Cure buds in glass jars — burp daily for first 2 weeks
- ●Minimum 2-4 weeks cure for quality; 6-8 weeks is ideal
- ●Review notes from this season, order seeds for next year
- ●Cure buds in glass jars — burp daily for first 2 weeks
- ●Minimum 2-4 weeks cure for quality; 6-8 weeks is ideal
- ●Review notes from this season, order seeds for next year
- ●Cure buds in glass jars — burp daily for first 2 weeks
- ●Minimum 2-4 weeks cure for quality; 6-8 weeks is ideal
- ●Review notes from this season, order seeds for next year
- ●Cure buds in glass jars — burp daily for first 2 weeks
- ●Minimum 2-4 weeks cure for quality; 6-8 weeks is ideal
- ●Review notes from this season, order seeds for next year
Best Outdoor Strains for Colorado
Strain selection matters more outdoors than indoors. Pick a variety matched to Colorado's climate and season length.
Pro Tips for Colorado Outdoor Grows
Autoflowers are forgiving
Autoflowers finish in 8-12 weeks regardless of light cycle. In Colorado's shorter outdoor window, this is often the safest choice for beginners.
Watch the last frost
Transplant AFTER Mid May - Early June. A single frost night can kill young plants. When in doubt, wait another week.
Cover if a cold snap comes
Keep row covers or a portable greenhouse ready if your forecast shows unexpected cold nights in early or late season.
Harvest before first frost
Your first frost typically arrives Late September - Mid October. Harvest before this or frost will damage your buds. Check trichomes daily in the final 2-3 weeks.
Ready to Start Your Outdoor Grow?
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