Subterranean Irrigation System

Watering and water savings made simple. This is a irrigation system I designed to take advantage of the IFusion Watering Spikes. The system is gravity fed and slowly delivers water directly into the soil for the plant roots to drink up when they need it. Everything but the watering spikes are available at a hardware store and this basic concept is expandable and can be easily customized to your own garden and green space.

IFusion Watering Spikes (Container or Outdoor)

1/2" PVC pipe, schedule 20 or schedule 40

1/2" PVC female threaded outlet tee (1 per watering spike)

1/2" PVC 90 deg elbow, female thread-slip fitting (2 per irrigation unit)

1/2" CPVC adapter, male thread-slip fitting (1 per watering spike)

3/16" hose barb adapter with 1/2" male thread (1 for reservoir + 2 per irrigation unit)

1/2" Hydroseal Gasket (1 for reservoir)

1/2" PVC riser pipe, 4" long (1 for reservoir)

1/2" PVC threaded coupler (1 for reservoir)

Container between 1 to 5 gallons (1 for reservoir)

3/16" ID vinyl tubing

Tools: Saw, PVC cement, All-purpose PVC-CPVC cement, thread sealing tape, drill, 1-1/4" hole saw, adjustable wrench.

Determine where watering spikes are desired. For this Instructable, I am doing a regular spacing of 18" between three watering spikes, but different spacing and number of spikes are possible. To get a correct pipe length for the irrigation unit, subtract 3/4" (0.75") from the spacing distance. For an 18" spacing this would be 17.25". A 12" spacing would be 11.25" and 24" spacing would be 23.25".

Glue the pipes you cut in Step 1 with the tee fittings. To the best of your ability, make sure the 'tee' portion of the fittings are all facing the same direction. This makes it easier to push the finished unit into the soil.

Cut two more pipe 1.75" long. Glue one into each 90 degree elbow fitting and then glue the remaining pipe stub into the end tee of the irrigation unit. Be sure to point the elbow in the opposite direction of the 'tee' of the irrigation unit.

Wrap thread tape (or some other sealant) around the threads of the hose barb adapter and add to the threaded side of the elbow.

For each tee in the irrigation unit (this example has three), prepare a watering spike by gluing it into a CPVC adapter with male threads. Place a line of glue around the outside near the open end of the spike, inserting into the fitting, then giving it a twist to make certain there is a good seal.

Wrap the threads with thread tape and screw a watering spike into each 'tee' of the irrigation unit. The irrigation unit should now be complete.

Using a 1-1/4" (1.25") hole saw, drill a hole toward the bottom of the container making sure the Hydroseal gasket will be able to make complete contact on the outside of the container. Insert the Hydroseal gasket so the flange is in contact with the containers outside surface. Insert the 4" PVC riser pipe into the hole in the Hydroseal gasket so that the threads on both ends of the riser pipe are not in contact with the gasket. Place thread sealing tape on the threads of a riser pipe and a 3/16" hose barb adapter. Join those two pieces using a PVC threaded coupler.

Use of the riser pipe is advantageous because of the threads on both ends. This allows for different connections that may be more suitable for you garden needs (valves, tees, water meters, ect.). Having an available connection on the interior allows a siphon tube or filter to be easily attached.

The complete system is easily connected with 3/16" ID tubing from the hose barb on the reservoir to one of the hose barbs on the irrigation unit. A second run of tubing is added on the opposite hose barb and is secured back at the reservoir higher than water level inside the reservoir. The second run of tubing is useful to help purge air, flush the system if needed, or connect multiple irrigation units together (daisy chain) where only the tubing on the last unit is secured near the reservoir.

The irrigation unit is setup by pushing the watering spikes into the soil. The reservoir is placed 1 to 3 ft above the watering spikes.

A good starting estimate for water usage is one spike will use one gallon of water in one month. A lot of factors can affect this number such as rainfall and the water demanded by the plants. The watering spike works by keeping the soil damp rather than flooding it, so plants drawing out the water will force more water out of the spike.

The irrigation unit shown in this Instructable is the middle unit and this system has two additional units of 2 spikes each at 24" apart. This bed as 4'x4' and located in the basement with six 100 watt daylight LEDs.