Pukekura Park - its ecology and history - Friends of Pukekura Park New Plymouth Inc.


Techniques for Propagating the Older Rhododendrons (and Camellias)

Ken Davey

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In today’s world many of the Rhodo’s that you can buy are available because they are easy to propagate from cuttings, grow to a saleable size quickly and flower well as young plants. You will also notice that many of them have small to medium sized leaves.

 

Many of the older cultivars have larger leaves and corresponding flower head sizes.


In the days before the advent of mist propagation most Rhodo’s were propagated by layering, grafting or using hardwood cuttings put in to overwinter in a closed cold frame.


Layering took up a lot of field space in a nursery and was not always successful.

This method is still used today for a few cultivars that do not respond well to other methods of propagation.


Grafting was used for many cultivars that were too upright in growth for layering, or were naturally very slow growing. Many of the rootstocks used were seedlings and the result was a great variation in growth rate of the grafted cultivar due to the variability of the seedling rootstock’s own growth rate.

 

There were also problems of matching the scion diameter to the diameter of the seedling’s stem, as many of the cultivars had very large stem diameters, the worst being the giant leaved species and hybrids in the Rh Grande and Sinogrande series.

 

Another problem with grafting was and still is to be able to graft low enough on the stock to reduce the problem of rootstock suckering.

 

Today grafting is still done on a limited scale and instead of using seedlings as rootstocks, cuttings of an easy to root cultivar are used. The grafts are often done using unrooted cuttings of the rootstock. The completed graft is then placed under mist or in a high humidity propagation tent with bottom heat to encourage callusing (uniting) of the graft and the formation of roots on the rootstock cutting.


As the physiology of rooting cuttings became more widely understood and mist propagation and other aids became more commonly used, cutting propagation became the norm, along with that came the trend towards using only those cultivars that rooted easily and produced a saleable plant in a short time.

 

These days with the average garden getting smaller, the larger growing and also larger leafed cultivars are losing out to the smaller growing ones. It won’t be long before the only places that these larger and bolder plants will be seen will be large private gardens and public parks.

 

It may be that with the demise of local body nurseries and the training they provided that the only way to repropagate these older cultivars is to get one or two commercial nurseries to grow them.

 

For many Rhodo species and cultivars there are definite cutting collection times.

 

As far as I know all the soils in Taranaki are suitable for growing just about all Rhododendrons.


Replacement Camellias are much easier to propagate. The bulk of them will grow with relative ease from cuttings. By hunting around, many of the older cultivars can be found in nursery lists from around the country.

Any difficult species or cultivars can be easily grafted on seedling stock or on rooted cuttings of easy to propagate cultivars.

 

In all cases cuttings have an optimum time for collection and propagation, but with Camellias, fair results can be obtained by taking cuttings at just about any time of year.


If the required plants are not in the trade, then any plant replacement from existing stock will take several years of nursery growing before flowering can or is likely to occur.

 

Reproduced from The Newsletter of the Friends of Pukekura Park 1(1) (November 2006)

 

Abstract:
Various methods and problems of propagating replacement plants from older cultivars of Rhododendron and Camellia are discussed and explained.  Choice of method and technique has widened since the advent of mist propagation and high humidity propagation tents.  Trends towards propagating for quick results and smaller gardens have influenced the commercial sector. Fewer of the older varieties with larger leaves and bigger flower heads are now offered.  Practical advice in the use of cuttings from rootstock, and other options for achieving specific propagation outcomes are given.

Keywords:
Layering, cuttings, mist propagation, hardwood cuttings, rootstock, grafting, replacing older cultivars, large rhododendrons, camellias, plant nursery practices, propagating trends. 

 


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