Incorrectly watering indoor plants accounts for a large percentage of house plant losses. The most common question gardeners ask is, "How often should I water my plants?" There is not a simple answer to this question. There are several basic points to consider:
  • Plants with large or very thin leaves and those with fine surface roots usually require more frequent watering.
  • Plants in a warm, dry, sunny location need more frequent watering .
  • A large plant in a small pot will need water more often.
  • Flowering plants and rapidly growing plants dry out quickly.
  • Different soil mixes require different watering schedules.
  • Water evaporates quicker from the sides of a clay pot than from plastic pots.
  • Not all plants need the same amount of moisture; some like to dry out between waterings, others need to be kept moist.

Forgetfulness is a common watering problem. When you forget to water, the soil drys out and the roots are damaged from dehydration and fertilizer burn. Never allow the plant to wilt. A lack of water can result in dwarfing, leaf spotting, and leaf drop. When a potting soil containing peat moss gets dry, it may be difficult to remoisten. The water may run down the side of the pot instead of wetting the soil. The best solution is to develop a habit of checking the plant on a regular schedule.

Water thoroughly every time you water a plant. Apply enough water to moisten the entire soil volume, plus a little extra to leach soluble salts out of the container. Indoor plants are usually placed in saucers to hold excess water that drains from the bottom of the pot. If the plant is left standing in this water, the moisture will be reabsorbed into the pot. This results in root rot, salt injury, and generally poor plant performance. To prevent the problem, discard any water in the saucer after each watering, or elevate the base of the container above the level of drainage water. One way to do this is to spread a layer of gravel in the bottom of the saucer deep enough to keep the bottom of the container out of the water.

The feel and color of the soil should be used as a guide in watering indoor plants. Plant roots are usually in the bottom 2/3 of the pot. For most plants, do not water until the bottom 2/3 starts to dry out slightly. You can't tell this by looking, so you have to feel the soil. When the top 1/2 inch of the soil (in containers up to 8 to10 inches in diameter) feels dry, the plant probably needs watering. For a 6 inch pot, stick your index finger about 2 inches into the soil (approximately to the second joint of your finger). For smaller pots, 1 inch into the soil is the proper depth to measure. Commercial plantscapers use small water adsorbant sticks poked in the soil to detect the amount of soil moisture. You might try using a porous toothpick. If the soil feels damp, don't water.

Plants differ in their preference for soil moisture levels. Some prefer to be kept moist but not wet. They must have a relatively uniform amount of water in the soil at all times. These plants tend to have a fine root system that will die if the soil becomes very dry. Others prefer to dry out between waterings (top 2 inches of soil). Finally, there are some plants with coarse roots that are well adapted to dry conditions.

Water should be at room temperature. This is especially true for tropical plants. Water on the foliage of African violets will cause water spots if the temperature of the water is more than 15°F cooler than the leaf surface. The best time to water is in the morning.
Cacti and succulents can go without water for a long period. Many interior plants that are not given artificial light go into a resting stage during the short cool days of winter. During this season watering should be reduced.

Moisture meters are available to determine the amount of water in the soil, but they are not reliable. The amount of fertilizer in the soil will influence the reading. If you fertilize heavily, the meters tend to read that the soil is moist even when the soil is dry.

For small plants you can tell when to water by picking the pot up. Water weighs more then air, so a dry potted plant will be lighter than one that has recently been watered.

Tap water is acceptable for watering most plants. Some plants are susceptible to fluoride injury from treated water. Many susceptible plants have long slender leaves such as dracaena and spider plant. Injury is characterized by brown spots along the margin or leaf tip. Fluoridated water should be allowed to sit at room temperature over night before using. Potting soils containing perlite can also cause fluoride injury. Softened water should not be used since it contains sodium that can increase the soluble salt levels in the soil.

 


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© Erv Evans, Consumer Horticulturalist
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