CannaGLAP
Grow cannabis in Pasadena, CA
Growing cannabis in Pasadena: the heat season starts early and ends in your harvest
Pasadena's weather station sits in the city itself, at 864 feet, and its averages show 90°F afternoons in every month from February through November: about 74 a year in all. August averages a 91°F high. October, when plants flowering on the natural season are ripening, still averages about 8 days of 90°F or more.
The air dries out as the heat lingers. Humidity averaged 68 percent in June, then fell to 50 in October, the lowest of the months measured. So the question in Pasadena is not mold at harvest. It is whether your buds finish in a heat wave.
Adults 21 and over: yes. Plant limit: 6 living plants per private residence, however many adults live there.
Locked space, not visible from a public place; cities and counties can set reasonable rules for indoor grows (but cannot ban them) and may ban outdoor grows; a landlord may prohibit growing on a rental. Source: Department of Cannabis Control; conditions: Prop 64 text as passed in 2016 (H&S Code 11362.2 and 11362.45). Local rules (landlords, HOAs, city codes) can add more; this is a summary, not legal advice.
Cooling a Pasadena flower room through fall
Plan the cooling around August, September and October. Those months average about 19, 16 and 8 days that reach 90°F, with highs of about 91, 90 and 83°F. A tent in a Playhouse District apartment or a garage a few blocks off Colorado Boulevard can run well above the room on those afternoons. Move the lamps to the night hours from July through October, when August lows near 63°F give the exhaust cooler air to pull in.
Heat in late flower shows up in the jar. A canopy that runs hot in its final weeks tends to lose aroma and can push loose new growth out of finished buds. Hold the canopy under about 80°F with the lights on in those weeks, even if that means running an air conditioner on the hottest days.
June runs the other way. At 68 percent humidity, the dampest of the months measured, and with highs near 84°F, it is a comfortable month for clones and young plants, and a dome can come off sooner than it would in October air. Flowering plants in June need a fan under the canopy and little more.
The dry fall air returns after harvest. At 50 percent, October can dry hanging branches in a few days, which leaves a harsh smoke. Dry in a closed space with fewer fans, or a small humidifier, so the process takes a week or more. Winter stays gentle, with lows near 45°F in December and 46 in January, so a heat mat for seedlings covers the cold side.
| Month | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high °F | 68 | 69 | 73 | 76 | 78 | 84 | 89 | 91 | 90 | 83 | 75 | 67 |
| Avg low °F | 46 | 46 | 48 | 51 | 54 | 58 | 62 | 63 | 62 | 56 | 50 | 45 |
| Humidity % | 64 | 68 | 61 | 57 | 60 | 50 |
Highs and lows: NOAA 1991 to 2020 normals, Pasadena station (0 miles away). Humidity: Open-Meteo historical model data, average daily humidity in 2024, for the months shown. Planning averages, not a forecast.
Planting outside in Pasadena
Pasadena homes fall under California's limit of 6 living plants per private residence, however many adults live there, and the plants must be grown in a locked space that no one can see from a public place. Cities and counties can regulate home grows and may ban them outdoors, so look up Pasadena's code before planning a yard grow.
Where it is allowed, sow seeds between March 4 and March 18 and set plants out from April 15. Frost will not end the season; heat shapes it. Average lows hold at 50°F or above from April 7 to November 14, and plants flowering into October meet about 8 days at 90°F that month. Give them afternoon shade, mulch and deep watering, or choose a variety that finishes in late September, ahead of the October spells.
| Frost | Rare: less than 1 freezing night a year on average |
|---|---|
| Nights stay 50°F or warmer | Apr 7 to Nov 14 |
| Start seeds or clones indoors | Mar 4 to Mar 18 |
| Move plants outdoors | Apr 15 or later |
A Pasadena grow, kept to yourself
Pasadena does crowds well: the Rose Parade, the Rose Bowl Flea Market, the Pasadena Certified Farmers Market, an evening in Old Pasadena. Somewhere in those crowds is a grower who would like to know how you kept a canopy cool through an October heat spell. You get to decide what to tell them.
Canna GLAP encrypts the grow journal on your phone before it is uploaded, so a thief who got into our servers would leave with scrambled grow records and no key. The settings that carried your plants through August are yours to 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 Pasadena ask
How many 90 degree days does Pasadena get?
About 74 a year at the Pasadena station, with about 19 in August, 16 in September and 15 in July. October still averages about 8.
Does Pasadena get frost?
Almost never: the station averages about 0.1 freezing nights a year. Nights do average below 45°F for a short stretch in mid to late December.
Is mold a problem for Pasadena growers?
Less than heat is. Humidity fell to 50 percent in October, the lowest of the months measured, and September averaged 60. Keep air moving under the canopy, but put most of your effort into cooling.
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