Growing Rhododendrons from seed is a quick and easy way to fill your garden. It is a really simple process and can easily be done at home. Perhaps the most satisfying aspect of gardening is to see your own flowering plants that have been grown on from seed sown by yourself.
Growing Rhododendron from Seed – A Simple Guide
Obtaining Seed
The first part of the process is to obtain fresh seed from one of the seed exchanges run by the rhododendron groups. Willie Campbell has been Seed Exchange Manager for the Scottish Rhododendron Society (SRS) since 2008. It involves annually creating a listing of seeds received from donors across the country and Europe.
There has been many changes in the last few years. Since 2013 the SRS have complied with the NAGOYA protocol, which in essence does not allow us to accept and distribute “Wild Collected” seed from what we called “Plant Hunting Expeditions”. For many years we had seed collected by Alan Clark, Keith Rushford and latterly in 2012 Willie Campbell made a trip to Sichuan, collecting seed for the seed exchange. All these collections of seed were annotated with collection numbers, e.g. AC (Alan Clark), KR (Keith Rushford) and CNC (Cox, Newton and Campbell).
Hand pollinated seed donations have dropped off. Once Peter Cox and Alan Anderson would contribute maybe 50 lots of seed. In recent years we have had increasing numbers of Open Pollinated seed donated, carefully sourced from species rich gardens. We always say that a few of the seedlings may not be the same as the true species. However, I have grown seed “wild collected” and sometimes in a batch of seedlings you get variation in the plants or just slight differences.
Reproducing Rhododendron Species from Seed
A guide to hand pollination by Alan Anderson
Peat Statement
We have suggested peat as a growing medium because it is a tried and tested method that will produce good results. However, we all have a responsibility to find sustainable alternatives and it is worth experimenting with other types of compost. Some suggestions are highlighted in our peat survey.
Seed Sowing Process
- Seed will germinate at any time of the year but sow early (February) to give seedlings a better chance of making it through their first winter.
- An empty plastic grape or tomato container is ideal as long as it has holes in it for drainage.
- What compost do we use ? Best is peat if you can get it, with a few granules of slow-release fertiliser. Half-fill the container with the compost and leave in tray of water to dampen the compost.
- No need to tap down the compost, you just sow the seed evenly on the surface. Do not cover the seed, but using a water sprayer, gently spray the seed to anchor seeds to compost. Make sure you label !
- Then you take some clingfilm and completely cover the plastic container, sealing in the moisture in the container.
- The container is then put in a warm room for seeds to germinate, not direct sunlight as this is a quick killer of seedling rhododendrons.
- Within 3 to 4 weeks, you should see signs of germination then you can take of the clingfilm cover (this prevents damping off) and again put somewhere warm, moist and most of all in shade. Note direct sunlight is a rhododendron seedling nightmare.
- After the plants reach the 5-leaf stage, transplant the seedlings into trays, pots or whatever is your preference. Again, shade is required. Compost again is better peat based, with some perlite added as many of the new ericaceous composts contain a high proportion of wood chip and dries out quite quickly on the surface making you water more often and then underneath becomes too soggy. Spray weekly with a week solution of soluble ericaceous fertiliser. Make sure you label.
- For the first winter keep in glasshouse or cold frame out of the coldest days.
Bringing on your seedlings
Next spring or a year since the seed was sown, you should have a decent plant and it’s now time to consider how you are going to grow on until planting out in the garden, woodlands or taking to your friends.
I used to in my Pro gardening days, line out the plants in raised beds of compost rich leaf mould I made on the estate each year, sometimes if it was too sunny, I would cover with mesh or fleece, watering when dry and so on. Make sure you label !
Most of us don’t have that space, and if you are like me have a succession of plants coming along, I pot up and label each plant and that’s the time to look at what you need for yourself or share with others or bring along to your local plant stall.
One tip I will always give at the start of each May is to pinch out the growing tips to make sure the plants do not become leggy and make a bushy plant. After 3 to 4 years you will have a plant ready to plant in the garden. I do hope that helps you grow rhododendrons from seed, it’s easy, quick and exciting.
By Willie Campbell
My First Attempts at Propagating Rhododendrons
Part 1: Seed Propagation by Paul Haynes
Hands-on experience is by far the best way to learn propagation techniques. Come along to one of our practical workshops to see expert demonstrations. Video below.
SRS Seed Propagation Workshop video
SRS propagation workshop. Filmed and edited by John Roy