2.2.2 Micro-Irrigation: Container Production

Aboveground Container or Pot-in-Pot Production

Several irrigation methods can be used.

For containers in greenhouse systems, a capillary mat subirrigation system works for small containers on level gound or on benches with a solid flooor. The capillary mat acts as a wick to move water and nutrients. Subirrigation means applying water with trickle emitters to a porous pad under the bottom of containers. The water and nutrients move up into the container by capillary action. Excess water evaporates or drains away.

Capillary mat systems could be replaced with a flood system ( ebb and flow system) that circulates water and nutrients to the plants, allows them to drain, and repeats again at regular intervals. A pump floods the floor and then water drains back into a tank.

Individual emitters or spray stakes of one type or another are also good for watering containers (see Container Emitters diagram).

A ¾ in. polyethylene supply pipe runs lengthwise down the rows of containers. Small diameter tubes are inserted into the pipe and have a spray stake or emitter at the other end. The spray stake or emitter is inserted into the container and distributes water over the container surface. Spray stakes spread the water over more surface area for more even wetting in larger pots.

Larger, wider-spaced containers (e.g. in pot-in-pot systems) are prime candidates for applying trickle irrigation in place of overhead sprinklers. Usually, the ratio of container surface area to total ground area is smaller and the water savings greater for wider-spaced containers.

Installing and keeping trickle irrigation emitters in small containers outdoors is more difficult than indoors. Animals, wind, or people moving among the containers knock emitters out.

Longer-term (perennial) crops are better candidates for trickle because of the labor involved in removing and setting up the small tubes and emitter devices in the containers. While there are potential problems, water and nutrients are more efficiently controlled.

The pot-in-pot arrangement has pots sunken into the ground to provide support for plants in their growing containers. The in-ground containers keep the growing containers upright. The irrigation lateral, in this case, is buried with the emitter and emission (supply) tube fastened to the side of the in-ground pot. When a new plant container is placed into the one in the ground, the emitter is placed in the growing container.

Container watering is more efficient when water is applied at least twice a day (cyclic irrigation) to keep adequate moisture in the growing substrate. Some growing substrates may not wet evenly if allowed to dry out between irrigations. The plants are less moisture-stressed by frequent waterings.

Some ongoing studies suggest better substrate wetting using slow application rates to allow the water to spread laterally through the substrate.