CannaGLAP
Grow cannabis in Los Altos, CA
Growing cannabis in Los Altos: September's warm afternoons arrive in damp air
In Los Altos, the year's warmest afternoons come in September. The Moffett Federal Airfield station, 3.9 miles away, puts that month's average high near 78°F, and about 3 of its roughly 9 yearly 90°F days fall then.
The same month carried the dampest air of June through October in 2024: 70 percent, up from 58 in June. Heat and moisture call for different tools, and a September flower room needs both. Which one is your setup missing?
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.
A Los Altos flower room in September
Treat September as two problems that share a week. On a hot afternoon, an air conditioner cools the tent and pulls water from the air while it runs. Then nights fall to about 57°F, the unit sits idle, and the damp creeps back. The dehumidifier works those hours, so it carries the humidity plan; the air conditioner only helps.
Put the dehumidifier on a humidistat (a switch that turns it on above a humidity you choose), keep a fan moving air under the canopy, and leave space between colas, the dense top buds, since a crowded canopy traps moisture where buds are thickest.
The light schedule has room to bend. With so few hot afternoons, the lamp can run by day through most of the summer. In September, shift it to the night when a hot spell is forecast, so the dark period covers the heat.
Winter is gentle but not frost-proof. Lows average about 42°F at midwinter, and the station counts about 2 freezing nights a year, so a garage tent wants its lamp on through the coldest hours and a seedling mat under young plants. January air read 83 percent outdoors in 2024, but a heated room dries that out; only an unheated garage needs a dehumidifier in winter.
| Month | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high °F | 59 | 62 | 65 | 68 | 72 | 76 | 77 | 77 | 78 | 74 | 66 | 59 |
| Avg low °F | 42 | 45 | 47 | 49 | 53 | 56 | 59 | 59 | 57 | 53 | 46 | 42 |
| Humidity % | 83 | 58 | 62 | 66 | 70 | 57 |
Highs and lows: NOAA 1991 to 2020 normals, Moffett Federal Airfield station (3.9 miles away). Humidity: Open-Meteo historical model data, average daily humidity in 2024, for the months shown. Planning averages, not a forecast.
Los Altos outdoors: flowering through September
California permits 6 living plants per private residence, the same cap however many adults share it, in a locked space no passerby in a public place could spot. Cities and counties can make reasonable rules for indoor grows, short of a ban, and can ban outdoor grows, so check the local rules that cover your address first.
If outdoor plants are allowed at your address, sow indoors from March 4 to 18 and plant out from April 15, though nights average below 50°F until April 25. An outdoor photoperiod plant flowers through September whatever you choose, so the variety sets the finish. One that ripens in October meets drier air, 57 percent in 2024, at the cost of nights near 53°F. One that ripens in September escapes the chill but finishes in that month's damp. Either way, prune the inside of the plant so air moves through it.
| Frost | Rare: about 2.4 freezing nights a year |
|---|---|
| Nights stay 50°F or warmer | Apr 25 to Oct 30 |
| Start seeds or clones indoors | Mar 4 to Mar 18 |
| Move plants outdoors | Apr 15 or later |
A quiet grow in a quiet town
Los Altos is quiet and residential, with a walkable village downtown along Main Street and State Street and a weekly farmers market there. If you trade tips with another grower at the market, what you hand over should be your choice, not whatever your notes app gives up.
With Canna GLAP, the grow journal is encrypted on your phone and uploaded only in that form. A thief who got into our servers would leave with grow records turned unreadable and no key to undo it. That covers the journal; it cannot mute a fan or hide the smell of a flowering plant on a warm September evening.
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 Los Altos ask
What is the hardest month for a Los Altos grow?
September. It has the warmest afternoons, and in 2024 it had the dampest air of June through October, so a flower room needs cooling on hot days and dehumidifying on cool nights.
Does it freeze in Los Altos?
Rarely. The Moffett Federal Airfield station averages about 2 freezing nights a year, mostly in December and January, and average nights stay at 45°F or warmer from February 22 to November 25.
Do I need air conditioning for a Los Altos grow tent?
For most of the year, no: the station averages about 9 afternoons a year at 90°F. It helps on September's hot days, but it dries only while it runs, so pair it with a dehumidifier.
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