Watering is a key factor in the successful growth of houseplants. Surprisingly, overwatering is more often a problem than underwatering in hampering this growth. Most plants are growing little if at all; consequently they need no fertilizer and need less water than they needed when they were growing vigorously. Too much water applied too often means the soil will stay saturated for long periods, causing the roots imbedded in the waterlogged soil to begin to rot and die. With their roots gone, plants wilt as if they're parched; as a result these plants won't perk up when they're watered. If the soil is kept saturated with water, it contains no air so the roots can't function and eventually rot.
Some plants are exceptionally susceptible to damages cause by overwatering. These plants include: cacti, which are essentially dormant in the winter and succulents, which need to dry out between thorough waterings. However, even plants that generally prefer moist soil can get too much water and suffer damage.
Using pots with drainage holes in the bottom is the first step in avoiding watering problems. The holes allow excess water to drain out of the soil; the excess water should be discarded so it isn't absorbed back into the soil.
There are a variety of watering methods, all of which have an effect on the amount of water the plant receives. Water may be poured in on top of the potting mix or the pot set in water, watering from below; both of these are popular methods that will work with most plants. There are some plants affected more drastically by the watering method than others - cyclamen and African violets are sensitive to water in their crowns and on their leaves and fare better when watered from below. When watering from above, the water should be added until some comes out the drainage hole. If the potting medium has dried and pulled away from the sides of the container, the water will run straight through without moistening it. When this happens, leave the container sitting in water until the soil surface is moist, then discard the remaining water as in watering from below.
When determining the watering needs of houseplants, it is important to take cues from the plants themselves. If the potting mix feels bone-dry and has shrunken in the pot, it needs water. Dry media are lighter colored than moist soil mixes and more light weight. A wilted, flabby plant most likely needs water; however this also can occur in a plant that is wilted because of overwatering, when the roots are rotted away and the plant can't take up water anymore. The most reliable way to check for dryness involves feeling the potting medium. If the surface is dry, feel a little deeper. The decision of watering should be based upon the watering needs of the particular plant.
"Watering Is Often the Key to Houseplant Success" by Lee Taylor Extension Horticulture Specialist Michigan State University MSU Cooperative Extension Service