Making sturdy, adjustable greenhouse shelving does not require heavy construction and an array of professional tools. Dependable shelves in a design that maximises the space of a gardener's greenhouse configuration requires only good measurements, the right timber, a saw and a few concrete blocks. Plan to use the height of the greenhouse by building three tiers of shelves in a step or amphitheatre design. This shelving configuration maximises space and is still accessible to the gardener of average height.
Measure the interior sides of the greenhouse with a metal tape measure and note the measurements on a notepad.
Calculate the amount of wood needed to construct the three tiers of shelves on three sides of the greenhouse interior. Plan to construct shelves with a surface area width of 60 to 90 cm (2 to 3 feet) with space between the surface boards to provide for runoff and expansion/contraction.
Buy cypress boards if using wood, as cypress easily withstands constant humidity. Boards measuring 5 cm (2 inches) thick by 10 to 20 cm (4 to 8 inches) wide by 2.4 m (8 feet) long are heavy enough to keep them from warping. Purchase concrete block for supports. Plan to lay the concrete block on its face so that each block measures 60 cm (2 feet) long by 30 cm (1 foot) high to provide the most stability. Purchase enough concrete block to support each of the three tiers of shelves at the chosen heights on each end and at 90 cm to 1.2 m (3 to 4 foot) intervals to keep the board from sagging over time.
Borrow, rent or purchase a table saw or skill saw to cut the cypress boards for the surface of the shelves if the boards require shortening. Double-check the measurements for the shelf surfaces, adjust the guide attached to the table saw, and ask a friend to hold the far end of the boards as the gardener pushes the board along the guide and into the cutting blade. To use a skill saw, set the boards on two sawhorses set far enough apart to support both ends. Allow the end of the board to be cut to hang off one of the sawhorses. Mark the cut to be made with a carpenter's pencil and guide the saw blade along the pencil mark. Make all the necessary cuts and place the cut boards in the greenhouse.
Stack the concrete block for the tallest shelf up the three walls to be shelved. Stack blocks for the ends of the shelves and for the supports at the appropriate points along the mid-length. Lay the cut cypress boards atop the blocks.
Stack more concrete blocks in front of the first blocks, stopping 60 cm (2 feet) short of the first blocks. Lay cut cypress boards atop this next lower tier of blocks to form the second tier of shelves.
Repeat the stacking process once more for the third and lowest tier of shelves.