Container gardening is all about giving the pot plants optimal growing conditions. While everyone knows that plants have to have access to sufficient moisture, it is less obvious, but no less essential that there be a ready supply of oxygen in the root zone. Understanding the air/moisture balance is probably the key to successful container gardening; but while the hydroponics method achieves this for indoor plants, outdoor pot plants have to have some sort of drainage system. The question is then, what type of drainage is best?
The most common method is to place some receptacle underneath the pot, which collects the excess water flowing out of the bottom. Such an arrangement hardly deserves the epitaph – “system”. It may be the most obvious thing to do, but it is far from being the best.
The main problem is water spilling over and staining the floor or pavement, which induces people to water using small quantities on each occasion. The correct method of irrigating container plants is to water to excess, and then wait until the top 4-5 cm of potting mixture have dried out to some extent.
The aim is to arrive at a better air/moisture ratio in the pot, while periodically leaching salts from the medium. In other words, worries about soiling the pavement lead to irrigation practices that are detrimental to healthy plant growth and development.
After years of growing container plants outdoors in a dry climate, where regular and automatic irrigation is the prerequisite for success, it is clear to me that the simple receptacle method is inadequate. A far better idea, although one not without its own drawbacks, is to attach each pot to a common pipe that takes the excess water to a drainage hole on the roof or patio, or out into the garden soil.
This means that in addition to a feeder pipe bringing water to the pots, there is a collector, or drainage pipe taking water away. While the irrigation pipe is usually 16mm in diameter, the drainage pipe should be 20mm in diameter. The pot is carefully drilled on its side, so that a connecter can be inserted in the hole and then attached to the 20mm drainage pipe. If the container contains drainage holes on the bottom, these obviously have to be sealed with material like epoxy putty or silicon.
The method is perfect in terms of providing optimal growing conditions for the pot plants, because it allows for correct irrigation and proper drainage, without fear of spillage and staining. The disadvantage though, is aesthetic, as it is not always easy to disguise the pipes and the connectors. The work is also laborious and painstaking, if future leaks are to be avoided. For this reason, it is not a cheap option if passed on to a hired professional.