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The best way to propagate rhododendrons is to take cuttings. It’s easy to take the cuttings, but it’s a long and fairly difficult process to grow them successfully. But that’s OK, just take lots of cuttings. Here’s how to do this.
When to take rhododendron cuttings
I have found that the best time to take rhododendron cuttings is during the warmer summer months. Aim for between the end of July and the middle of August in the UK. Taking them later than this will still work, but this is the optimum time, and I find they have always rooted more successfully and quicker.
What cuttings to take
You need to be selective in what you cut from your rhododendron plant. You want to take the healthiest cuttings that have the best chance of survival.
Look for old wood that’s at least two years old. Then look at all the new shoots coming of it; this is what you cut. Don’t take anything that’s longer than 15cm as it will have a hard time establishing a root system. Also, don’t take anything that bends easily between your fingers as that’s too floppy as I have found they are more likely to rot. On the other hand, reject anything too rigid as it’s probably too old and too hard to propagate. You need cuttings that are just right. Take selection and taking cutting is probably the difference between a good success rate and a poor success rate.
Preparing the propagation pots or trays
You need to have everything ready to go before you take the cuttings. Set up the pots or trays with sterile potting mix; seed and cutting compost is fine. Pack it fairly loosely into the trays or pots as it has to drain easily.
Taking rhododendron cuttings
Sterilise your cutting tool well to avoid spreading disease between the plants. Cut cleanly at the base of the stem that you want. Don’t saw back and forth and leave a jagged edge – this stresses the plant out. If your cutting has large leaves, cut the leaves in half. You don’t want the cutting to waste energy on maintaining large leaves instead of using it to create a root system.
Take all the cuttings you want and then move directly on to the next step, planting them.
Planting rhododendron cuttings
Dip the end of each cutting into hormone rooting powder to give them a good start. Place the cuttings in the pots or trays, with one-third of the cutting below the level of the soil.
Caring for the cuttings
Rhododendrons can take between six to eight months to propagate to the point they can be transplanted. During this time (which includes over the winter), keep them at around 18˚C. Expose them to some sunlight and keep them well watered. Remember that these plants need to be well drained and not become water-logged.
If any of the cuttings look unwell or turn brown, remove them immediately. They may have succumbed to an infection or fungal rot that can spread quickly.
Transplanting the cuttings
As I said above, the cuttings should have established a strong root system in six to eight months. Check the roots and if they’re strong enough, transplant the cuttings to larger pots. You now have to keep them in a greenhouse or cold frame for another year before they’re ready to enter your garden. It takes a long time to propagate rhododendrons.
Planting out the rhododendrons
By April of the second year following taking the cuttings, your rhododendrons should be ready to plant out in your garden or in pots (See the Planting rhododendrons in pots article.) Remember to acclimatise the plants slowly to their new habitat, so they don’t become stressed.
If you have issues with your rhododendrons, don’t forget to check my guide on rhododendron pests and diseases as well as how to prune them here. Mildew can also be an issue, as well as drooping leaves.