How to Build a Modular Four Shelf Indoor Greenhouse

Introduction: How to Build a Modular Four Shelf Indoor Greenhouse

About: Vietnam era veteran (USAF), former air traffic controller, former entrepreneur, former clergy, former chauffeur. Currently retired and busier than ever. Devoted husband to an extremely talented wife and fathe…

The shelf system I've designed is constructed to hold four standard size (10" x 20") seed starting trays. The shelves themselves are each 25 inches long by 11 1/4 inches deep Since standard seed trays are 20 inches long and the posts of the shelving unit are 1 1/2 inches thick, the shelves need to be an absolute minimum of 24 inches long in order to easily slide the trays in and out. The unit is also designed to accommodate fluorescent lighting above each shelf which can be lowered and raised to keep the light close to the seedlings but allow it to be raised as the seedlings grow. In addition, the shelving unit is modular - the legs of each shelf are attached to the shelf, but they are held to the shelf below by dowels that are not glued. This way, the unit can be used as anything from a single shelf system through the full four shelf unit.


1 - 10 foot 1 x 12 (cut four 25 inch pieces) - about 18 bucks for standard grade

PLEASE NOTE: I got the wood for the shelves at a big box hardware store. A 1 x 12 is actually 11 1/4 inches wide. Depending on your wood source, a 1 x 12 could actually be 11 1/2 inches wide or even 12 inches wide. For the dimensions in this Instructable to work the shelves must be exactly 11 1/4 inches wide. Adjust accordingly.

7 - 8 foot 2 x 2s - between 20 and 60 bucks depending on grade (I recommend a higher grade for these for looks and straightness). As above, a 2 x 2 will actually be 1 1/2 x 1 1/2.

2 - four foot long 3/8 inch diameter dowels - about 2 bucks

5 yards of drawstring - 5 to 8 bucks

8 drawstring ends (usually sold in pairs) - 8 to 12 bucks

8 washers - 1/2 inch diameter with 1/4 inch hole

Stain and finish to taste

Wood filler

Carpenter's glue

4 - 24" light fixtures - about 50 bucks for the fixtures and another 20 to 40 for the bulbs


Table saw or miter saw

Drill with 3/8 inch brad point bit (see Figure 1)

Drill guide that has 3/8" guide (see Figure 2)


L square



Optional: Drill press

Step 1: Getting Started

STEP 1: Cut the 10 foot 1 x 12 into four 25 inch sections. Most big box hardware or lumber stores will do this for you. These will become the shelves. I used standard grade lumber to cut down the expense. If there are any knots or cracks in the wood, fill them with wood putty, let dry, then sand them smooth. Measure and mark 3/4 inches in from both long and short edges of each shelf in all four corners (see Figure 3). Carefully drill a 3/8" hole at each of these locations. If you have a drill press this will not be difficult. If not, use the drill guide to position your holes. It always help to drill a small starter hole with a small bit which will help you place the holes precisely. Be sure to use a brad point 3/8 inch drill bit when you drill the final holes as it will help your accuracy considerably. Getting all of these holes drilled centered on the mark and perpendicular is very important to the finished look and sturdiness of your project.

Step 2: Cutting and Bracing the Shelves

STEP 2: Cut eight 11 1/4 inch long pieces of 2 x 2 (Check this measurement against your shelves. Some 1 x 12 wood will actually be 11 1/4 inches wide, some will be 11 1/2. Cut these pieces to match the width of your shelves). I use these for bracing at the bottom sides of each shelf edge. Since I used standard grade wood for the shelves, this is important in order to keep the shelves from warping or bending on you and to straighten any bend that may already be there. Even if I had used a select grade of lumber for the shelves I would still have braced them like this. Measure and mark 3/4 inches in from the end of each 2 x 2 at both ends on one face. Measure and mark the center of the width of each 2 x 2 where it intersects the marks you just made. This will give you crosshairs at both ends of each 2 x 2 on one face. Use the dowel guide (or a drill press) and the 3/8 inch brad point drill bit to drill a 3/4 inch deep hole at each crosshair. In order to get the depth right, measure 3/4 of an inch from the end of the drill bit (not including the brad point) and wrap a piece of painter's tape around the bit there. Then when you drill your holes, stop when the painter's tape is flush with the wood. With the holes you drilled in the 2 x 2s facing away from the shelf, glue and clamp the 2 x 2 braces at each end of each shelf and let them dry. Note: Unless you bought some really good wood for the shelves, they will probably have a bit of a bow across the width. Glue the 2 x 2s to the shelves so that any high center of a bowed shelf is on the opposite side from the 2 x 2 braces. This will force the bow out of the shelf when you glue and clamp it. See Figure 4. When you're done, all four shelves should have a brace attached to each end, and each brace should have two dowel holes as in Figure 5.

Step 3: Inserting Dowels

STEP 3: Cut 32 pieces of 3/8 inch dowel, each 1 3/8 inches long. Put some carpenter's glue into each of the four holes in the top of each shelf and tap a dowel into each hole. You'll know you used enough glue if some of it oozes out when you tap the dowels into place. Wipe off any excess glue. Now turn the shelves over and glue and tap a dowel into each hole in the 2 x 2 braces.

Step 4: Making the Shelf Legs

STEP 4: Cut 16 pieces of 2 x 2, each 15 inches long. Cut another four pieces each 2 inches long. Cut two pieces of scrap wood 8 1/4 inches long and two pieces 22 inches long. Mark across both ends of twelve of the 15 inch pieces of 2 x 2 from one corner to the opposite corner to form an X on the ends of each piece as in Figure 6. The center of the X marks the center of each dowel hole. Mark just one end on the other four 15 inch pieces. Most drill presses cannot handle drilling into a piece of wood this long, so use the drill guide to drill a 3/4 inch deep 3/8 inch diameter hole in each marked end of the 15 inch pieces. See figure 7. Mark just one end of each 2 inch piece of 2 x 2 and drill a similar hole where you marked. Hint: I found it easier to do all this by clamping several of the 2 x 2s together side by side and using the drill guide to drill the holes one right after the other. This gives more surface area for positioning the drill guide than trying to drill each hole independently.

Step 5: Adding Legs to the Shelves

STEP 5: Do the following for three of the four shelves:

Turn the shelf upside down (braces up) and dry fit a 15 inch 2 x 2 that has holes drilled into both ends onto each of the four dowels projecting from the braces on the bottom of the shelf. Make sure the dowels aren't so long that they won't allow the pieces to join flush. If you encounter a dowel that is too long, sand or cut it down a bit until each leg fits flush to the brace. Turn the shelf with the legs dry fitted on the dowels over and fit the bottom holes in the legs onto the dowels of another shelf. Check to make sure none of the dowels are too long and adjust them as necessary like you did above. Now glue all four legs to the dowels on the braces Check to be sure everything is straight and true with the L square and adjust as necessary while the glue dries. Use the 8 1/4 and 22 inch pieces of scrap wood you cut for this step to insert between the legs to maintain proper spacing. Then use clamps to keep everything in place as you glue the legs into the braces. You can also tightly tie some string or rope around the outside of the legs with the scrap wood spacers in place to help keep the legs in the proper position. Note: At this point it would be wise to mark each shelf to remember which is which so that you can assemble the modules in the proper order. I suggest numbering them on the bottom of one of the legs - the end that does not get glued. Mark the same leg on each shelf so you can remember the order. You don't have to mark the bottom shelf, of course, because it will be the one with the 2 inch legs.

DO NOT glue the bottom of the legs into the shelf beneath them. What makes this shelving system modular is that the shelves are not glued to each other - they are simply joined by the dowels in the top of one shelf fitting into the holes in the bottom of the legs of the shelf above it so that the unit is stable and sturdy but can still be disassembled into separate shelves with legs. You have now built three shelves, each with legs 15 inches long as in Figure 8. Reward yourself!

Step 6: Adding Legs to the Bottom Shelf

STEP 6: For the fourth shelf, glue and clamp the four 2 inch pieces of 2 x 2 to the braces at the bottom of the shelf (after making sure the dowels aren't too long, of course - as in step 5). This will be the bottom-most shelf of the unit. You still have four 15 inch pieces of 2 x 2 that each have a hole drilled in just one end. These will be used as part of the assembly that will hold the fluorescent light fixture above the topmost shelf.

Step 7: Making the Assembly for the Topmost Fluorescent Light Fixture

STEP 7: I like to make things purely with wood and glue if I can - no nails or screws. But this next part may be difficult and a bit tricky to get everything flush, true and secure. For that reason, wherever I talk about drilling holes and using dowels from this point on, you may want to use glue and nails or glue and screws instead - it will be easier. If you do use nails or screws, countersink them and fill the holes with wood putty and sand them smooth. Nobody will be the wiser.

Mark each of the remaining four 2 x 2s at 13 1/8 inches up from the end with the hole. Use a protractor to mark a 45 degree angle from this mark upward toward the nearest end of the 2 x 2 (the end without a hole). Cut on this angle with a table saw or miter saw. On the newly cut face, measure and mark a line 1 1/2 inches up from the 13 1/8 inch side At this mark, make another line at a 90 degree angle to the cut face and cut with a table or miter saw. Figure 9 will show a piece properly marked and cut according to these directions.

You now have a 1 1/2 inch square on the angled face of each 2 x 2. Draw a line across each diagonal of these faces to make a crosshair on the center of this square. Use the 3/8 inch brad point bit to drill a hole 1/2 inch deep into each of these faces. Cut eight 7/8 inch dowels. Glue and clamp four of these dowels into the four holes you just cut.

Step 8: Making the Light Fixture Assembly Part 2

STEP 8: Cut four 3 1/8 inch pieces of 2 x 2. Mark diagonals across both ends of each piece to determine the center, then use the 3/8 inch bit to drill a 1/2 inch deep hole into each end of each piece. Join one end of each of these pieces to the dowel in the angled end of each piece from the previous step. Glue the remaining dowels into the holes at the other end of the pieces you just cut.

Cut two 7 inch long pieces of 2 x 2. Mark a line at 3 1/2 inches, then mark a parallel line 2 inches out from either side of the first mark. This gives you a four inch long marked segment centered on the piece. From each end of this four inch segment, use a protractor to mark a 45 degree angle outward toward the ends of this piece. Cut with a miter saw or table saw on this angle. As in step 7, mark a line at 1 1/2 inches up each of the newly cut faces to give you a 1 1/2 inch square marked on the angled face. Also as in step 7, mark a 90 degree angle from this square and cut. Figures 10 and 11 show you all of these pieces laid out together in case there is any confusion. Draw diagonals across each end of the angled faces and drill a 1/2 inch deep hole with the 3/8 inch bit. Glue a dowel protruding from the 3 1/8 inch pieces into each of the holes you just cut so that you have made two U shapes from each of these pieces and the short pieces attached to the longer legs. You can now insert the longer leg pieces into the dowels of your top shelf (do not glue to the shelf) and clamp everything in place to dry.

Step 9: Making the Light Fixture Assembly Part 3.

STEP 9: Cut one 22 inch piece of 2 x 2. Mark diagonals and drill a 1/2 inch deep hole with the 3/8 inch bit in both ends. Cut two 7/8 inch dowels and glue a dowel into the holes in both ends of this piece. On the last piece you cut for the two inverted Us you made in the previous step you marked a centerline. Draw a line at 90 degrees to the centerline that is 3/4 of an inch from either edge of the piece. Drill a 1/2 inch deep hole at the intersection of these lines. Glue the dowels at each end of the 22 inch piece into the holes you just cut. This will join the two U shaped pieces together. Clamp and let dry. Again if there is any confusion, study Figure 12 to see how your assembly should look.

Step 10: Staining/finishing

STEP 10: Stain/finish the unit as you desire with each shelf unit and the top light fixture assembly separate. Once everything is dry, assemble the entire unit. I used a dark walnut stain on mine. I can recommend Varathane Triple Thick Polyurethane Clear Satin for a finish coat. One coat is equivalent to three coats of other finishes, it produces a waterproof finish, it is self-leveling and will not run when applied to vertical surfaces. Brushes can be cleaned with soap and water. Apply two coats, sanding lightly between coats with 220 grit sandpaper. For the bottom surfaces of the shelves only one coat is really necessary.

Step 11: Getting Ready to Install the Light Fixtures

STEP 11: For the top three shelves (not the bottom shelf) do the following:

On both sides, measure halfway across the width of the shelf and 1 1/2 inches down. Drill a 1/4 inch diameter hole through the brace at this point. Do this on both sides for all three shelves.I don't know if all fluorescent light fixtures are standard, but there should be two holes about 1/4 inch in diameter in the top of your fixture. Mine were a couple of inches in from each end. Place one of your light fixtures on top of the brace that runs along the top of the assembly at the top of the shelving unit. Mark a spot on the brace that corresponds to the position of the two holes in your light fixture. Drill a 1/4 inch diameter hole straight down through the brace at both of these points.

Cut eight 20 inch long pieces of drawstring in the following manner: Roll a piece of transparent tape around the end of the drawstring, then roll another piece of tape around the string centered on twenty inches. Cut through the tape and string so that half of the tape is on one side of the cut and half on the other. Measure another twenty inches and repeat the process. Continue until you have cut eight pieces. On each piece, thread a washer. I used 1/2 inch washers with a 1/4 inch hole. Tie a knot at the end of the string - just one end - to keep the washer from sliding off. Now run the other end of the string up through one of the holes in the light fixture. The washer and knot should keep the end of the string from passing through the hole. If not, use a bigger washer. Do this with all eight strings on all four fixtures. Assemble the light fixtures.

Step 12: Installing the Lght Fixtures

STEP 12: For the top three shelves do the following: Set a light fixture on the bottom-most shelf. Run one drawstring through the hole in the brace of the shelf above it on one side (from inside to outside), then run the other string through the hole on the other side. Pull the string through the hole and thread one of the drawstring ends onto the drawstring. You can now pull the drawstrings to raise or lower the light fixture to any height above the shelf below and secure it in place by sliding the drawstring end to the brace. Do this for the other two shelves, installing a light to hang from the bottom of each shelf to light the shelf below it. For the fourth light, thread the drawstrings up through the holes in the topmost center brace and thread a drawstring end on each drawstring. Now you can adjust the light for the top shelf the same way as for the lower three shelves. Figure 13 shows the drawstring on one end holding up the light fixture above a lower shelf. Your project is finished!

Step 13: Final Notes

In the picture at the front of my Instructable, you'll see that I customized my shelf to sit at the bottom of a set of stairs in front of a window by making the bottom legs longer and a different length on the right and left sides. This is the beauty of DIY - you can adjust whatever you're making to the environment in which you'll be using it. While the unit is quite stable, I've elected to screw a couple of eye hooks into the window frame behind the unit and used cable zip-ties to loop around the rear posts and through the eye hooks. This will help ensure that our dogs and/or grandkids won't accidentally knock the unit over whilst chasing each other through the house.

Depending on the quality of wood you buy, it will cost around a hundred to a hundred and fifty dollars to make this unit - but half that cost or more will be for the fluorescent light fixtures and bulbs and the finished unit will look nicer and be sturdier and more versatile than anything you can buy pre-made. I chose double light fixtures primarily because they were on sale, but single light fixtures will provide plenty of light and cut the cost of bulbs in half. You don't really need the "grow light" type of bulbs - regular ones will cost less and work just as well. If you want, you can make a transparent wrap for the entire unit from clear plastic available at any fabric store. Hardware stores and garden shops sell trays for starting seedlings. These seem to come in standardized sizes of 10 by 10, 10 by 20 and 5 by 20 inches. All of these will fit nicely on the shelves. I recommend 10 by 20 trays, one for each shelf. Whichever way you go, buy four extra of the clear plastic 10 by 20 inch covers. Turn one upside down on each shelf to use as a drip catcher under each tray. When watering, I highly recommend sliding each tray out of the unit and carrying it to the sink to water. You could cut a 10 by 20 inch board to slide the tray onto and carry to the sink when watering since the trays are thin plastic and will flex with the weight of soil and water they will be carrying. As a matter of fact, you should have a board almost exactly this size left over from the ten foot 1 x 12 you cut to make the shelves. Water each tray at the sink, then after the water has been absorbed for a few minutes, lift the tray out of the drip catcher, drain the remaining water out of the drip catcher, place it back under the tray and return the tray to the shelf.

I hope you enjoyed my Instructable - I just recently discovered this site and hope to be adding more articles in the near future.

1 Person Made This Project!


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