While some plants must have soil in order to form roots, others can be rooted in water. Plain tap water can be used for rooting, but it must be regularly changed to keep the water clean. Placing the plant in a spot where it receives light without direct sunlight will allow the plant to root most effectively. There are a few popular indoor and outdoor house plants that will do well with water rooting.
The leaves of African violets root well in plain water. A dark-colored container should be used. This will keep the stem of the leaf, or petiole, from being exposed to light. If it is exposed, the stem will curl in the light's direction. The dark container should be filled three-fourths of the way to the top and covered with aluminum foil. The petiole should be trimmed so that it will barely touch the water and pushed through the foil so that it rests with the leaf above the foil. The water will have to be checked regularly to ensure that the stem is still touching the water. Check the roots every few days and don’t let them grow much longer than half an inch in the water. Once they have rooted, they must be moved into a pot with soil.
It is possible to root a coleus plant in water by using a stem of the plant. The stem should be cut from the bottom of the plant and the leaves must be removed before using it for rooting. Rooting a coleus can be accomplished in the same way as African violets, by placing them in a dark container with just the tip of the stem in the water. Coleus roots can grow a few inches before they must be potted. They root quickly though, so they must be checked often. It is possible that the roots will rot before planted if they are not regularly checked for health.
To root Impatiens, place 3- to 6-inch cuttings from an impatiens stem into a glass of water and place on the windowsill. Like coleus, impatiens can root quickly. Once a 1- or 2-inch root has formed, move the plant to a pot with soil to prevent the root from rotting. Liquid root stimulator can be added to the water to help the roots form.