Pelargoniums, commonly called geraniums, are perennial plants that grow year-round in U.S. Department of Agriculture plant hardiness zones 9 through 11. In other climates, you can grow them as annuals or as houseplants. Garden centers and nurseries usually have a wide selection of these plants in the spring, but you can grow your own geraniums from cuttings taken from the plants already growing in your garden. Take cuttings in late summer.
Mix together equal amounts of course builder’s sand, perlite, peat or vermiculite. Any combination of two of these ingredients is fine. Rinse the sand with water until it runs clear before using it. Pour the mixture into pots. Use pots with drain holes that are at least 2 inches wide by 3 inches deep. Moisten the medium with water.
Cut 4- to 6-inch-long pieces from the ends of stems, using sharp scissors or pruners. Remove the blooms and buds from the stems and snip the leaves off the lower half.
Use a pencil or screwdriver to poke 1-inch-deep holes in the rooting mixture. Space multiple holes far enough apart in the container to prevent the cuttings from shading each other. Pour a small amount of rooting hormone powder into a small cup. Coat the bottom 1/2 inch of the cutting in rooting hormone. Insert the bottom end of the cutting into the planting hole and press the soil firmly around it. Water the newly planted cuttings to settle the soil.
Place the container in a clear, 1-gallon zip-top bag and seal it or set multiple containers in an old aquarium with a piece of glass or plastic on top. Alternately, cut the bottom out of a plastic soda bottle or milk jug and set it over the container.
Set the cuttings in front of a north- or east-facing window or next to a south- or west-facing window in a warm room. Soil temperatures between 72 and 75 degrees Fahrenheit are best. Water the pots only when the soil becomes dry. Remove the covering for two to three hours if condensation forms.
Pot the cuttings up separately in a soil-based potting soil when they have developed root systems with 1/2- to 1-inch-long roots. This usually takes about one month. Plant them in 4-inch pots at the same depth they were growing previously. Water them immediately after planting.
Water the new geraniums as often as necessary to keep the soil lightly moist. Give them a 20-20-20 or 15-30-15 water-soluble houseplant fertilizer one to two weeks after transplanting. Dilute the fertilizer at a rate of 1/2 teaspoon per 1 gallon of water or at one-half the rate recommended by the manufacturer. Fertilize every two to four weeks.
Set the geraniums next to an east-, west- or south-facing window. Move them in front of the east-facing window for brief periods, gradually increasing the length of exposure to direct morning sun. Hang a sheer curtain in front of a west- or south-facing window and gradually increase the amount of time the geraniums spend directly in front of the window. Bright but cool direct sunlight is best.