I gave Harry a wand made of holly wood back in 1990, when I first drafted chapter six of ‘Philosopher’s Stone’. It was not an arbitrary decision: holly has certain connotations that were perfect for Harry, particularly when contrasted with the traditional associations of yew, from which Voldemort’s wand is made. European tradition has it that the holly tree (the name comes from ‘holy’) repels evil, while yew, which can achieve astonishing longevity (there are British yew trees over two thousand years old), can symbolise both death and resurrection; the sap is also poisonous.
Some time after I had given Harry his holly-and-phoenix wand I came across a description of how the Celts had assigned trees to different parts of the year and discovered that, entirely by coincidence, I had assigned Harry the ‘correct’ wood for his day of birth. I therefore decided to give Ron and Hermione Celtic wand woods, too. Ron, who was born in the February 18 - March 17 period, was given an ash wand (I think I had originally marked him down for beech), and Hermione, who was born between September 2 and September 29, received a vine wood wand (I can’t remember what I originally stipulated for Hermione; possibly I had not specified a wood for her at that stage).
I have only used the Celtic assignations for Ron and Hermione. Hagrid, for instance, has an oak wand though by this Celtic system he should have a wand made of elder; in Britain, the oak is ‘King of the Forest’ and symbolises strength, protection and fecundity; what other wood could ‘choose’ Hagrid? In any case, I liked having a hidden connection between Harry, Ron and Hermione’s wands that only I knew about (until now, anyway).
For those who are interested in the trees assigned to the different parts of the Celtic year, below is the chart that I used. I apologise to any Celtic tree experts out there for any inaccuracies I may have reproduced (I have found slight variations between sources since I first came across this information.)
December 24 - January 20 = Birch (Beth)
January 21 - February 17 = Rowan (Luis)
February 18 - March 17 = Ash (Nion)
March 18 - April 14 = Alder (Fearn)
April 15 - May 12 = Willow (Saille)
May 13 - June 9 = Hawthorn (Huath)
June 10 - July 7 = Oak (Duir)
July 8 - August 4 = Holly (Tinne)
August 5 - September 1 = Hazel (Coll)
September 2 - September 29 = Vine (Muin)
September 30 - October 27 = Ivy (Gort)
October 28 - November 24 = Reed (Ngetal)
November 25 - December 23 = Elder (Ruis)