With their waxy evergreen leaves in fall and winter, and big, showy blooms in spring and summer, rhododendrons are stunning plants year-round. Although taking a stem cutting is the best way to propagate a rhododendron, propagating a rhodie is challenging and unpredictable because cuttings can take anywhere from six weeks to a year to take root. If you're patient, chances are good that eventually a cutting will root, and the results will be well worth the effort. Take a cutting from a healthy rhododendron between July and September.
Water the parent rhododendron the day before you intend to take the cutting so the plant will be well-hydrated. Take the cutting in the morning, before the heat of the day.
Clean the pruning shears and knife before you take the cuttings. This can be done by wiping the shears with rubbing alcohol or a mixture of nine parts water to one part bleach.
Cut 2 to 4 inches off the tip of a healthy branch, and cut off the lower leaves. Leave the upper leaves, but cut them in half crossways. Smaller leaves will help the cutting to take up water and nutrients more efficiently, and will take up less space in the pot.
Make a ½- to 1-inch cut lengthwise in the bottom of the stem, and then dip the stem in rooting hormone. Plant the stem in a planting container filled with potting soil, but don't allow the leaves to come in contact with the soil. Plant several cuttings in the same pot, but don't allow the leaves to touch.
Mist the soil with a spray bottle, and put the container in a clear plastic bag. Bend a piece of wire in a hoop shape and insert it in the soil to keep the plastic from coming in contact with the rhododendron cutting, then seal the bag.
Put the container in a warm spot. If you have a heat mat, put the container on the mat to keep the soil about 65 degrees Fahrenheit. Although a mat isn't essential, it will speed up the process, and will increase the chance of success. Mist the soil if it appears to be getting dry, but never soak it, because excess moisture will invite rot or disease.
Put the container in a well-lit place, but don't put it in a windowsill, or in direct sunlight. The sun will be magnified through the plastic, and can scorch the cutting.
Remove the cutting from the plastic as soon as the rhododendron cutting has rooted This can be determined by pulling gently on the cutting, and if you feel resistance, the cutting has taken root.
Put the container back in indirect light, and continue to keep the soil damp. Plant the new rhododendron outdoors in March or April of the next year, after all danger of frost has passed.