Rhododendron Propagation from Cuttings, A Review
by Warren Berg, Kent Washington
There are so many variables and different ideas on rooting rhododendrons from cuttings. that it is impossible to cover all the possibilities. This article is presented as a summation of ideas and suggestions on a method which has proven very successful for me-hopefully, you'll get one new idea.
- Select cuttings from healthy vigorous plants.
- Use only a low nitrogen fertilizer. Fertilize sparingly.
- Cuttings may be taken anytime from July to October after the current year's growth becomes mature. Use mist propagation if material is taken early.
- Take cuttings with terminal leaf buds. If this is not possible, remove the flower bud.
- Use intermediate-sized wood, avoiding large fast growing top growth or wood that has become lignified (turned brown). Material from young stock plants seems to root more readily.
- Cuttings should be taken in the morning from well watered plants. Collect in slightly moistened plastic bags and place in the bench as soon as possible. Store in refrigerator if there is to be a delay.
- To prepare cuttings, remove all but the top rosette of leaves (3 minimum). If necessary, leaves may be shortened by ½ their length.
- Cutting length should be 2½" to 3" on standard varieties.
- Wound cuttings with a 1 to 1½" slice on two sides. Use a deep wound, cutting through the cambium layer to include part of the inner wood.
- Use a very sharp knife or razor blade.
- Apply rooting hormone immediately after wounding, using one of the following: either (a) Hormodin (IBA) #3; or (b) Rootone (ANA) #10 plus 50% Captan wettable powder (one part to ten); or (c) Jiffy Grow #2. A mixture of ½ IBA and ½ ANA plus 10% Captan is very good. If Jiffy Grow is used, dilute at a 1:10 ratio.
- Insert cuttings in rooting medium without overlapping; water sparingly to settle. Do not tamp them in.
Rooting Medium, Temperature and Humidity
- Use a rooting medium of equal parts peat moss (best grade available), and horticulture grade perlite (medium size).
- Maintain temperature of 72 to 75 degrees F.
- Dwarf alpine types taken in September and October may be rooted in a very sharp sand without bottom heat.
- Either intermittent mist or a polyethylene plastic tent may be used. Balance screen control is suggested for mist system. However, if a timer is used, set interval at 10 to 15 seconds on each 5 to 10 minutes. Turn off at night if practicable.
- With plastic tent system, use 2 mil polyethylene with at least 12" air space above the medium.
- DO NOT place where it may be exposed to direct sunlight at any time.
- DO NOT water after initial application.
- Do not use foliar spray during root initiation.
- Transplant rooted cuttings into a bench or flat of coarse peat. Water in with Captan and ½ strength Rapid Grow (or equivalent).
- Maintain high humidity with temperature above 50 degrees F. for 2 or 3 weeks.
- Do not use bottom heat during winter, unless supplemental lighting is also used.
- Plants may be planted out in the Spring after the last frost or after the first flush of new growth has hardened off.
- Terminal buds should be removed when they first begin to swell in order to provide a well branched plant.
- Plant growth may be started earlier than normal in early spring by use of 24 hour artificial light for 6 weeks and increasing bottom temperature to above 50 degrees (70 degrees suggested). Also begin application of liquid fertilizer at 3 week intervals.
- Keep equipment and workbenches clean. All flats or wood benches should be treated with copper naphthenate. (2% in mineral spirits solvent).
- Use fungicide dip where appropriate. Pots or containers should be sterilized before reuse
- If soil is used for transplanting from the cutting bench, it should be chemically treated first.