CannaGLAP
Grow cannabis in Rockville, MD
Growing cannabis in Rockville: an early spring start, and plants that will not stop growing
Rockville hands a grower an early calendar. Seeds can go under lights by March 4, and plants can move outside on April 15, the date frost has passed in about nine springs out of ten at the Rockville station, just over a mile away.
It looks like a head start. A photoperiod plant does not flower any sooner for being planted early, though. It waits for the longer nights of late summer and simply grows until then, through June and July highs near 82°F and 87°F. With Maryland allowing two plants per residence, both kept out of public view, how big do you want each one standing by August?
Adults 21 and over: yes. Plant limit: 2 per adult; 2 per residence even with 2+ adults.
Not in public view; reasonable precautions against access by under 21s. Source: Criminal Law 5-601.2. Local rules (landlords, HOAs, city codes) can add more; this is a summary, not legal advice.
Rockville indoors, from March seedlings to a muggy September
The indoor season opens while March is still cold. Seeds started between March 4 and March 18 sprout into a month that averages about 36°F at night with about 13 freezing nights, and a basement or garage in a Montgomery County house holds that chill. Set seedlings on a heat mat, keep them off bare concrete, and let the lights run through the early morning hours.
Summer heat lingers after dark. July averages about 10 days at 90°F, and its nights only fall to about 69°F, so moving the lamp to night hours buys a few degrees rather than a fix. A tent in a condo near Rockville Town Square or an apartment off Rockville Pike does best in a room the air conditioner reaches, with the exhaust pushing warm air out of that room, not into it.
Then the air thickens toward harvest. June is the driest warm month measured, at about 62 percent humidity, which makes it a comfortable stretch for vegetative growth. By August the figure is 74 and by September 77, right as flowers fill out. Run a dehumidifier through flower, and keep a fan moving air under the canopy as well as over it.
| Month | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high °F | 42 | 45 | 54 | 66 | 74 | 82 | 87 | 85 | 78 | 66 | 56 | 46 |
| Avg low °F | 27 | 28 | 36 | 46 | 55 | 64 | 69 | 67 | 60 | 48 | 38 | 31 |
| Humidity % | 74 | 62 | 70 | 74 | 77 | 68 |
Highs and lows: NOAA 1991 to 2020 normals, Rockville 1 Ne station (1.2 miles away). Humidity: Open-Meteo historical model data, average daily humidity in 2024, for the months shown. Planning averages, not a forecast.
Rockville outdoors: a long season and a height problem
Maryland allows 2 plants per adult but no more than 2 at a residence, however many adults live there. They must stay out of public view, and you are expected to take reasonable precautions to keep anyone under 21 away from them. A plant that rises above the fence by August may no longer be out of view, so plan its height from the start.
Sow from March 4 to March 18 and plant out on April 15, once the typical last frost of April 1 is well past and nights reach a 45°F average. You then have about 192 days before an early frost on October 24; in a typical year it holds off until November 6. To keep a photoperiod plant manageable, top it early and bend its branches outward instead of letting it climb, or plant it later in spring. An autoflower started in April finishes well before September's 77 percent air arrives.
| Last spring frost | Apr 1 in a typical year, Apr 15 to be safe (later only 1 year in 10) |
|---|---|
| First fall frost | Nov 6 typical, as early as Oct 24 (1 year in 10) |
| Frost-free season | about 219 days |
| Nights stay 50°F or warmer | Apr 30 to Oct 11 |
| Start seeds or clones indoors | Mar 4 to Mar 18 |
| Move plants outdoors | Apr 15 or later |
What stays between you and your two plants
Rockville is suburban without being private: townhouse rows, condo balconies above Town Center, neighbors you pass at the Rockville Farmers Market or in the crowd at Rocktobierfest. With two plants per home, the record of how you trained each one is the whole year's lesson.
Canna GLAP encrypts those grow records on your phone before upload. Anyone who got into our servers would carry off Montgomery County grow entries with no key to open 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 Rockville ask
Why do outdoor cannabis plants get so tall in Rockville?
An April 15 planting gives a photoperiod plant months of growth before late-summer nights tell it to flower. Topping and training, a later planting or an autoflower keep it smaller and easier to keep out of public view.
When should I start cannabis seeds in Rockville?
Between March 4 and March 18, under lights indoors, for a move outside on April 15. By then frost is safely past in most years and nights average about 45°F.
How many cannabis plants can a Rockville home grow?
Two per residence, even if two or more adults live there. Keep them out of public view and take reasonable precautions so no one under 21 can get to them.
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