Raising plants from seeds is the simplest propagation method. But for rhododendrons, you can propagate them through vegetative means due to the natural variation that occurs from the use of ovules. The usual vegetative way is cuttings. You use small stems from the parent plant, and under controlled conditions, they grow into a new plant. Others are grafting and layering.
Propagation Through Seeds
Growing rhododendrons from seeds are not tricky but depending on the type, it can take 18 months- 5 years for the first flowers to open. You may get seeds from other plants that have pollinated naturally or buy. Harvesting seeds from the plants when the pods ripen, burst, and scatter them. To make work easier, tie a small paper bag over the ripening pods to hold the seeds when they burst open.
Sow the seeds in finely sieved potting mix. The mix should contain a 50/50 mixture of sphagnum moss and peat/bark based. Please don’t cover the seeds; leave them on the surface and gently moist them. Keep them lightly shaded. They will take ten days, six weeks to germinate.
The best moment to sow seeds is during spring to make sure the plants are healthy over the winter. The seeds are very tiny and will only do well when in controlled conditions. Provide the following;
- Temperatures of about 18 degrees Celsius
- High humidity
- Diluted liquid feeding
Transplant them after forming the first real leaves into other containers. The seedlings should stay in the flats for around two years before transferring them to the open ground.
Use of Cuttings
Take the cuttings in early fall from new growth that is beginning to harden -off. Softer woods are the best and roots faster but are more prone to fungal diseases. The stems also wilt quickly under the slightest moisture stress. Harvest the cuttings in the morning when the moisture content is high and water the plant before cutting the branch when it’s not raining to keep it hydrated.
Prepare a sanitizing solution with a one-part-bleach to 10 parts water. The solution sanitizes the tools and containers that you are going to use on the cutting. Wipe the plastic container’s interior and add an equal amount of peat and moss with warm water to create a crumby rooting mixture.
Choose the items that are growing upward and have a terminal bud. Avoid the branches at the top that have turned brown as they will fail to root. Sanitize your shears and then cut 2.5 -3 inches long cutting. Remove four to six leaves near the tip of your cutting and cut-off to half all the remaining leaves.
Cut two- 1-inch marks near the bottom of the cutting to create wounds that will encourage root growth. The scars should be deep to expose the inner wood of the cutting. Place the cutting into a sanitizing solution for 2-3 seconds, then drain it on a sheet of paper.
Check this too: How to Save a Dying Rhododendron
Dip the cutting into a rooting hormone; a thin layer should cling to the cutting and cover the wounds. The hormone and the woods make rooting faster. Make a hole in the rooting substrate and place your cutting. Cover around the cutting and the pot with clear plastic paper to maintain humidity. Place the vessel in an area with good light and not direct sunlight with temperatures around 70 degrees F. Cuttings take 2-4 months to root. Remove any cutting showing any signs of dying, mold, or infections. When roots develop, transplant it to another container outdoor for further growth.
When preparing many cuttings, you need to repeat this procedure for each cutting. To increase the rooting rate of the cutting, cut it between July and October when the growth hormone mature. Also, treat your cutting with fungicide solution after dipping it in a sanitizing solution.
The fungicide protects the cutting from fungal infections. Additionally, making wounds on the stem exposes the cambium layer, which speeds up the rooting process. Transplant the cutting into a sterile mix of 60% sphagnum peat moss and 40% perlite. Again, fertilize them once a month.
Cutting Methods for Various Rhododendrons
- For evergreen azaleas with small-leafed alpine, take softwood cuttings from spring to fall, cuttings prepared during fall roots faster than those in spring. First cuttings root more quickly in 6-8 weeks under mist and 12 weeks or more without moisture.
- Broad -leafed species, take a semi-ripe cutting from early summer to mid-fall and ensure you mist them to avoid wilting. Stems taken in mid-summer have flower buds, and you should remove them to preserve the cutting food resource.
- Deciduous types are challenging to grow in cutting and mostly needs special care to establish before winter.
Layering Method
It’s the best way to propagate the plants that are difficult to root in cuttings. But the method is slow and may take up to 2 years to show results. Low- growing plants like evergreen azaleas often self-layering where the stems touch the ground. You can cut these layers and replant them elsewhere. You can still stimulate natural layering by keeping a branch in contact with the soil to form roots.
Select a pliable stem that you can bend to the ground level. Dig out a shallow trench where the branch touches the ground, make a shallow cut on the twig’s underside, and apply a rooting hormone to the wound. Using wire or wooden hoops, peg down the stem into the trench. Support the growing tip with a bamboo cane to ensure it’s upright, then refill the trench.
Aerial Layering
Select a firm stem that has a green bark. Remove the foliage from the stem and make a shallow upward cut. Lift the flap of the bark and wedge into it with a sharp stick. Lightly dust the wound with a rooting hormone powder and wrap the area with wet sphagnum moss.
Later wrap the ball of sphagnum in black polythene and secure it with tapes. The moss keeps the wound from drying and promotes rooting at the injury. The method takes 10-12 months to produce roots. You can transfer the cutting after radicles develop into a vessel.
Grafting Propagation
The advantage of grafting is that you choose disease resistant and soil tolerant rootstocks. The best time to graft is early in spring before new foliage expands. Grafting requires the cambium of the stock, and scion kept in contact for them to fuse. The process involves trimming and fitting to get a good match for compatible plants. Saddle and side wedge graft methods are the most commonly used.
Practice making cuts with older twigs to ensure you don’t waste a valuable scion. Unite the stock and scion together with grafting tape. Keep the grafted plants warm and in a humid environment. You can cover the grafted area with a clear plastic bag to promote humidity.
Tissue Culture
It’s a micro-propagation technique where the small pieces of clean tissue from a leaf bud or flower stays in a medium or gel in a plant laboratory. The medium encourages the tissue to clone and multiply itself. The method mostly applies to the commercial production of plants needed in huge numbers. When plantlets grow, you wean them from a gel to a potting mix.
Can You Grow Rhododendron from a Branch?
Rhododendron can grow from a branch as a vegetative method in three ways. They include layering, cutting, and grafting. The twig requires a unique selection like one that is healthy, firm, and green. Incase the stems have many leaves or a terminal bud, remove them. The plant produced looks similar to the mother plant. Cutting as one of the standard methods has a greater success rate than growing some species from seeds.
Conclusion
In selecting any methods in propagating the plant, consider its pros and cons. For instance, vegetative means like layering, cutting will reproduce a replica of the mother plant. But the vegetative means may take too long to form a seedling.
The seeds bring about variations in the new plant, which are both desirable and undesirable. But the ovules are easy to grow and take care of them. The only concern it’s when the seeds are too tiny and may require special treatment.