Before laying the line, check to see that the trench pitches evenly toward the intended low spot. Laying a length of rigid pipe in the trench before measuring with a 4-foot level gives a more accurate reading. The trench should slope just slightly.
My next step was to determine what kinds of connections I needed and where they would go. First I had to figure out where the low point in the system would be. That’s where it would all drain. My garden is downhill from the house, with a drop in elevation of almost 30 feet, which would allow gravity to drain the system. Because the land slopes to the center of the garden, I decided to install a drain valve there, along with a spigot, from which I could water the whole fenced kitchen garden (C on site plan). I also wanted a spigot outside the garden on the uphill side (B), so I could run a hose and sprinkler to my pumpkin patch and perennial beds. Finally, I needed a third spigot at the far end of the line (D) that, when opened, would let air in and cause the line to drain completely. All three of these connections would be housed in wooden boxes set in the ground, which would give me quick access to them. In addition, I’d need a few elbow connections because, although irrigation line is flexible enough to curve gently, it can’t make sharp turns.
After I had a basic plan, I took it to a plumbing supply store that specializes in irrigation systems to make sure I had everything covered. They looked at my plan and said it was fine. I bought 1-inch PVC irrigation line, and standard PVC plumbing fittings for all the connections.
With these decisions behind me, it was time for the real work to begin.