Propagate rhododendron cuttings as a hardwood. The woody stem produced during the end of the growing season on plants and shrubs is referred to as hardwood. Hardwood is somewhat pliable but will generally snap when bent in two. Although hardwood cuttings require more time to cultivate, it is worth the effort to grow a duplicate of the beautiful flowering rhododendron used as the host plant. Cuttings from the smaller rhododendron taken root more easily than those of the larger varieties.
Select upright stems instead of side shoots from which to gather the rhododendron cuttings. Check the stems for freshness by bending them at a 90-degree angle. If a stem breaks, it is not suitable for use. Cut 6- to 8- inch pieces off the ends of the stems at a 45 degree angle. Cut the tops of the cuttings straight across to differentiate between the bottoms.
Fill the growing pot with a planting medium and moisten slightly with a spray bottle filled with water. Do not over-saturate the soil. Soggy soil causes the cuttings to rot and discourages rooting. Using a pencil or your finger, make uniform holes 3 to 4 inches deep in the soil.
Remove the bottom leaves of the rhododendron cuttings but leave the top 2 or 3 to allow for photosynthesis to occur. Rinse off any dirt or debris. Check that the bottom leaf nodes are not damaged. Using a razor blade or utility knife, strip the outer bark off the lower half inch of the cutting, leaving the leaf nodes on the rhododendron cutting.
Pour 2 to 3 tablespoons of rooting hormone into a separate container. This keeps the master container of hormone powder free from any bacteria. Dip the rhododendron cuttings into the small container of rooting hormone and stick in the holes made in the planting medium. Tamp down the soil, removing any air pockets that may contain bacteria.
Cover the entire pot with the plastic bag and seal with a rubber band. If the bag touches the cuttings, prop it up with pencils or bamboo skewers. Place another rubber band around the bag at the top of the pot to keep moisture around the cuttings and not around the pot.
Place the cuttings in a sunny location away from direct sunlight. The heat generated by the sun kills delicate cuttings. Monitor the cuttings to keep the soil moist and to remove any dead cuttings or those infected with mold. It may take two months or more for the cuttings to produce roots.
Watch for signs of new growth. This signifies root growth. Ensure the roots have formed by gently tugging on the cuttings. Resistance means roots have grown. Remove the plastic and keep watering as necessary until a healthy root system forms. Transplant the new plants into separate growing containers until the weather warms up.
Harden off the new plants by taking them outside during the day when temperatures reach 60 degrees. Once the nighttime temperature remains in the 60's, transplant the new rhododendron plants in the flower bed.