January 6, 2011 at 8:42 a.m.
According to Deb, watering plants when you think about it or on a regular basis according to the calendar, are both wrong. It's important to water them before wilting, but it's a mistake to keep soil wet all the time because it just encourages root rot. Room temperature and humidity, even how sunny or cloudy the weather has been, affect the plant's water requirements.
Learn to read the signs when your plants need water. The foliage will turn slightly duller with a less lively green. Succulent leaves become a little rubbery. The container feels lighter as moisture evaporates from the soil and soil feels dry to the touch, first at the surface, then below it. Water requirements vary among different groups of houseplants, but regardless of the type, water them thoroughly each time you water, and spill off extra water that comes through drain holes.
Cacti and succulents may be allowed to get quite dry between waterings, though when light is good, they'll thrive on additional moisture. Plants with leathery leaves such as the old-fashioned rubber tree or ponytail palm can also go a long time between thorough waterings.
The type of potting soil can also have an impact on how often you water, as well as the type of container. Always use clean, fresh potting soil that has different sized particles. Varied particle size results in good soil drainage. The more moisture you wish the potting soil to retain, the higher peat content there should be.
Layering pebbles or charcoal in the bottom of a solid container will not help soil drainage. Choose containers with drain holes so water can drain freely from the soil. Be sure to spill out any excess water that remains in the tray or saucer after a few minutes. If the container is too large to lift easily off the tray, use a plastic turkey baster to siphon most of the extra water.
Don't use softened water unless you don't have a choice, because it adds chemical salts to the soil that will eventually injure the roots. Chlorine, which is added to city water to purify it for drinking, is not present in large enough amounts to damage houseplants. Fluorine, added to fight tooth decay, may be a different story. Plants with long, pointed leaves such as dracaenas and spider plants are quite sensitive and can develop brown tips. However, most plants have no problem with city water.