CannaGLAP
Grow cannabis in Northglenn, CO
Growing cannabis in Northglenn: June arrives 13 degrees hotter than May
In Northglenn, spring does not ease into summer. It jumps. May afternoons average 72°F at the Northglenn station, 1.7 miles away and 5,407 feet up, and June afternoons average 85, with about 10 days at 90 or hotter where May had about 2.
A plant set outside on May 18 gets a few weeks to adjust before that heat lands. A clone moved from a cool May tent into a June one gets less. Is your setup ready for the switch before the calendar forces it?
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.
Indoors in Adams County: two setups, a few weeks apart
May is still a heating month inside a garage or basement tent. Nights average about 44°F, and a tent that slips into the 50s with the lights off slows young roots. A small heater on a thermostat and a seedling mat cover it.
By mid June the same tent needs the opposite. July averages 91°F, with about 19 days at 90 or hotter, and August about 16. Switch the lights to the overnight hours as June starts and add an exhaust fan sized for the space, so the dark period falls across the hottest afternoons. Nights cool to about 59°F in July, which keeps the lamps manageable.
The air dries out as the heat builds. July averages 38 percent humidity, the driest of the months measured, and June 41. Clones and fresh transplants lose water fastest just as the heat arrives, so a humidifier in the tent through the first weeks of veg does more in June than any change to the feed.
Winter is long and cold: about 149 nights a year reach freezing, with December and January lows near 19°F. Lights through the coldest hours and pots raised off the slab keep a winter run on schedule.
Heater safety: use one with tip-over and overheat shutoff, plug it straight into a wall outlet (not an extension cord or power strip), and keep it a few feet from tent fabric and plants.
| 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 % | 64 | 41 | 38 | 46 | 39 | 42 |
Highs and lows: NOAA 1991 to 2020 normals, Northglenn station (1.7 miles away). Humidity: Open-Meteo historical model data, average daily humidity in 2024, for the months shown. Planning averages, not a forecast.
Your Northglenn outdoor window
Colorado lets residents grow up to 6 plants each, with 3 or fewer flowering at once, and 12 per residential property unless local law allows more. Every plant has to be in an enclosed, locked area that is not openly visible, and anyone under 21 in the home means a separate locked space for the plants. Local rules can be stricter, so check Northglenn's before you build.
If your space qualifies, start seeds April 6 to 20 and set plants out May 18, when nights first average 45°F, four days after the May 14 safe frost date. Shade them through their first run of June heat. An early frost can arrive by September 26, about 131 days later, and nights fall back below a 45°F average from September 25, so autoflowers and fast photoperiods that finish in September are the plants to choose.
| 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 |
Summer crowds, a quiet grow
Northglenn's summer runs through E. B. Rains Jr. Memorial Park, from the Summer Concert Series to the Food Truck Carnival, much of it on the Festival Lawn by Webster Lake. In a suburb of about 38,000 where neighbors meet that often, someone may notice a tent fan humming in your garage.
Your records do not have to be as easy to spot. Canna GLAP encrypts your grow log on your phone before upload. If someone got into our servers, they would get unreadable grow data and no key to open it. The June heat plan that kept your clones alive is yours to pass along or keep.
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 Northglenn ask
When should I switch my tent lights to nighttime in Northglenn?
As June begins. June brings about 10 days at 90°F and July about 19, while May has about 2, so the change pays off within weeks.
When can I plant cannabis outside in Northglenn?
Move plants out May 18, after the May 14 safe frost date and once nights average 45°F. Seeds go in April 6 to 20.
How long is the outdoor season in Northglenn?
About 131 days, from May 18 to an early frost by September 26. A typical first frost holds off until about October 11, but plan to harvest by late September.
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