Efficiency and the Indoor Garden

Your garden may be a functional producer—but if it’s costing you a fortune to keep it running, is it really worth it? So many gardeners look at the end result—the total yield of their crop—without looking back on what it cost to produce.

Take a 100 pound harvest of tomatoes, for example: if you are selling them for $2 a pound, your gross income would be $200. If it cost you $175 to grow that 100 pounds of tomatoes your net profit is only $25. By increasing your garden’s efficiency, however, you might be able to reduce your cost of production to only $100 and thus make a net profit of $100. The question should really be—how much profit margin do you want?

So, how do we make a really efficient indoor garden?

That is a simple question with a very complex answer—although efficiency begins with controlling your electrical usage, it also involves a symbiosis is of light, air movement and equipment.

So, from the ground up—let’s begin.

Painting the walls: it seems like a simple enough idea, but all too often this first critical step is overlooked. Of course if you plan on wrapping your entire garden in a thousand dollars or two worth of Mylar you can skip the painting—but I still don’t recommend it.

This is because paint does so many things for you: it seals the walls, ceiling and sometimes the floor; it prevents off-gassing from common building materials contaminating your produce; it acts as your primary light reflector, maximizing the dissipation of light throughout your garden; and it allows you to easily monitor the development of bugs, molds or other pathogens that like to hide on walls near your plants. Just remember that you don’t need to buy anything fancy—flat white is the best color and finish for the job.

When bringing electricity into your garden, copper is by far the best conductor available for supply wiring. Aluminum is about 40 per cent less conductive and about a third the cost, but for supply loads less than 100 amps the extra money for copper is worth every penny!

Remember that you are running equipment that uses a lot of power—cutting corners on safety or the use of underweight lines could lead to a devastating house fire.

Remote ballasts offer an advantage over attached ballasts as they can be placed outside the garden and only the wires needed to power the bulbs pass into the room, plus putting them outside the garden means that the heat they produce does not have to be offset by the garden’s climate control system.

Reflective hoods used to maximize the downward diffusion of light should be vented atmosphere-to-atmosphere. Vented hoods with fans of the appropriate size attached will carry most of the waste heat produced by your lights out of your garden and decrease the demand on your atmospheric control system.

But don’t stop there! For about $20 at your local home improvement store you can find sheets of polystyrene insulation that have been glued to reflective Mylar. Cut this insulation to sit on the tops of your hoods to maximize the ability of your venting system to carry heat out of your garden before it can escape back into your grow room.

Staggered crop lighting (SCL) is something that not too many indoor gardeners have heard about—and even fewer have actually taken the time to use. So what does SCL do? It simply allows you to light the same amount of garden space with half the power input. Some have claimed that there is an average 10 per cent overall loss in yield as a result of using SCL, but being able to save hundreds to thousands of dollars in electricity should be enough to compensate most growers for this loss.

SCL works by alternating the lights that are on every hour in a checkerboard pattern; this creates an effect on your plants similar to rolling clouds on a summer day. Turning on just half of your lights at any time means that half the amount of electricity is needed to power your garden—plus half the amount of cooling is needed for climate control and half the amount of infrared radiation is cooking your fragile leaves.

Climate control is the ultimate efficiency upgrade and key to making your garden productive: too warm or too cold and your yields will suffer—or you won’t produce anything at all. Heat rarely needs to be added (since lights provide so much), but cooling your garden is the secret to maintaining the perfect environment.

Two schools of thought exist when it comes to maintaining the proper garden environment: there are those who prefer atmospheric venting (AV)—or moving air from the outside through your garden using fans—and those who go with sealed gardening (SG), where the internal environment is controlled by air conditioners.

AV systems are less expensive to set up and operate than SG ones, but the supplemental CO2 that is necessary with an SG system usually produces such increases in yield that the additional cost seems insignificant.

If you go with the sealed gardening (SG) choice, you’ll also have to decide between a heat pump and air conditioning (AC). From a strictly energy efficiency point of view, the standard AC unit is your best option. This unit can operate year-round, but its use is limited to cooling only.

Heat pumps are designed to operate as both heating and cooling units, but unless your garden requires heating when your lights are off the extra cost is a waste. In either case, split units—or units that do not pass air from your garden to the outside—are recommended.

They are simple to set up and require only two hoses be installed from the exterior of your garden to the interior. Window AC units are generally not recommended as they are less efficient and they tend to pass air from inside your SG to the outside—and they are usually rather difficult to install where there is not already a window present.

The most important thing to remember when you are considering cost versus yield in your indoor garden is that every watt you put into your garden is a watt you have to pay for. From turning on the lights to cooling them down—everything adds up when you’re figuring out what your bottom line will look like after harvest.