A well designed garden maximizes yield, saves time, and is more safe than a poorly planned garden. This article discusses different aspects of indoor garden design.
How many and how much light you’ll need depends on the total area of plants you want to illuminate.
When planning your garden it is helpful to think ahead to what type of plant you will be growing. Sativa plants require approximately 66 watts per square foot of space. Indicas require 40-45 watts per square feet (although they would do better with more light).
The table below can give you an estimate of how much HPS light you need to cover a square growing area.
|Floor space||HPS light||Watts per square foot|
|2′ x 2′ (60x60cm)||250 watt||62.5|
|2.5′ x 2.5′ (76x76cm)||400 watt||64|
|3.25′ x 3.25′ (100x100cm)||600 watt||56.8|
|4′ x 4′ (120x120cm)||1000 watt||62.5|
How to calculate light requirements
For example, if you have an 8′ x 4′ (240x240cm) grow area (32 square feet) that you want to illuminate with 60 watts per foot, multiply 60 watts by your total square footage of 32. The answer of 1920 is the total amount of watts needed. 2, 1000 watt lights is one solution. 3, 600 watt lights would also work.
600 watt lights are the most efficient type of HPS light, and can help spread light more evenly compared to using 1000 watt lights.
Having the right amount of lights is just part of the battle. You also need to make sure you are using the light efficiently so that waste is minimized. Good grow room design uses light positioning, reflection, and trellising techniques to ensure that the lights can do their job.
HPS and metal halide bulbs emit most of their light from the sides. So in most cases (with the exceptions of vertically designed growrooms – described below) the bulb should be mounted vertically inside a reflector.
They should also be adjustable with chains or ropes to keep them at a good distance from the canopy. Check the chart below for suggested distances.
|Distance from canopy||HPS light|
|6″-8″ (15x20cm)||250 watt|
|9″-12″ (23x31cm)||400 watt|
|12″-18″ (31x46cm)||600 watt|
|18″-26″ (46x67cm)||1000 watt|
Depending on the size and shape of your space it could be more advantageous to use more lights with less power than fewer lights with more power in order to achieve a more even spread. Aim for a consistent spread of light over your grow area. 600 watt lights are often better than 1000 watt lights for providing even coverage, and also have the benefit of being the most efficient type of HPS light.
A lot of light scatters and is wasted if it is not directed at the plants using reflection. A reflector for the bulb reflects light down towards the canopy. Choose a shape of reflector that works best with the footprint of your space, providing even coverage.
Covering the walls with mylar or white plastic sheeting improves efficiency of the lights by bouncing rays back onto the plants’ sides.
Trellising in your indoor garden positions the plants branches so the bud sites are not blocked and receive the maximum amount of light. There are a variety of ways to do this. Bamboo stakes are a popular choice. You tie branches to the stakes so that bud sites are in the best positions. A net strung across the canopy that you tie the branches to is another technique for securing the bud sites into optimal positions.
Water and lighting equipment do not mix. Bulbs can easily shatter if they come into contact with water so they should be covered by hoods with glass fronts. Wires should be safely secured so they will not get wet. Ballasts should also be mounted or secured and kept away from water – preferably out of the grow room altogether.
Preventing mold and water damage
If you are growing indoors in a house mold and fungus should be top concerns. Protect your house and your plants from any damage that could be caused by humidity. Create an enclosed space and add plenty of air circulation.
Encapsulate your grow area using a commercial grow box, or by building a frame out of wood with plastic sheeting stapled to all sides – including the floor. This will help prevent water spills from staining your floor and will keep moisture contained so it doesn’t get into the walls and ceiling of your house where it can cause mold.
Build an air ventilation system with a fresh air intake into the grow room and a fan that sucks air out. Also, set up a separate fan(s) that create air currents inside the grow area. Ventilation helps prevent humidity build up that leads to mold and fungus.
Plants require CO2 for photosynthesis. Fans not only prevent mold and fungus, they help maximize growth and yield by delivering CO2 to your plants.
Air currents gently bend plants stems, making them stronger, leading to healthier plants.
How to calculate your air circulation requirements
To supply adequate CO2 your ventilation fan should me able to replace the air in your grow room every 5 minutes. This is the absolute minimum. If you are also reducing heat from the lamps by running hoses through the light hood, and/or reducing smell by drawing the air through a carbon filter, you will need to increase fan strength to replace the air every 3 minutes or less.
To calculate the strength of fan you need first figure out the room volume. Fans are rated by CFM. This stands for cubic feet per minute and it tells you how much cubic feet of air the fan moves per minute.
For example, a room that is 10x10x10 (1000 cubic feet) needs a fan that is rated 1000 cubic feet per minute (1000 CFM) to replace the air every 1 minute.
To replace every 5 minutes, divide by 5. A fan to replace the air of a 1000 cubic feet grow room every 5 minutes needs to be 200 CFM.
To replace every 3 minutes, divide by 3. A fan to replace the air of a 1000 cubic feet grow room ever 3 minutes needs to be 333 CFM.
The ideal temperature range for growing marijuana is 68º-85º F (20º-29ºC). Temperatures above 90ºF (32ºC) cause growth to slow, so its important to prevent heat from building up inside your grow room.
An air cooled light hood is an excellent way to control heat. It has a glass bottom and ports at either side. You attach flexible tubing to your fan and blow the air out of your grow room through tubes that are attached inline with your light hoods. This technique can reduce heat by 60-80% which is usually enough to manage temperature.
Install an air conditioner and thermostat if venting the heat from the lamps is not enough to keep your grow room within 68º-85º F (20º-29ºC).
The best way to control smell is with a carbon filter. Air that is expelled out of the grow room is first pulled through a carbon filter – usually inline with your air ventilation system – which removes smell.
Dust can settle on leaves and block light and air, inhibiting growth. A hepa filter standalone unit or inline with your ventilation system helps prevent dust. An ionizer is also an effective remedy, but can’t be used in the last 2 weeks of flowering because it has a side effect of removing desirable smells from your buds.
Horizontal gardens are the most common orientation and the easiest to set up with a wide range of hydroponic systems.
Plants are on an even horizontal plane, either on tables or the floor, with the lights directly overhead. The bulbs of the lights are usually mounted vertically in a reflector that bounces light down onto the canopy.
When planning a horizontal garden make sure you build in aisles and spaces between your rows of plants that will allow you to physically access the plants and all your equipment easily, and consider how you plan to hang the lights for even coverage.
Vertical gardens are better than horizontal gardens in some ways because they save space and increase yield per watt. But they require some unconventional equipment to set them up properly.
With a vertical garden, lights are positioned vertically and the plants are arranged around them. For example, you could build a tiered vertical shelf system several stories high in an octagon or hexagon shape around light that is mounted vertically in the center. Shelves could be tilted 45º so the plants are angled towards the light.
With a vertical garden hardly any light is wasted – all the rays from the bulbs directly hit the plants with no reflection needed. Also, just like skyscrapers in a city take advantage of tight spaces, you can house more plants per square foot by building upwards.