Now that most of the houseplants that were once part of the patio landscape are now back indoors as part of the interiorscape, or at least in transition from the outdoors to the indoors, a change in methods for watering are in order.

When growing outdoors in full sun and periodic windy conditions, there is a tremendously strong “pull” on the water in the plants from the atmosphere.  Plant physiology textbooks call this influence matric potential or water potential depending on the situation.  Evapotranspiration is a term that we use when referring to these forces in turfgrass portions of the outdoor landscape.   All 3 of these descriptions help us understand the draw that the atmosphere places on plants, causing the liquids inside the plants to be pulled upwards and out of the plant, requiring that it be replaced, sometimes on a daily basis.  Keeping the soil moist, not soggy or dry, is the goal for patio planters and houseplants outdoors.

Once these plants have been moved indoors, the forces are greatly reduced.  Why?  Indoors, there is much less light intensity, much reduced wind speed and overall slower growth rates.  As a result, the water usage rate is also greatly reduced.  In order to water indoors to match the differing conditions, 4 guiding principles are in order:

1. Realize that greatly reduced frequency of water applications will be required.
2. More houseplants are killed by overwatering than underwatering.
3. Just as for outdoor plants in the middle of summer, aim to keep the soil moist, not soggy or dry.
4. Sticking a finger or a popsicle stick into the soil in a pot will help determine just how moist it is at any given time.

For the most part, applying water at the top of the soil, moving the water spout around the soil surface to distribute it evenly and stopping when the entire soil volume is filled and water is visible exiting the drainage holes in the bottom of the pot is the desired routine to follow.  A good rule of thumb is that about 10 to 15 percent of the water that is applied should drain out in order to completely fill all of the voids or air spaces in the potting soil.  Some veteran houseplant growers use an old cake pan or oil change reservoir to catch that water that has drained out and use it to moisten their other plants.

John Fech

Horticulture Extension Educator at Nebraska Extension

John Fech is a horticulturist with the University of Nebraska-Lincoln and certified arborist with the International Society of Arboriculture. The author of 2 books and over 200 popular and trade journal articles, he focuses his time on teaching effective landscape maintenance techniques, water conservation, diagnosing turf and ornamental problems and encouraging effective bilingual communication in the green industry. He works extensively with the media to extend the message of landscape sustainability, making over 100 television and radio appearances each year.