Propagation of geraniums by cuttings is a fast way to produce many plants inexpensively. The new plants are identical to the mother, so choosing a healthy and vigorous mother plant is essential. Rooting plants hydroponically is similar to normal rooting conditions, but plants are placed into hydroponic growing medium rather than soil. When using commercial rooting materials, you will need to adjust the water for pH as recommended by the manufacturer. Use plain distilled water if rooting in sand.
Remove the mother plant from the nutrient solution two to three days in advance. Water it heavily with water under the same pH and moisture conditions that you had been maintaining it with hydroponically.
Choose a growing medium. Rapid Rooters, Rockwool or Oasis cubes are effective, but clean sand works well also.
Cut several holes in the bottom of a plastic cup, a few small holes will do the trick. Pre-soak the growing medium in distilled water and place it in the plastic cup. Punch a hole in the growing medium using a small twig or pencil.
Prepare the rooting hormone according to package directions. Use rubbing alcohol to clean your hands, the craft knife and the scrap wood.
Back the stem with the scrap wood and slice cleanly through the stem using the knife. Choose a growing stem, approximately 3 inches long, with at least one leaf, two or more is best. Cut approximately 1/4 inch below a leaf node at a 45- to 60-degree angle. Cut off the leaves at the stem, using the knife, leaving only the leaves at the tip.
Place the cutting into the prepared rooting hormone according to package directions, then poke it into the hole in the growing medium. Bury one-half to two-thirds of the stem in the growing medium. Push the growing medium around the stem to support it.
Put the cuttings in a domed seed tray and mist them with water from the spray bottle. Mist the inside of the clear dome and place the dome on the tray. Repeat the misting two or three times a day.
Place the dome in filtered sunlight or under grow lights. Monitor the temperature under the dome and do not allow it to get too hot. Ideal temperature is between 72 and 80 degrees F.
Water the cuttings with plain distilled water every other day. In very dry environments, water daily. Keep the growing medium moist, but not wet.
Check the plants after a week by removing the dome and leaving it off for an hour or so. If the plants begin to wilt, mist and replace the dome. If the plants do not wilt, leave the dome off and stop misting but continue to water, keeping the plants moist.
Move the plants to the hydroponic system when the cuttings are completely rooted, approximately two weeks after taking the cutting and begin watering with nutrient solution.