Depending on the watering needs of the plants and trees that you have in your lawn, you may want to consider digging an irrigation ditch to insure proper hydration. Begin by carefully mapping out where your irrigation ditch will go. Mark the path of the ditch with spray paint or with rocks so that you will locate it correctly when you start digging.
Start digging at one end and work slowly and deliberately toward the other end. Make sure to dig to the proper depth before you move forward. Since your ditch will hold standing water, you must dig into the water table. You will know you have hit the water table when your trench begins filling with earth water. Measure the depth with a ruler and use the ruler along the way to make sure that you keep the depth consistent throughout your ditch.
As you move forward, you will experience some backfilling. From time to time check behind you and shovel out any soil that has backfilled your trench. Use the ruler to make sure you have restored it to the correct depth.
Depending on the length of your ditch, this can be a long and arduous task. Wear gloves to protect your hands and make sure to bend from the knees when lifting shovels full of dirt and rocks to protect your back. If this is a major project or if you are working with harder rocky soil, you can use a chain trencher or a back hoe. A special irrigation trencher actually cleans up after itself, thereby eliminating back filling.
Once you have finished, survey your irrigation ditch and make sure that you have eliminated all back filling. Clean up the area around the ditch and be prepared to let nature take its course.