Rhododendrons grow well in USDA hardiness zones 4 to 8, depending on the cultivar type. While rhododendrons can be purchased at a nursery, planting them from seeds saves money. Rhododendron seeds germinate best between January and March. The seeds need to be germinated properly indoors to ensure that they sprout and remain healthy. Rhododendron seeds require moisture and heat to help the germination process. Once the seeds reach 2 to 3 inches tall, the plants are ready to transplant into individual containers.
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Things you need
- Peat moss
- Milled sphagnum
- Seed-starting flats
- Clear cling film or container
- Florescent lights
- 3-inch containers
- Water-soluble acid fertiliser
Combine equal parts of sand, peat moss and perlite to make a well-drained soil. You need enough soil to fill the amount of seed-starting containers you plan to use; the Azalea Chapter of the American Rhododendron Society suggests planting 40 to 50 seeds in a 4-by-4-inch container. Place the soil into the containers. Alternately, fill the containers with moist milled sphagnum. Water the medium to moisten it.
Smooth the planting surface. Sprinkle the rhododendron seeds onto the surface of the potting medium. Space the seeds evenly apart and avoid crowding them. Do not cover the seeds with the potting medium. The seeds settle on the surface.
Spray the potting medium with water to keep it moist. Cover the container with clear plastic or a clear container top. Leave 1 1/2 inches between the planting medium and the container to allow room for the seedlings to sprout. Continue to mist the medium with water to keep it moist. Never allow the medium to dry out completely or become too soggy.
Place the container in a warm, sunny location with a temperature range between 21.1 and 23.8 degrees C, such as the windowsill. Place the seeds under a fluorescent light for 16 hours each day if the windowsill does not provide enough light and warmth. Keep the light 8 inches above the seeds. Allow the seeds to grow until they are 2 to 3 inches tall, which can take up to three months.
Transplant the seedlings once they are 2 inches high. Separate the seedlings and thin out the weak ones. Place them into individual 3-inch containers with a fresh potting soil that contains an equal amount of peat moss and perlite. Continue to water the seedlings to keep the potting medium moist.
Place the seedlings outdoors when the weather warms. Place them in the shade away from direct sunlight. Leave them outdoors for an hour the first day and then gradually acclimate the seedlings to the weather to harden them. The seedlings need at least 16 hours of warmth per day, at a temperature of around 21.1 degrees C.
Fertilise the seedlings with a water-soluble acid fertiliser at one-third the strength. Follow the instructions on the fertiliser to ensure that you use it properly. Fertilise the seedlings every other watering for best results. Stop fertilising the rhododendrons in July to prepare them for the winter.
Tips and warnings
- Apply a fungicide to the seedlings if you notice fungus while they germinate. Follow the directions on the fungicide to use it properly.
- Sterilise the soil to reduce the need for fungicide by filling a large cooking pot halfway with water. Bring the water to a boil. Add the soil mixture and boil it for 2 to 3 minutes. Drain the soil into a mesh colander or cheesecloth-lined colander to remove the excess moisture.
- Use sand that does not contain limestone because rhododendrons do not grow well in salty or sweet soil.
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- Fearing's Farm Nursery; Rhodies 101: How to Start Rhododendron Seeds; Harold W. Fearing; November 2009
- American Rhododendron Society; How to Grow Rhododendrons from Seed; Allan Anderson et al.;
- Thomas Jefferson High School for Science and Technology; Raising Rhododendrons and Azaleas from Seed; Donald W. Hyatt
- University of Minnesota Extension; Azaleas and Rhododendrons for Minnesota; Michael Zins; 2009
- The Azalea Chapter of the American Rhododendron Society; The Easy Way to Germinate Rhododendron and Azalea Seed and Grow Seedlings; Frank Pelurie
- Fraser South Rhododendron Society; Rhododendron Basics; Harold E. Greer