grow roomGet the specific guidelines on how to maximize your marijuana grow room environment and materials. © Copyright, Steve Davis, 2016

Marijuana Grow Room Guide for Maximum Bud Size & Potency

What you do or don’t do to manage your hydroponics marijuana grow room has a huge impact on your harvest weight and bud potency.

That’s why we’re giving you this exclusive description of the specific ideal conditions for growing marijuana indoors.

The closer you get to making your marijuana grow room have these conditions, the closer you get to marijuana maximum yield!

GROW ROOM TEMPERATURE: During lights-on cycle without added C02, 73-77°F.

Ideal day cycle temperature with maximum C02 augmentation at 1100 ppm C02: 84F.

During lights-off cycle, between 66-70F.

Notes: Watch your cannabis strains to see if temperature stress is affecting them.

Some varieties of marijuana need slight adjustments to day and night temperatures.

ROOT ZONE TEMPERATURE: 67-68F. If you’re growing in basements and/or on cement slabs, don’t put pots directly on the floor, as this can cool the root zone too much, especially in colder months.

WATER/NUTRIENT SOLUTION TEMPERATURE: 66-68F. Warmer temperatures in nutrients solutions contributes to growth of harmful organisms in hydroponics reservoirs.

Warmer temperatures can slow root function and deter root growth.

You may have to add a hydroponics chiller to cool nutrients water if your grow room is too hot.

If your water is too cold, you may have to add an aquarium heater to your reservoir.

GROW ROOM RELATIVE HUMIDITY: Grow room humidity is more complicated than most growers realize.

The relationship between relative humidity and temperature is part of calculating the correct “vapor pressure deficit” (VPD) your plants need.

VPD is extremely complicated and will be dealt with in its own article.

The simplest way of understanding how it impacts your grow room is that the higher the temperature, the higher relative humidity your grow room needs.

And the reverse is also true.

In general, the following guidelines are useful.

Your grow room relatively humidity should be 58-75% during vegetative phase and between 52-65% during bloom phase.

Excess humidity creates conditions that allow mold, powdery mildew, and other harmful organisms to flourish, which can destroy your buds.

It can drown your leaves in air-borne moisture, which interferes with leaf “breathing.”

Insufficient humidity means your marijuana leaves evaporate too much water.

This strains your marijuana roots (because they have to intake more water) and creates other problems such as fertilizer burn.

Read here for more information about the all-important vapor pressure deficit.

LIGHT CYCLES: Vegetative Growth: 17-18 hours on, 6-7 hours off every 24 hours.

Floral triggering and bloom phase: 12 hours on, 12 hours off.

Note that for auto-flowering marijuana you run 18-24 hours of light from start to finish.


For clones and seedlings: T-5 high-output fluorescent lighting or LED grow lights.

For veg phase growth with plants more than two weeks old, depending on the size of your grow room and whether you’re using photoperiod marijuana or autoflowering, you can run LEDs, plasma, T5s or metal halide (MH).

Lighting for Marijuana Bloom Phase:

High Pressure Sodium/Metal Halide in combination, with more HPS than MH.

High quality LED lights such as Lush Lighting LED grow lights.

If you have a very small grow space using SCROG, Sea of Green, grow chambers, grow tents, or autoflowering marijuana, you could use a T-5 high output fluorescent.

LIGHT COVERAGE: For stationary lights, one 400 watt HID bulb provides adequate light for 8-9 square feet of space.

A 1000-watt light provides adequate light for 16-22 square feet of space in a hydroponics marijuana grow room.

The use of light movers extends these coverage areas.

For a 600-watt Lush Lighting LED grow light, you have 12-16 square feet of coverage.

LIGHT REFLECTION: Reflective materials such as Mylar, white glossy poly plastic or similar materials on all marijuana grow room walls.

Aluminum foil, mirrors, and white paint do not have adequate degrees of reflectivity.


All guidelines are approximate.

Hold your hand under the light where your leaves are.

If your hand feels like it’s too hot, your leaves are too hot, so move the light higher.

STERILE ROOT ZONE: Grodan Rockwool, coco coir, lava rocks, vermiculite, perlite, clay pellets, deep water culture.

GROW ROOM ATMOSPHERIC REQUIREMENTS: Marijuana plants need oxygen, including in the root zone.

They also sufficient amounts of carbon dioxide (C02), especially at underside of leaves.

Ideal total ambient C02 in your marijuana grow op should be between 900-1600 parts per million during lights-on cycle.

Natural C02 levels are approximately 395 ppm.

Your C02 emitter should be timed in relation to exhaust fan so that C02 is not sucked out of room.

Don’t add C02 during lights-off cycle.

AIR CIRCULATION (INTERNAL): Circulation by at least one medium size oscillating fan for any size grow space, no matter how small.

For larger hydroponics marijuana grow spaces, at least one medium or large-size oscillating fan for every 1000-watt light.

You should be able to feel and “see” air movement in your grow space at plant level so that all plants’ leaves are in a gently moving ocean of fan-driven air.

AIR EXCHANGE: Install exhaust fans sufficient to totally exchange all air in grow space every three minutes.

Exhaust fans must be timed relevant to C02 augmentation to avoid removing augmented C02 from your hydroponics marijuana grow room.

Read this important article on grow room exhaust fans.

IDEAL pH OF GROW MEDIA AND NUTRIENT SOLUTION/WATER: Between 5.7 and 6.1. Use pH Perfect base hydroponics nutrients to eliminate worries about pH.

IDEAL SOIL pH: 6.4. Use pH Perfect base nutrients to eliminate worries about pH.


Nutrients intensity varies widely.

You have to watch your plants closely because nutrient burn is an epidemic in our marijuana growing community, especially during bloom phase.

In general with established marijuana plants, start by running half the manufacturer’s recommended nutrients dose and go up (or down) from there.

If you’re running more than 1300 ppm, and especially if you don’t flush periodically, you may toxify your root zone and marijuana plants with excess nutrients salts.

A sure sign of nutrients burn is leaf tips that are browning.

IDEAL WATER: Rainwater, or reverse osmosis water.

Tap water and well water are almost always polluted in ways that harm your root zone and marijuana plants.

GROW ROOM SECURITY: Filtered air intake and outflow, scrubbed in both directions to remove contaminants and odor.

No pets, debris or other polluters in the grow room.

Install video monitoring, motion sensors.

Don’t tell anybody you grow marijuana.

The specifics we gave you in this article may have to be slightly adjusted to accommodate your marijuana grow room.

Establish the best conditions in your grow room, and get more weight and THC from your marijuana plants!

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