The amount of water a plant requires and uses depends on several factors, including plant species and structure; environmental conditions such as light, temperature and humidity; cultural conditions of the soil; and the type of container used.
Because rigid water scheduling may result in overwatering some plants, while allowing other plants to become excessively dry, you must be prepared to water plants on an individual basis depending on need.
There are several ways to determine when a plant needs water. Although some plants prefer their root systems to become slightly dry before their next watering, it's best to feel the soil on a regular basis and water before any wilting is visible. Other plants require even moisture and do not tolerate dry roots. These plants should be watered when the top layer of soil begins to feel dry.
The most convenient and efficient way to water plants is to pour water on the soil surface. Be sure to completely cover the surface of the soil with water so it does not simply drain down between the potting soil and the side of the pot. Plants don't tolerate waterlogged soil conditions, so don't allow them to stand in water. Plants kept indoors should be placed in saucers or trays to prevent water damage to floors and furniture. Apply just enough water to fill the tray, and discard any water that collects in the tray.
Generally speaking, it's better to water plants from the top than it is to subirrigate. Subirrigation is the process of watering plants by placing pots in a shallow amount of water in a tray or saucer, and allowing the soil to draw water up from the bottom via wicking action. It's acceptable to periodically water subirrigated plants to leach soluble salts from the potting soil.
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Updated Tuesday, July 22, 2014