Seed Starting Shelf

Author Photo
By Tom Larson | Mar 1, 2008

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Cutting diagram for plywood
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For years, I made unsuccessful attempts to start tomatoes and peppers from seed. Each time the seeds sprouted nicely and appeared to be off to a good start. But, as the safe time to harden off the plants approached, they were usually spindly and weak. When it was time to set them out, I’d make another trip to the garden center to buy tomato and pepper plants.

Persistent as I am, a year or two later, I’d try again, each time thinking that I had found some better way. I had the required sunny south window, so inadequate light didn’t strike me as the problem until I noticed that in March (when I planted the seeds), sunlight bathed my seedlings, but as the sun climbed higher in the sky, the patch of light grew smaller and smaller until the overhang on the south side of the house blocked it entirely.

Based on this observation, I decided I needed a different approach to providing light for the seedlings, so I built a shelf system using inexpensive, fluorescent shop lights. I had the system ready to use in the spring of 2000, and I’ve used it with good results each year since. In planning the system, I included a lower section as a place to over-winter herbs in pots. After a winter under lights, rosemary, basil, sage, thyme and oregano look a bit bedraggled, but after a few weeks outside in the spring, they thrive again.

Material List

• 3 12-foot 2-by-2s
• 2 10-foot 2-by-2s
• 1 8-foot 2-by-2
• 1 12-foot 1-by-2
• 6 10-foot 1-by-2s
• 4 4-by-8-foot sheets 3/16 inch (5.2mm) luan plywood
• 40 3-inch deck screws to fasten together 2-by-2 box frame
• 40 2-inch deck screws to fasten together shelf frames
• 210 No. 6 3/4-inch screws to fasten plywood to framing
• 20 No. 8 3/4-inch pan head screws to fasten lights to framing (if not using chain)
• 20 1-inch cup hooks to fasten lights to framing (if using chain)
• 30 (or 20) pieces shelf brackets; 6 per shelf for 5 shelves (4 per shelf, 5 shelves)
• 6 (or 4) pieces shelf support 6 feet long
• 12 linear feet of 4-foot-wide Mylar (optional)
• 10 4-foot, 2-tube fluorescent lights (see discussion of materials)
• 20 cool white fluorescent tubes (see discussion of materials)
• 1 timer
• 1 10-outlet plug strip or 2 6-outlet strips
• 4 (or 6) medium-duty casters (optional)

Construction notes

Extension service experts indicate that one light is sufficient for two standard 11-by-21-inch flats. However, if you intend to use most of the surface area of the shelves, two lights are required to provide the recommended 25-30 watts per square foot.

Different types of fluorescent tubes can be used. The sources I consulted recommend ordinary cool white tubes or a combination of one cool white and one daylight tube in each shop light fixture. Experts generally agree that the so-called grow lights or plant lights don’t produce appreciably better results and are more costly.

Although the older magnetic ballast fluorescent fixture often can be had for very little money, they are expensive to operate and relatively heavy. I recommend only the newer electronic-ballasted types because they are lighter in weight and use much less electricity.

New-style fixtures can be fitted with either T12 (40 watt) or the newer T8 (32 watt) tubes. T8 tubes provide about the same amount of light as T12 tubes with a saving of 8 watts per tube and, in my experience, there’s no noticeable difference in results. Because I was unable to locate T8 lights for this project, I used T12s that cost less than $9 each.

Lights can be affixed to the shelves with supplied chains or they can be screwed directly to the underside of the top frame and shelf frames. Fastening lights directly to the frames provides more usable vertical space, but requires that the shelves be moved more often to maintain the correct distance between the lights and plants.

No matter how you fasten them, buy the fixtures before you begin because the location of the top frame and shelf frame pieces will be determined by the points where the lights are meant to be suspended from chains or screwed to the frame.

To get the most of your light energy, you want the back of your unit to be as reflective as possible. Finding no expert advice detailing the use of Mylar, aluminum foil or other reflective material, I chose Mylar because it is long-lasting, easy to use and simple to install.

The number of shelves in your unit will depend on the maximum height of your plants before you move them to another location. The instructions and materials list are for five shelves; feel free to adjust this number to suit your needs.

Four or six shelf support strips can be used, depending on how heavily you plan to load the shelves. Heavily loaded shelves with six supports will require six casters on the base, one at each corner and two in the center. Using six casters requires that all the casters swivel, which I prefer, whether using four or six casters.

Nominal 2-by-2 lumber is now actually 1 1/2 by 1 1/2 inches or 1 3/8 by 1 3/8 inches in cross section. Nominal 1-by-2 lumber is actually ¾ by 11/2 inches or ¾ by 1 3/8 inches in cross section. The instructions for this project are for

1 3/8-by-1 3/8-inch and ¾-by-1 3/8-inch material; measurements and notes for using 11/2-by-11/2-inch and ¾-by-1 1/2-inch material are in parentheses.

Use the photographs and cutting diagrams that follow, along with the written instructions, to guide you through the construction. Pilot holes should be used for all screws except those used to fasten the shelf strips to the frame.

If you intend to move the shelf system through doorways, up or down stairs or the like, make sure there is enough clearance. The system is 6 feet 3 inches high, 5 feet 3/8 inch wide and 1 foot 73/16 inches deep. Add the height of casters, if you use them.

Step 1 With the frame pieces cut to length – six 2-by-2 721/4-inch (72-inch) uprights, four 2-by-2 60-inch horizontals, eight 2-by-2 165/8-inch (163/8-inch) braces, and two 2-by-2 277/8-inch (275/8-inch) bottom reinforcement stringers – mark the centers of the horizontals where they will be fastened to the center uprights.

Step 2 Drive 3-inch screws through the horizontals into the ends of the six uprights.

Step 3 Drive 3-inch screws through the horizontals into the ends of six braces.

Step 4 Mark the centers of the three lower braces. Fasten one stringer in front of the center marks and the other behind the center marks.

Step 5 (Not shown.) Using one No. 6 3/4-inch pan head screw every 6 inches, fasten shelf support strips at the center of the two inside uprights and near the inside corner of the four outer uprights.

Step 6 Measure the distance from the end of one of the shop light fixtures to the point where the chains are to be attached – 11/2 inches for the lights I used for this system.

Step 7 Add 6 inches to this measurement (11/2 inches plus 6 inches equals 71/2 inches). Make a mark at this distance from the ends of each of the upper horizontal pieces. Mark the centers of the ends of the remaining two braces. Center the ends of the braces on the marks and fasten them with 3-inch screws.

Step 8 The completed frame.

Step 9 Tape Mylar to the frame before adding the plywood.

Step 10 Using the cutting diagrams on Page 71, make the first cut in three 4-by-8-foot sheets of 3/16-inch plywood. You will have three 48-by-75-inch
pieces and three 21-by-48-inch pieces.

From two of the larger pieces, cut the two 30-by-75-inch back pieces and fasten them to the back of the frame with No. 6 3/4-inch screws, one every 6 inches and about 3/4 inch from the edges of the plywood. (Save the two 18-by-75-inch pieces for shelves.)

From the remaining 48-by-75-inch piece, cut the two 195/8-by-75-inch side pieces and fasten them to the sides of the frame in the same manner.

Cut two of the remaining 21-by-48-inch pieces into two 195/8-by-303/16-inch top pieces. Fasten these to the top of the frame. (Two pieces of plywood are used for the top and bottom to minimize waste.)

Step 11 Cut the third 21-by-48-inch piece down to 30 by 197/16 inches, and another 30-by-197/16-inch piece from the remaining whole sheet of plywood (these are the bottom pieces). Saw notches 13/8 by 13/8 inches (11/2 by 11/2 inches) from the four outside corners and 7/8 by 13/8 inches (3/4 by 11/2 inches) from the inside corners.

Step 12 Fasten the notched plywood pieces to the bottom frame with No. 6 3/4-inch screws.

Step 13 Cut five 10-foot 1-by-2s into 10 591/2-inch shelf frame sides, two for each shelf. Mark them 71/2 inches from the ends. Cut 10 141/2-inch 1-by-2 braces from the remaining stock, two for each shelf. Mark the centers of the edges of the braces.

Step 14 Assemble the shelf frames using 2-inch screws to fasten the braces centered on the 71/2-inch marks on the shelf frame sides.

Step 15 (Not shown.) Cut a 591/2-by-48-inch piece from the remains of the fourth sheet of plywood. Make two lines that divide this piece into three 16-inch shelves. Cut on these two lines with the saw blade (kerf) centered on the lines. (The deviation from a 16-inch width is insignificant and makes economical use of plywood.) From the two 18-by-75-inch pieces left over in Step 10, saw two more shelves 16 by 59½ inches.

Step 16 (Previous page.) Screw the five shelves to their frames using No. 6 3/4-inch screws.

Step 17 Mark the 141/2-inch frame pieces at 4 inches from the edge of the shelves. Drill pilot holes for the No. 8 3/4-inch screws that will be used to fasten the lights to the frames or for the cup hooks from which the chains will be hung. Also, drill pilot holes for cup hooks in the underside of the upper 2-by-2 frame pieces.

Step 18 With a good exterior white paint, coat the bottoms (not the edges yet) of the shelves. Screw the cup hooks or screws into the holes made in Step 17. Rotate the shelves by the cup hooks or screws and unpainted edges so they rest on the cup hooks or screws. Then paint the tops and edges. Also, paint the inside of the bottom. Once the paint is dry, attach casters if you are using them.

Step 19 Assemble the lights (if assembly is required) and, using the supplied chains, hang them from the cup hooks. Or, remove the screws that were used temporarily to support the shelves while painting, and use these screws to fasten the lights directly to the shelf frames. If you’re using hanging lights install them before mounting the shelves. If your fixtures are direct mount, install them after the shelves are in place.

To install the shelves, insert 6 shelf clips at the desired position along the shelf support strips and set the shelf on top of them.

Note that there are no lights hung from the underside of the bottom shelf. When plants are small, the upper shelves will be close together near the top.

Without this extra shelf, the plants at the lowest level would have to be on the bottom, and the lights suspended with long chains and tending the plants on the bottom would be inconvenient. As the plants grow, the shelves will be spaced farther apart, and the lowest shelf can be removed.

Tom Larson, of Sioux Falls, South Dakota, is an avid gardener and woodworker and combines those passions whenever possible. Lathe-turned bowls and vases, and beautiful organic produce are among his specialties.

Andy: Do this like “Fit for a Wren”, where the text goes with the images. There are two steps (5 and 15) without images, please include them with the previous step, i.e., step 4 and step 5 both go with the step 4 image.

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