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running one plant in a 2x2, here's what changed
dropped from two plants to one last run and honestly the difference in smell management was noticeable from day one. less canopy surface area, less transpiration, less off-gassing from the soil. my 4 inch carbon filter was struggling before. same filter, one plant, zero issues through late flower.
vertical space matters more than floor space in a small closet. i run a single fabric pot center-stage and train the plant to fill the footprint wide, not tall. keeps the canopy close to the light and away from the filter intake so air actually moves through the room before it gets scrubbed.
if smell is your main concern and you're in a tight spot, fewer plants is the move. one well-fed, well-trained plant can fill a 2x2 and still pull solid weight. you don't need to pack the space to use the space.
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The smell point is real, but I'd push back slightly on framing it as a plant count issue. Transpiration rate scales with canopy size and VPD, not headcount directly. One plant trained wide to fill a 2x2 can move just as much moisture as two smaller untrained plants. If your filter was struggling before and isn't now, it's worth asking whether the first run also had higher humidity or a wider VPD swing that was driving more transpiration. The variable might not be what you think.
That said, the training argument is solid and underrated. One plant center-stage with proper LST or a manifold will almost always outperform two plants crammed in and competing for light penetration. I run a 4x4 but I've done single-plant runs for testing purposes and the canopy control is genuinely easier. You can dial in the shape precisely instead of managing two separate root zones and growth rates.
The filter airflow point is the part I'd actually emphasize over everything else. A lot of people size their fan and filter for the room volume and forget that canopy obstruction and poor circulation kill efficiency before the filter even does its job. Positioning matters as much as CFM rating.
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