Mark four evenly spaced lines vertically down the large pipe. These will serve as guides for the holes you'll drill.
Measure 12 inches from one end and mark a line around the circumference of the pipe. For reference, mark this end of the pipe "DOWN" so you'll remember that this end should go down into the soil when assembling your salad tower.
Using the hole saw, drill one hole where a vertical line intersects with a horizontal line. Now drill a second hole directly opposite, again at the intersection of a vertical and horizontal line. (Mind you, these holes do not have to be perfectly aligned; just get them in the ballpark.)
Drill three more holes along the same vertical lines, leaving about 10 inches between holes. You now have two lines of four drilled holes.
Drill three holes on each of the remaining vertical lines, offsetting each new hole so that it's placed diagonally from those adjacent to it, making an alternating pattern.
To use in the garden: Use shovel to dig a 10-inch deep hole in the ground and bury the bottom end of the pipe almost to the first hole.
To use on a patio or balcony, drill several holes in the bottom of a 5-gallon bucket or large planter and fill halfway with gravel. Place the pipe on top of the gravel and add soil around the pipe, to the top of the container.
Drill about 30 randomly-placed quarter-inch holes in the 2-inch PVC.
Place small PVC pipe inside the larger PVC so that the top of the inner pipe is slightly higher than the outer pipe. (Add a bit of soil inside the 8-inch PVC to elevate the 2-inch pipe if necessary.) Once established, filling this inner pipe with water aids in getting moisture to the roots.
Fill the large pipe with potting soil up to the bottom of the lowest holes, keeping the inner pipe centered.
Fold a piece of cardboard into a V and set it inside the hole. Slide a seedling into each of the lowest holes, using the cardboard as a funnel of sorts. Gently push the piece of cardboard into the hole. This helps to prevent potting soil from escaping. Add more soil to reach the next set of holes. Lightly water seedlings in, to settle the soil. Continue in this manner until each hole is planted.
Add a few more plants in the top of the tower.
Water the tower slowly from the top as well as into the 2-inch pipe.
Harvest leafy greens as they mature.