Mount Arrowsmith Rhododendron Society: Propagation Group
As part of our mandate to raise public awareness of the genus ‘rhododendron’, we have an active Propagation Group. An informal sub-group of our main membership, the Propagation Group takes cuttings from a wide range of hybrid and species rhododendrons, from heirloom varieties no longer available in stores, to garden standbys, to rare and unusual types.
Group members get together in planting bees, where raw cuttings are prepared by stripping away lower leaves, wounding the stem, and dipping in hormone powder. The prepared cuttings are then stuck in propagation medium and rooted under controlled temperature, light, and humidity conditions.
For the first three weeks, the light, warmth, and humidity ‘wake up’ the cuttings so that they start to grow callus tissue at the cambium layer of the cut stem. After about 6 weeks, roots start growing from this callus. Then leaves develop, creating a whole new plant.
Due to a variety of factors, approximately 50% of the cuttings don’t “take”. Our group is
relatively new at this, so we’re experimenting to see if we can increase our success rate; but even professional propagators don’t achieve 100% success.
From the cuttings that survive, the tiny plants are grown on and repotted as they get bigger, to be sold to the public or given away in raffle draws at our meetings.
Here’s a video from April 2020 of our latest crop of cuttings (struck November 2019, see article below), which are currently being cared for by staff from the Vancouver Island University since we don’t have access to the greenhouse during the COVID-19 situation.
(Click on the image to go to the video, then click the Play button to view)
- Cuttings are trimmed back to a few inches long with a clean diagonal cut.
- All but the top three or four leaves are removed.
- The side of the stem is wounded with a shallow cut.
- For varieties with larger leaves, the leaves of the cuttings are trimmed back to half their size to control moisture loss.
- The raw parts of the stem are dipped in rooting hormone, then stuck into the moist propagation medium, which is a sterile mix of 1:1 peat moss and perlite.
- Ideal rooting conditions are cool and humid with bottom heat.
- Smaller-leaved rhodos as well as augustinii and williamsianum hybrids are easier to root than some others.
- Cuttings should be as fresh as possible when stuck, but can be taken a few days earlier if kept cool and moist in a plastic bag.
- Stems that are smaller than a pencil work best.
- Stems with a leaf bud are usually easier to root than those with a fat flower bud.
- When cutting the stem off the plant, the cut is made where it is green, just inside last year’s brown stem.
Some easier-rooting varieties:
|R. augustinii||R. williamsianum|
|‘Blaney’s Blue’||‘April Glow’|
|‘Blue Tit’||‘Bow Bells’.|
|‘Blue Peter’||‘Clayoquot Warrior’|
|‘Ilam Violet’||‘Gartendirektor Reiger’|
MARS Propagation Team Strikes 594 Cuttings
Story: Katherine Wasiak
Photos: Ron Sutton and Linda Derkach
With sharp tools, numerous tiny pots, and piles of fresh rhododendron cuttings, 13 MARS members spent the morning of November 18, 2019 at VIU’s G.R. Paine Horticultural Training Centre greenhouses, preparing and striking almost 600 cuttings.
Although old hat for some, this was a fascinating learning experience for others. We discovered (the hard way) that it is smart to pour water into the perlite bag before scooping it out to dampen down the unhealthy dust. We learned the recipe for a good propagating medium – 5 parts perlite (large and small) to 2.5 parts fine coconut coir. We saw that the best cuttings are taken from semi-ripe and not woody stems, and we were shown the correct way to trim cuttings (don’t squish stems and wound on one side of stem by cutting into the
outer layer, not the deeper cambium layer, which carries nutrients).
With assembly-line precision, cuttings were taken, wounded, moistened and dipped in rooting hormone before being carefully placed in pots. We also realized the importance of keeping careful records, labelling cuttings and creating a master list of plant numbers and varieties.
MARSians came together after a good morning’s work striking over 600 cuttings! What fun it was working together, laughing, sharing information, learning new skills and accomplishing a lot in a short period of time. Now the hard part – waiting patiently to see results of our efforts. Fingers crossed!