Stem cuttings are ideal for propagation of rhododendrons. It is important that the cuttings be done correctly and at the right time of year or the stem will not root and be viable. Propagation takes some time, but when it is done correctly, you will have a new rhododendron to plant outdoors. Cuttings can take anywhere from six weeks or longer 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. I have found the steps below produce the best results.
- Prepare the planting medium. Use one part humus and one part course sand. Place in a container about 6 inches in diameter and at least 6 to 9 inches deep so that the plant has enough room to grow after it roots.
- Cut the stem from new growth from the current growing season. Use a pruning shears to cut a 4- to 6-inch stem from the growth tip. Remove the bottom leaves at least 1 inch up from the bottom of the stem.
- Use a sharp knife to make a small cut in the bark on each side of the stem at the bottom of the stem.
- Dip the bottom of the stem where the cuts were made in a rooting hormone. Any rooting agent from a nursery will work as long as it states that it can be used to promote root growth on semi-hardwood plants.
- Place the stem in the soil mixture 1 to 2 inches deep. Lightly pack the medium around the stem to hold it up. Water well.
- Place the two dowels in the medium, one on each side of the stem, but at the edge of the container. Place a plastic bag over the container and the dowels. This will make a greenhouse for rooting the plant stem. Place the container in a location with indirect sunlight. Keep the soil moist until the rhododendron roots, which can take six weeks or longer.
- Test the stem for roots after six weeks. Gently put up on the stem–if it moves easily, it has not rooted. Wait another six weeks before testing again and repeat until the stem does not move. Caution: Never pull hard enough to pull the stem out of the medium.
- Remove the plastic from the container after the roots have grown and taken hold.
Go to the American Rhododendron Society for more detailed information