How to Build a Potting Box for a Greenhouse
Learn how to make a potting box, or soil box, in the heart of a greenhouse.
For the best results, place the greenhouse so that the long side faces south and gets at least six hours of sunlight. Dig a trench the same size as the perimeter of the greenhouse 6" deep to accommodate the 4” x 6” timbers. Fill the trench with crushed limestone and tamp it down. Cut the timbers to length and put them on top of the aggregate around the perimeter of the base. Make sure timbers are level. Square the timbers by measuring corner to corner and then anchor them in with rebar. Pre-drill holes in the ends of the timbers and secure with 12" spikes.
Remove all the grass inside of the timbers, leveling the ground as you go. Lay the paver blocks flush with the top of the base of the timbers. Cut any off-sized pavers with a splitter. Dump sand over the floor and sweep it into the cracks.
Working from the inside of the greenhouse, attach the bottom plate to the corner struts and the wall struts to the bottom plate. The corner struts attach to the roof gable with a corner plate. Use two bolts in the corner wall struts and two in the roof gable. Put two additional bolts in the center wall struts. These will be used to connect the braces and door header. Slide on four bolts for the roof gable and attach them to the corner strut with an angle plate and then tighten the nuts. Tighten the bolts enough to hold them in place. Assemble the other end wall in the same manner but without a door frame.
Lay out the wall struts and attach to the bottom sill of the greenhouse. The two side walls are assembled in the same manner.
The end wall pieces have a channel, and this is where the side wall slides in. To attach the corners, loosen the four nuts on the plate that connects the end wall to the roof gable. Spread this connection apart in order to slide in the side-wall section, then bolt the bottom braces together. Do this in each of the four corners.
To attach the ridge pole, which runs from end gable to end gable, just loosen the bracket, slide it in and tighten it up. Attach the six roof struts by lining them up with the wall struts and bolting them in.
Assemble the frames for the doors and windows and secure them with screws. Attach the lock and handle to the door.
Slide the gaskets on the top and bottom of the polycarbonate panels before applying the silicone. Run short beads of silicone along the edge of the frame, install the frame and secure it with the provided spring clips. Once a panel is in place, there is another vinyl gasket that goes along the side of each panel. Snap it into place between the frame and the polycarbonate.
Make sure the greenhouse frame is sitting squarely and evenly on the base before screwing it down. To fasten, pre-drill and then drive deck screws through the bottom sill of the greenhouse into the timber.
Slip the panels into place and measure the gaskets to the proper length. Press the gasket all the way down and into place. Bow and flex the side-wall panels into place. After the side walls are in, press side gaskets into place. With the side panels and gaskets in, it's time to put one roof panel in place and then slide the strut down on top of it. The windows should just slide into place.
Attach the hinges to the door frame and then slide the door into place. The top of the greenhouse wall is the gutter system. To have the water drain away from the greenhouse, install the included downspout.
Use a utility knife to cut a hole in the polycarbonate panel on the back wall of the greenhouse. Install the louver on the outside of the greenhouse. Mount the fan with the motor on the inside using carriage bolts.