The successful watering of pot plants can be reduced to the aim of maintaining a balance between air and moisture in the potting mixture, so that both are readily available to the plants' roots. The best way of ensuring this is to water the growing mixture to saturation, while making sure that the excess water drains away as quickly as possible. How, in practical terms is this best achieved?
Firstly, one should water so that the entire surface area of the potting mixture is wetted, and that enough water is applied, so that the excess drains out of the bottom of the pot into a receptacle, or preferably, is carried away by a collecting pipe. Secondly, the next watering should take place when the top 2-3cm (1in) of potting soil has dried out somewhat. Generally, this allows for the desired air/moisture balance.
This method is somewhat counter intuitive, especially as many people confuse it with "over watering". Over watering, is a situation whereby the soil or potting medium permanently lacks sufficient air. It is generally caused by very frequent but shallow watering, as opposed to the method just described.
Another advantage with less frequent, but deeper irrigation (watering to excess) is that it prevents the buildup of salts in the medium, which is a major, but often overlooked reason for poor results with container plants. Tap and irrigation water are becoming increasingly saline, particularly in dry climates, while dissolved fertilizers (which are mineral salts) add to the salt concentration of the potting soil. Watering to the point that the excess drains out of the pot, periodically leaches out the excess salts.
Which method is best for watering your container plants? Obviously, hand watering with a hose or canister is laborious and time wasting. In outdoor situations, especially in areas with hot, dry summers, where it may be necessary to water at least once a day, hand watering, while feasible for indoor plants, becomes unsustainable. Undoubtedly, installing a drip-irrigation system is the most efficient and effective way of watering the pot plants. Here are some guidelines to help you get the most from the system, bearing in mind that the aim with each watering is to wet the total surface area and the total volume of the growing mixture.
*Space the drippers close enough to each other so that the all the surface area is covered by the water that they emit. A distance of about 20mm (3/4in) is usually enough.
*Be aware of the different flow rates of the drippers. The flow rate is the amount of water emitted per unit of time, expressed in gallons per hour (GPH), or liters per hour. Common metric flow rates are 1, 2, 4, and 8 liters per hour, which is ¼, ½, 1, and 2 gallons per hour.
*Use drippers with low flow rates for shallow and small pots, and drippers with higher flow rates for the bigger and taller containers. The aim is arrive at a total flow rate for each pot that is proportional to its volume, relative to the other pots. So a container that has four times the volume of another container, should have drippers whose total emission, is four times greater per unit of time.
*Turn on the tap, and time how long it takes for the water to emerge. If the drippers have been placed evenly within each pot, and the flow rates are proportional, then water should start coming out of the bottom of the different containers, at almost the same time!
*Set the water timer appropriately, adding perhaps a minute of watering time, in order to leach out the salts.
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