How to Build a Small Wood Grow Box Step by Step

Ever wondered if it was possible to build your own grow box? Grow boxes are excellent spaces for plants, giving them the optimal conditions for plant growth. They’re perfect if you live in small spaces like apartments, and can even be cheaper alternatives to those sold by manufacturers.  

1. Setting up your basic frame

Before you begin hunting for materials to build your grow box, it is important to plan its 3D design. You can use Google’s free program, Sketchup, which allows you to create a 3D model of the grow box. The program comes with a measuring tool to ensure your box is designed up to scale. 

Here is the list of materials needed:

  • Two sheets of medium-density fibreboards (MDF), 4′ x8′ x 1/2″ 
  • Seven pieces of MDF, 2″ x 2″ x 8′
  • All-purpose screws, 2.5”
  • Wood screws, #10 x 1.25” 
  • 3M spray glue 
  • Mylar sheets 
  • Power adapter
  • Chicken wire
  • Caulk Saver
  • Activated carbon
  • Two CFL lightbulbs
  • One MH and HPS lightbulb
  • Power strip
  • Two adapters 
  • Zip ties
  • Four caster wheels
  • 16 fasteners – nuts, washers (1.4” each) and bolts

Caster wheels and fasteners are optional but may prove to be handy if you incorporate them into your grow box. Print out a copy of the Sketchup template, and use it as a guide on where to make cuts to the fibreboards. 

Here are the final measurements of the MDF panels:

  • Two front panels – 1’11” x 4’11” 
  • Two side panels – 2’ x 5’
  • One top and one bottom panel – 2’ x 1’11”

For the 2” x 2” pieces, you may request for them to be cut, according to the following:

  • 1’8” (19”) x 12
  • 5” (60”) x 4

For the assembly of the base – ensure that two 2” x 2” panels are exactly level with each other. Leave a gap of half an inch for the other two panels, so that the front and back panels can be placed on them. Refer to your Sketchup template for clarity.

Next, attach the second crosspiece about one foot away from the top. You may adjust the length between the crosspiece and the top, according to the amount of space you want to have for the lighting. 

Next, combine two frame panels together, and attach them to the base of the box.

2. Enclosing the grow box

If you wish to attach wheels, you may do so before continuing to the following steps. You may flip to the underside of the caster, using it as a guide for drilling holes. Insert the fasteners. 

Attach some mylar sheets to them, spraying some spray glue on the surface before laying the sheets as evenly as possible. Then, attach the side pieces to the box using the wood screws. 

3. Setting up ventilation in the light chamber

To set up fans for the ventilation of your grow box, go for smaller ones. A rough guide of the size would be something around 80 x 80 x 25mm. You can use computer fans, which work great for this project.

Place two in the grow chamber, and one for the lighting. Based on these specifications, the air will be continuously replaced every 18 seconds in the grow chamber and every nine seconds in the light chamber. 

Cut two holes into the side panels using a 1” hole saw drill bit, to insert the fans. Connect them to a power adapter, so that you can avoid a blowup of the fans. Rewire the cables by cutting the tips and entwine them to that of the fans with an RCA cable. Wrap the wires in the insulating tape and connect the fans to the adapter.

Place one fan for fresh air intake in the bottom corner of the back panel, and the exhaust fan in the top corner of the front panel. Separate the light and grow chamber with an attached glass.

Glass panels can be purchased from any hardware store. Non-tempered ones cost less and opt for pieces that are around ⅛” thick. 

4. Setting up lighting 

For the light chamber, we’ll be using a metal halide (MH) and a high-pressure sodium (HPS) light. Use the screws to attach the bulb fixtures to the top panel. MH bulbs are suitable as a primary source of light and give off a balanced spectrum for plant growth at all stages. HPS bulbs are great for boosting plant growth, and provides orange light (close to the afternoon light spectrum).

5. Setting up the ventilation and air filter

Here, you’ll be setting up the air ventilation for the growth chamber. The chicken wire will be used for the air filter. To calculate the length of the wire, multiply the diameter of the cylinder by the value of 𝝿. Using zip ties, fix the wire in a cylindrical shape. Place the activated carbon in it, and secure it with a thin cloth. 

Once this is done, cut a length of Caulk Saver that’s enough to go around the bottom of the filter. This fixes the central wire in place. Cap the PVC joint to the cylinders and use duct tape to secure it in place. Ensure there are no air spaces so that the air will flow through the carbon only. 

Next, attach the ends of the PVC joint to the intake end of the fans. This allows the air to be suctioned out of the filter, with the exhaust channeled out of the box. 

With the fans attached, place the filter inside the grow chamber, such that it doesn’t block the light at the top. You may do so by aligning it alongside the side panel. 

Now, to fix the air filter to the box, cut holes for the fans to fit into the side panels. Cut out the first hole, then position the filter and the fan to find a suitable position for the next hole. Make some markings on the panel before cutting the second hole. 

Position the wires to stick outwards of the holes, and wire them the same way you did for the fans in step three.

Use duct tape to secure the wires, and to keep the holes airtight. Secure duct tape around the filter, as well as on the inside, to ensure that none of the unfiltered air leaks out of the grow chamber. Wrap duct tape to where the fans connect with the PVC as well. 

You may also use zip ties to create a harness to hold the other end of the filter and hang it onto a hook secured to the opposite panel. This will minimize the strain placed on the fans attached to the PVC. For additional support, you may also attach some wood beneath the fans, using screws to hold it in place. You may also add screws to the panels, in case you want to adjust the position of the power strips.

6. Setting up lighting in the growth chamber

The next step is to install 100-watt compact fluorescent lamps (CFL) for the grow chamber. These will only be used in the initial stages of plant growth. 

Attach two of the power strips onto opposite panels, using zip ties to secure the bulbs to the strips. You may wish to place higher spectrum bulbs at the top, and bulbs of lower spectrum slightly lower on the opposite panel – giving a wide range of light for the plants.

7. Assembling everything together 

To start running the fans, you just need to connect the RCA cable to a power supply. To bring down the voltage of electricity, opt for a two-pronged power supply.

Next, you’ll want to attach the leads of the exhaust and air intake fans to that of the power supply. Simply cut away the connectors of the power supply and attach them together. See that the fans are turning in the correct direction, and wrap the connected leads with duct tape. 

If the fans don’t seem to be running at complete capacity, then you may consider connecting them to their own power supplies. 

Finally, for the platform of the grow box, make one that is six inches shorter than the base. Next, cover the remaining base with a black plastic sheet, for light absorption. Staple and use duct tape to secure the sheet to the panel on the right side. On the left side, secure the sheet with screws, making it removable when you want to check on the grow box. Once the fan runs, the lifting of the plastic will indicate that air is being blown inside. 

Constructing a grow box can be a challenging yet fun project for those who are interested in hydroponics. The total cost amounts to less than $400, which is cheaper than some sold on the market. With this basic grow box, you are also free to install additional items to boost the growth of your plants. Happy plant growing!

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