Success with Rhododendrons and Azaleas

by H. Edward Reiley

Reviewed by M.J. Harvey  March 2005


I deduce that this book started out as a modest ‘How-to Book’, in this case ‘How to Grow Rhododendrons’, covering their cultivation, propagation, physiology, pests and diseases, and in this respect it succeeds very effectively.  Then it grew, like Topsy, but let me comment on the basics first.


Chapter 2, ‘Site Selection and Growing Requirements’, is a very thorough discussion of soil and site characteristics (pH, minerals, drainage, organic matter, soil bacteria and fungi, light, wind, air drainage and temperature).  In some ways this is the most satisfactory part of the book and is required reading for all growers.  I was fascinated by the account of the 1996 discovery of ‘glomalin’ by Dr. Sara F. Wright.  Glomalin is the soil ‘superglue’ found in the soil organic matter and produced by mycorrhizae.  It binds silt, sand and clay particles together adding structure and tilth to the soil.  Soils have been studied for centuries and the separation of a newly discovered fraction is a surprise.


Chapter 3, ‘Selection of Rhododendrons’, has sensible words on site selection and how exposure and plant competitors govern how well a plant performs.  Most of the chapter is taken up with ‘Good Doer’ lists contributed by growers in their particular region.  The USA is very thoroughly covered (the author resides in Maryland), but Australia, Canada (Ontario and BC) and the British Isles are mentioned, although the last time I was there Scotland was not to the ‘southeast of Manchester’ – I think two lists are switched.  A map shows the plant hardiness zones, unfortunately in black and white, but the new (1997) American Horticulture Society Heat Zone Map is in full colour.  The latter maps the average number of days per year over 30o C and while it is similar to the older hardiness zone map (average minimum temperature) there are subtle differences, mainly in the continental interior.  It is welcome to have the heat map since some plants are knocked out by summer heat rather than winter cold.  One slight irritant to a non-US citizen is that the USA is shown as an island surrounded by sea and while this may at times reflect some political attitudes, a few dotted lines indicating the existence of Mexico and Canada would be a courtesy for gardeners in other countries.  There is even a hardiness map of Canada available.


Chapter 5 covers ‘Rhododendrons in the Landscape’ – the arrangement of plants, the use of trees and companion plants, and even a note on bonsai.  The book progresses to transplanting followed by watering, mulching and nutrition considering the major elements:  nitrogen, phosphorus and potassium, as well as the minor elements.  The author recommends the use of the rapid-acting ammonium sulphate as well as the slow-release urea-formaldehyde for providing nitrogen in the correct form (ammonium) for Ericaceae.


‘Plant Disorders’ covers fungi, insects and physiological problems with the injunction that if the plant cultivar is not suitable for the region nothing will save it.  The traditional fungi are mentioned but the recent introduction of Sudden Oak Death (Phytophthora ramorum) did not get included.


The chapter on propagation is excellent, covering cuttings (including the need to use early softwood material for deciduous azaleas), various grafting techniques and seed germination.  These problems are extended to the additional troubles that running a nursery entails.  The book concludes with hybridizing, running flower shows and ends with an alphabetical list of good performers with their hardiness, 10-year height, flower colour, flowering season and comments.  An additional appendix lists heat-tolerant species and hybrids.


So far this is a wonderful book but I have a few reservations.  Chapter 1 is an introduction to what rhododendrons are, their world distribution and early explorers (with poor old Augustine Henry spelt ‘Henny’).  It really isn’t necessary to include these in a book on cultivation.  These subjects are now covered in other books unlike when David Leach published his then wonderful ‘Rhododendrons of the World’ in 1961.  I think Dr. Reiley has too slavishly copied the Leach formula – this certainly applies to the Leach maps of Rhododendron regions of the world that are copied at too small a scale to be comprehensible.


The severest criticism is the section of colour photographs that have been added for this edition.  Flower and garden photography is now a developed art but the examples here show numerous errors of lighting, colour balance, posing and framing.  No longer can you go out with a camera and ‘click’ on a bunch of plants.  A professional should have been hired.


Then there is a section on ‘Native azaleas’ (meaning, of the USA), contributed by Donald W. Hyatt.  This is completely irrelevant to a book on cultivation – and completely wonderful.  I am grateful that it got thrown in and was particularly interested to hear of a recently (1999) described species, R. eastmannii, restricted in the wild to two counties of South Carolina.  It is deciduous with delightfully fragrant white flowers with a yellow blotch appearing after the foliage has expanded.


Although a more severe editing and proofreading were needed (for example ‘Purple Splendour’ is a registered name and cannot have the final ‘u’ omitted), I am enthusiastic about this book; it covers a range of topics not collected together elsewhere and all rhodoholics should have a copy.  Published by Timber Press in paperback, $34.95Can.