Ask Erik - Proper size for grow room

Thanks for your question, Sam. This is definitely on the tighter side as far as vertical space allowances go, but with the right plant variety and methods you should be able to pull off a moderate harvest. Although the lamps may be able to touch the plants, if they are kept too close to the canopy, you will have poor light distribution, reducing the effective coverage of each of the lamps. A 90–125-W high-output compact fluorescent should cover about 2 x 2 ft. Don’t expect the yield to be as substantial as with HID lighting on a per square foot basis.

Although the lamps run relatively cool compared to HID lamps, there is still a significant amount of heat generated, which will need to be dissipated away from the growing area. An exhaust fan will likely be required. It may also be possible to air-condition the area or draw in cool air from an adjoining air-conditioned room. The cooling system should be wired to a cooling thermostat. High humidity or temperatures will increase stretching in the plants, something you don’t have the height for.

To conserve height you may consider just hanging the CF lamps vertically, without shades. If you cover all of the surfaces with a reflective material, the plants will receive a lot of reflected light. You may also consider adding side lighting by way of T-5–type high-output fluorescents. Water-cooled or air-cooled reflectors may allow you to use HID lighting in the space.

You will need to start the garden with very healthy cuttings. You will not have an inch to spare, so no time and height can be wasted in getting the plants into a vigorous vegetative phase. You should initiate flowering immediately after transplanting 6-in. rooted cuttings into your flowering room. Make sure you have a variety that is known to stay compact, even under a range of growing conditions. High planting densities will be required — about one rooted cutting per 6-in. square under the 2 x 2-ft. light footprint. You may also train fewer plants per square foot to grow along a screen or mesh, bending and pruning to keep a low growing profile.

Maintain slightly lower nutrient levels during the first half of flowering to help keep the plants from stretching. Four- or 6-in. rockwool cubes or coco blocks should provide sufficient root space for compact plants and are very short in height relative to containers. You could just place trays filled with cubes underneath the lights and hand water as necessary. If this is an upstairs space, you could plumb a flood and drain setup with the reservoir and pump in the room below. If you choose to hand-water, you might also consider just filling the trays with a high-quality soilless mix. You will have to water less frequently, but lose some of the flexibility in being able to move the plants around — an important consideration with your height restrictions to maximize light use efficiency. Deep-water culture (DWC) might also be an option. Whatever method you choose, limit the height of the growing vessel to between 4 and 6 in.

There are nutrient supplements available at hydroponics shops that will help control vertical growth after flowering is initiated. Personally, I prefer to stay away from these, but they might become necessary for your growing situation.

A creeper (auto mechanic supply) might help you get around in your low growing garden. I trust you are not the claustrophobic sort. Good luck and good growing to you.

Cheers,
Erik Biksa