You can propagate using seeds but it's slow and will take a couple of years to stabilize. Cuttings would be your best bet for propagation. The best time to take a cutting is in the Spring. When the plant has fresh vigor and puts out new leaves in the Spring is the best time for taking cuttings off rhododendron or azalea.
- Select a healthy rhododendron plant
- Take a 6-inch cutting from a side shoot in spring or early summer.
- Remove the bottom leaves
- Dip the cut end in rooting hormone
- Fill a pot with a well-draining potting mix
- Insert the cutting 1–2 inches deep
- Cover the pot with plastic wrap or place it in a mini greenhouse to create humidity
- Place the pot in a warm, shady spot
- Water regularly and monitor the soil moisture
- After about four weeks, the cutting should have roots and can be transplanted
How to root rhododendron cuttings in water
Take a cutting: In the summer, take a non-woody side shoot from a one-year-old rhododendron.
Prepare the cutting: Make a right-angled cut below a leaf node, and remove a strip of bark from above the cut.
Submerge the cutting: Place the cutting in water so that at least one leaf node is submerged.
Change the water: Regularly change the water to promote healthy roots.
Provide light and warmth: Place the cutting in an area with bright, indirect light and a warmer temperature.
Wait for roots: Roots should appear in 3–4 weeks, but it can take longer.
I use pure RO "reverse osmosis" or fresh rainwater for all my cuttings.
Good luck friend and if you need any help just let me know I will be glad to help if I can.
Transplant: When the roots are 1–2 inches long, transplant the cutting into a pot.