Minhbach's Weblog

May 27, 2012


Filed under: Flowers, Garden — Tags: — minhbach @ 4:45 am

A simple and reliable method of propagating rhododendrons

A simple and reliable method of propagating rhododendrons is via semi-ripe cuttings and mid- to late-August is a good time to do this.

Choose healthy shoots on the current season’s growth and take cuttings approximately 8cm to 10cm (3in to 4in) long, making the cut with a sharp, clean knife just below a leaf node. Remove any side shoots along the length of the cutting and all the leaves in the lower third. After wounding the bottom 4cm (1.5in) of the cutting, insert into a general cuttings compost. Ensure that the cuttings are spaced so that their leaves don’t touch. Place in a propagating unit or insulated cold frame and shade from direct sun.

Check your cuttings daily and remove any fallen leaves as they may otherwise harbour pests and diseases. Once your cuttings have rooted you can help them along with a fortnightly feed of balanced liquid fertiliser.

When to take cuttings:
Most evergreen rhododendron and azaleas may be propagated from stem cuttings. Cuttings are usually taken from mid July to early fall (September) from new growth that is just hardening off (known as semi hardwood). Cuttings are taken in the morning when full of moisture.

What kind of cutting:
The wood should be firm and just beginning to brown at the base. To see if your shoot is ready, bend it between your fingers. If it breaks, the shoot is either too soft or too hard. If it’s pliable and springs back when you let go, the shoot is at the right stage. The leaves should be mature.

Size of cutting:
Cuttings should be 3-6 inches long. The cuttings are usually terminal cuttings with one whirl of leaves at the top. Take off the bottom half of the leaves (to reduce the leaf area) and any flower buds. The cutting has the end cut off just before placing in rooting hormone powder (containing a fungicide if you wish). Be sure to shake off excess rooting hormone powder.

Soil mixture:
Then the cuttings are placed in a flat of sterile media containing a mix of 50% peat moss, and 50% horticultural perlite or vermiculite. Peat and perlite are probably the best but is expensive. Do not use any fertilizer! You want the roots to have to search for food and in doing so the root mass is larger. Also, new root tissue can be damaged by fertilizer salts. The propagation flat should be 4 or more inches deep preferably. The flat (one that is able to drain) which is now full of cuttings is placed in a clear polyethylene bag with struts (you can use sticks in each corner or a wire hoop) to keep the clear bag away from the foliage and placed in a light area with no direct sunlight. The plastic should not be airtight so the plants can breathe. Cuttings need a protected high humidity environment while they root. Cuttings don’t have roots to take up water but they still lose moisture through their leaves. By keeping the air moist, you minimize the water loss and help the cuttings survive until they can support themselves. You can place them in a shaded greenhouse or frame… or on a window-sill indoors. Grow light bulbs can be used to supplement inadequate lighting. But remember… no direct outside sunlight.

Water with ordinary tap water that is at room temp when needed. Do not let the soil dry out. The flat is rotated once or twice a week to compensate variations in light and temperature. Usually bottom warmth of 75°F is used to encourage root growth. Rooting usually takes about 6 weeks for evergreen azaleas and 3 to 4 months for large-leaf rhododendron. Once the cuttings have rooted, pot or transplant them to flats containing a sterile mix of 60% peat moss and 40% perlite. Fertilize once a month with an acid-based azalea plant food like Peters. Removing terminal buds promotes sturdy well branched plant


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