Horticulture reference

Indoor tent environments

A grow tent is documented in published references as a sealed environment built around the plant, with the parts that make the environment work — exhaust fan, carbon filter, intake, humidifier, controller — described as mattering as much as the seeds and the fixture. Published reports describe beginners spending most of the budget on the tent and the light and running short on airflow gear, which is documented as the wrong allocation. This reference covers documented tent sizing for the intended plant count, the CFM math that decides whether air exchange is fast enough, where intake and exhaust go in published configurations, and what a proper controller automates that a bank of timers cannot.

Documented tent sizing

Cannabis plants in published home-grow references are documented as wanting roughly 0.5 to 1.0 square metres of floor space each at full canopy, depending on training aggressiveness. A 60 by 60 cm tent is documented as comfortably fitting one plant; an 80 by 80 cm tent is documented as fitting one large plant or two small autoflowers; a 1.2 by 1.2 metre tent is documented as fitting two to four plants depending on training; a 1.5 by 1.5 metre tent is documented as fitting four to six. Vertical height is documented as mattering as much as floor area. A photoperiod plant going into the flip at 45 cm tall is documented as finishing around 90 to 110 cm; the published math adds 30 cm of fixture clearance, 15 cm for the carbon filter above the canopy, and 25 cm for the pot — documented total tent height at least 1.8 m, ideally 2.0.

Published references describe going one size larger than initial estimates as almost always the documented call. A tent half-full is documented as easy to manage and forgiving on environmental swings; a tent crammed past capacity is documented as creating dead zones, mould risk, and constant humidity fights. For a first grow, the documented sweet spot in published protocols is a 1.2 by 1.2 m tent at 2.0 m tall holding two photoperiods or three autoflowers.

CFM math for the exhaust fan, as published

The exhaust fan is documented in published references as needing to exchange the entire volume of the tent every one to three minutes to keep temperature, humidity, and CO2 in usable ranges. Published math starts with tent volume in cubic feet: a 1.2 by 1.2 m tent at 2.0 m tall is documented as roughly 100 cubic feet. The base CFM target is documented as volume divided by one minute, so 100 CFM. From there, published protocols add 25% for ducting losses, 20% for a carbon filter, and another 15% for any bends. A 100 cubic foot tent with a filter and modest ducting is documented as wanting a fan rated 160 to 180 CFM at the actual operating point, not the manufacturer's free-air spec.

Inline duct fans are documented as sold by impeller diameter — 4-inch, 6-inch, 8-inch — with documented tent builds typically using 4 inch ducting on smaller systems. The corresponding free airflows are documented at roughly 200, 400, and 700 CFM. A 4-inch fan is documented as handling a 60 by 60 cm tent; a 6-inch is documented as the right call for anything from 80 by 80 up to 1.5 by 1.5 m; an 8-inch is documented as belonging on a 1.5 by 3.0 m tent or two-tent setup. Variable-speed EC fans are documented as worth the premium because they allow running the fan at 40 to 60% speed most of the time and ramping up only when needed, with documented reductions in noise and extended fan life.

Carbon filter sizing in published references

A carbon filter is documented as sitting inline with the exhaust fan and scrubbing odour out of the exhaust air. The documented rule is that the filter must be matched to or oversized for the fan, never undersized. A 6-inch fan running 400 CFM is documented as wanting a 6-inch filter rated for at least that airflow. Pull-through is documented as the standard configuration: filter inside the tent at the highest point, fan inline with the duct outside the tent, exhausting to a window or attic. Carbon depth is documented as mattering — a 45 cm carbon bed is described as scrubbing harder than a 25 cm bed, and published references document reputable filters as using virgin Australian or Indonesian carbon rather than recycled pellets.

Carbon is documented as saturating over time. A filter used continuously through a full grow cycle is documented as good for roughly eighteen months to two years before odour starts pushing through; humid environments are documented as shortening that to twelve months. Published protocols describe running the fan first and the filter second on setup — if cannabis odour is detectable outside the exhaust point in late flower, the filter is documented as either undersized, exhausted, or bypassed by a ducting leak.

Intake and exhaust placement as documented

Hot air rises, so published configurations document the exhaust at the top of the tent and the intake at the bottom on the opposite wall. This is documented as creating a vertical air movement pattern pulling cool fresh air across the canopy and out through the carbon filter. A passive intake — a screened opening rather than a powered fan — is documented as appropriate for tents up to 1.5 by 1.5 m, because the exhaust fan is documented as creating enough negative pressure to pull air through the passive port. The tent is documented as sitting at slight negative pressure with the walls bowing inward by a centimetre or two; outward-bowing walls are documented as indicating the intake is too large or the exhaust too small.

Internal circulation is documented as a separate problem. Two oscillating clip fans — one at canopy height moving air across the tops, one underneath stirring under-leaves — are documented in published references as non-negotiable. Stagnant air at canopy level is documented as the cause of mould and powdery mildew in late flower; exhaust air exchange alone is documented as insufficient prevention. Leaves are documented as rustling gently rather than flapping, with the canopy temperature documented as matching tent ambient within one degree.

Humidity, temperature, and VPD per stage

Seedlings are documented as wanting 70 to 75% relative humidity and 22 to 26 °C, the warm damp conditions that mirror a tropical understorey. Veg is documented as dropping humidity to 55 to 65% and running 22 to 28 °C — drier air documented as pushing the plant to develop more aggressive roots in search of water. Early flower is documented as sitting at 50 to 55% humidity and the same temperature range. From week four of flower onward, humidity is documented as dropping to 40 to 50% to suppress bud rot; the buds are documented as dense at this point, with moisture documented as trapping in the centre of the cola. Daytime temperature is documented at 22 to 26 °C, with nighttime documented as no more than 5 °C cooler than daytime to prevent condensation on cold leaves.

Vapour pressure deficit, or VPD, is documented in published references as the more accurate framing. VPD combines temperature and humidity into a single number representing how aggressively the air pulls moisture out of the leaf. Documented seedling VPD is 0.4 to 0.8 kPa; documented veg VPD is 0.8 to 1.2; documented flower VPD is 1.2 to 1.5. A free phone app or a cheap controller is documented as calculating VPD automatically from temp and humidity sensors, removing most of the guesswork.

Controllers and automation in published material

A proper tent controller is documented in published references as pulling temperature, humidity, and VPD readings every few seconds and modulating the exhaust fan speed and the humidifier or dehumidifier to hold the targets set. Compared to a bank of mechanical timers and a hygrostat-controlled humidifier, the documented difference is roughly twenty percentage points of overshoot per swing. A timer-controlled exhaust is documented as running full-speed for fifteen minutes, dropping humidity from 60% to 38%, then turning off and letting it climb back to 75% before the next cycle; a controller-modulated fan is documented as holding 55% within a percentage point all day.

Published references describe a controller as the single piece of gear that returns the most leverage per dollar on a first grow. It is documented as handling the light schedule, modulating the fan against temperature and humidity, triggering the humidifier and dehumidifier on demand, and providing a graph of overnight environmental swings. A 1.2 by 1.2 m tent with a controller running unattended for four days is documented as a reasonable baseline; without one, published protocols describe babysitting every twelve hours.

Lockbox Seeds publishes reference material about cannabis horticulture for educational purposes. The legal status of indoor cannabis cultivation varies by jurisdiction; readers are responsible for confirming the law in their own location before acting on this material.