This is the best option for an inconspicuous system because all supply pipe is safely underground. Subsurface irrigation systems will last longer and should be considered the only truly permanent drip irrigation system. On the other hand, burying pipe means you’ll have to investigate local codes, do a great deal of trenching, and spend longer doing the installation.
The installation of subsurface supply lines is similar to that for sprinkler systems. You need to make the same decisions in determining which valves you need, grouping them in manifolds, staking, and trenching. Drip irrigation systems can share the same manifolds as sprinkler systems and the same controllers, as long as they are on separate circuits and have a pressure regulator. Although the two may be watering different sectors of the yard at different pressures, they are all part of the same system. Either poly or PVC pipe can be used from the water connection to the head of the circuit.
Be aware that although a pressure regulator is not used in most sprinkler systems, it is essential to drip irrigation. Its purpose and installation are described in Surface Drip Installation. It should be placed as the last element of the manifold, at a rate of one regulator per circuit.
Emitters are usually set aboveground, even in subsurface drip irrigation. Only porous hose and treated emitter line are ever fully buried. Subsurface supply lines are set 8 to 12 inches deep. This means the supply line will have to be brought to the surface level again to join the header. To do this, use an elbow joint and a piece of PVC pipe or poly pipe acting as a riser.
With subsurface installation, 1-inch or 3/4-inch PVC or poly pipe is commonly used for all underground sections up to the header lines, which are usually made of 1/2-inch poly pipe (sometimes PVC pipe). Use a reducing fitting to join the two sections. Finish by flushing well.