Rhododendron is actually a group of cross-bred hybrids. They grow 4 to 6 feet tall in most cases, but can reach up to 10 feet in optimum circumstances. These large shrubs can overwinter where temperatures stay above minus-30 degrees Fahrenheit. Since rhododendrons are hybrids, they do not grow true from seed. You can propagate them, however, by rooting cuttings and taking tissue cultures. Cuttings offer a higher chance of success for breeding.
Take cuttings from an existing rhododendron from July to October. Look for medium-sized, healthy branches without flower buds. Measure 3 to 5 inches from the tip of the stem with a measuring and make a diagonal cut right below the bud with a sharp knife.
Fill a small pot with a mix of half peat and half perlite for each cutting. Prepare the cuttings by pulling off all but the top three leaves, and "wounding" two sides of each cutting. To wound, make diagonal cuts on the bottom of the cutting.
Dip the cuttings in rooting hormone. This will help them root more quickly. Push a cutting into each pot, pushing it 1/3 of its length into the potting medium.
Water the cuttings deeply. Place a stick in each pot that is slightly bigger than the cutting. Over that, put a plastic bag to increase humidity for the cuttings.
Observe the cuttings every few days, keeping the potting medium moist. After two or three weeks, the cutting should start to grow leaves of its own. At that time, remove the plastic bags and transplant the rooted cuttings to a larger container.