CannaGLAP
Grow cannabis in Broomfield, CO
Growing cannabis in Broomfield: the hottest month is also the driest one measured
Look at July in Broomfield and two numbers land on the same month. Afternoons average 91°F at the Northglenn station, 4.2 miles away, and the air averaged about 38 percent humidity, the lowest of the months measured.
A fan can handle heat. Heat in dry air is a different load: it pulls water through a plant faster than young roots can replace it. So before the next run, ask whether your tent is set up for the thermometer alone, or for both.
Adults 21 and over: yes (residents). Plant limit: 6 per resident, 3 or fewer flowering; 12 per residential property unless local law allows more.
Enclosed, locked area not openly visible; separate locked space if anyone under 21 lives there; local rules can be stricter. Source: Colorado home grow laws; 12 plant cap: HB 17-1220. Local rules (landlords, HOAs, city codes) can add more; this is a summary, not legal advice.
Building a Broomfield tent around a hot, dry July
July brings about 19 days that reach 90°F, August about 16 and June about 10. A spare-room tent near the Arista district or an upstairs bedroom off West Midway Boulevard stacks lamp heat on top of whatever the house is holding, so move the lights-on hours to the night from June through August. July nights still average about 59°F, which hands an intake fan cooler air to pull in.
Treat the dryness as its own problem. In 38 percent air, seedlings and fresh clones have the least root to keep up. Give them a humidity dome for the first week, a small tent humidifier through early veg, and a daily check of pot weight in July.
Flowering is where the same air helps. September averaged about 40 percent humidity and October about 42, so bud rot has little to work with, and a flower tent can lean on steady airflow more than on a dehumidifier.
Winter asks for heat instead. December and January lows average about 19°F, with freezing nights on about 29 of January's 31. A basement or garage tent cools hard with the lamps off, so run the light hours through the coldest part of the night and keep pots off bare concrete. January's 63 percent outdoor humidity means little once a furnace warms that air: a heated room runs dry, so keep the humidifier going.
| Month | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high °F | 48 | 50 | 58 | 64 | 72 | 85 | 91 | 89 | 82 | 67 | 56 | 48 |
| Avg low °F | 19 | 20 | 28 | 35 | 44 | 53 | 59 | 57 | 49 | 37 | 27 | 19 |
| Humidity % | 63 | 42 | 38 | 46 | 40 | 42 |
Highs and lows: NOAA 1991 to 2020 normals, Northglenn station (4.2 miles away). Humidity: Open-Meteo historical model data, average daily humidity in 2024, for the months shown. Planning averages, not a forecast.
Outdoors in Broomfield County
Colorado lets residents grow at home only in an enclosed, locked space that is not openly visible, and if anyone under 21 lives in the home, the grow needs a second locked space of its own. Local rules can be stricter, so read Broomfield's own code before you build. The limit is 6 plants per resident, no more than 3 flowering, and 12 per residential property unless local law allows more.
If your space qualifies, start seeds April 6 to 20 and move plants out May 18 or later. Frost usually ends around May 2 and May 14 is the safe date, but the average night does not warm to 45°F until May 18. An early fall frost can come by September 26, about 131 days later. Autoflowers fit that window; a photoperiod plant needs to be bred to finish by late September.
| Last spring frost | May 2 in a typical year, May 14 to be safe (later only 1 year in 10) |
|---|---|
| First fall frost | Oct 11 typical, as early as Sep 26 (1 year in 10) |
| Frost-free season | about 160 days |
| Nights stay 50°F or warmer | Jun 4 to Sep 11 |
| Start seeds or clones indoors | Apr 6 to Apr 20 |
| Move plants outdoors | May 18 or later |
| Season note | Frost can arrive before mid October here: long flowering plants may not finish outdoors |
Your Broomfield grow, kept to yourself
Growers talk. At the BrewHaHa Craft Beer Festival or Broomfield Days, a good harvest story is easy to tell. The notes behind that story took seasons to earn, and they are worth more kept quiet.
Canna GLAP encrypts each grow entry on your phone before anything is uploaded. Anyone who cracked our servers would leave with grow records in scrambled form, and we hold no usable key to open them. The numbers behind the story stay with the grower who earned them.
What is encrypted: your plants, notes, photos, feed logs and harvests. What is not: account details (such as your email, name and plan), a grow name or town if you type one, your team, and your sensors' names. The full list: what a hacker would get.
Questions growers in Broomfield ask
When should I plant cannabis outside in Broomfield?
May 18 or later. Frost usually ends around May 2 and May 14 is the safe date, but nights stay cooler than 45°F on average until May 18. Start seeds indoors April 6 to 20.
Does Broomfield's summer heat hurt an indoor grow?
It can. The Northglenn station averages about 19 days of 90-degree heat in July and 16 in August. Run the lights at night and pull in the cooler night air, which averages about 59°F in July.
Do I need a dehumidifier to flower in Broomfield?
Not for the outside air. September and October averaged about 41 percent humidity, so airflow does most of the work; a humidifier for seedlings and clones is the more useful buy.
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