The genus rhododendron is an extremely large and varied group of plants that have differing abilities to root from cuttings. The large-flowering hardy hybrids and the small-leafed dwarf rhododendrons are the most worth while to propagate from stem cuttings.
Prepare the compost before taking any cuttings to avoid unnecessary delay, and water loss, before planting. Mix together equal parts lime-free grit and sifted peat. Fill a container with the compost and firm to within f in of the rim.
Take cuttings from the second flush of growth at the end of the summer, usually in September. The second flush of growth can be recognized by the umbrella of shoots that does not occur on the first flush of growth.
Remove all the leaves except the terminal whorl (the group of leaves nearest the tip). Snap out the terminal bud regardless of whether it is a flower or vegetative bud.
Place the cutting in the palm of a hand so that the top is just about level with the forefinger and the stem is across the palm of the hand. Cut the stem at the butt of the hand with a sharp pair of secateurs. This will give a cutting of about 4 in long. Cut part of the remaining leaves to reduce their leaf area and so make planting easier.
Wound the bottom f in of the cutting by making a shallow score with a sharp knife. Dip the cut surfaces in a strong rooting hormone (0.8 per cent IBA). This is particularly important for varieties with 'Britannia' in their pedigree, as they are generally difficult to root.
Make a hole with a dibber in the prepared compost and insert the cutting. Plant any further cuttings as close together as possible.
Label the container and place it in a well-lit environment with bottom heat of 21°C/70°F. Control water loss by covering the container with a very thin, clear polythene sheet or by leaving the container in a mist unit.
Prevent rots by applying a dilute fungicidal solution at regular weekly intervals.
Rooting should not be expected until well into the new year.
Harden off the rooted cuttings and transplant in late winter/early spring and label. Place them in a cold frame to grow on.
1 Fill a container with equal parts lime-free grit and sifted peat. Cut a stem of the second flush of growth in late summer.
2 Remove all the leaves except the terminal whorl. Snap out the terminal bud, irrespective of it being a flower or vegetative bud.
3 Reduce the cutting to
4 in, using a sharp pair of secateurs. Cut off part of the remaining leaves to make planting easier.
These are the easiest group from which to take cuttings, although some varieties, depending on their parentage, are more difficult than others to root successfully.
Mix thoroughly equal parts lime-free grit and sifted peat. Fill a container of suitable size with compost—allow about 1} sq. in per cutting—and firm gently.
Select a stem of the current year's growth that has set its terminal bud, which is usually in late August to September. Cut back the stem with a sharp pair of secateurs to about in from the tip. Pick or cut off any leaves on the bottom half of the cutting.
Wound the cutting by making a very shallow slice on the bottom ^in of the cutting. This wounding is not always necessary, but many varieties do benefit, and it is advisable to adopt a standard procedure. Treat the cut surfaces with rooting hormone powder, using the hardwood strength of 0.8 per cent IBA.
Make a \ in hole with a dibber in the prepared compost. Plant the cutting and water with a fungicide. Label; then place in a well-lit humid environment with bottom heat; a mist unit is ideal to produce these conditions. Once the cutting has rooted, harden off gradually in spring. Pot up and label.
4 Make a shallow score in the bottom f in of the cutting. Dip the cut surfaces in a rooting hormone.
5 Dibble the cutting into the compost. Label the container and place it in a mist unit with bottom heat of 21°C/70°F.
6 Spray each week with a fungicide. Harden off the rooted cutting and repot in early spring. Label and place in a cold frame.
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