I am not an expert by any means, but I do dabble.

I have about half a dozen on the go, I have Oaks that appear on my allotment as a result of the squirrels burying acorns and forgetting them.

I also have a Sycamore that must have helicoptered into my allotment and grew.

I also have a couple of Acer davidii.

I tend to follow the basic information here;

http://www.thegardenersalmanac.co.uk/Data/Bonsai/Bonsai.htm

But as I suggest in the article, if I want the real low down on the subject, I visit a dedicated bonsai site.

I use this website:

http://www.makebonsai.com/guide/bonsailink.asp?quicklink=5049

It says re-pot every 3-4 years.

when there very young you repot back into the same pot every year and add proper bonzei soil . you do this while there dorement either very late summer or my personel choice very early spring . as they get older you can repot them less often . the bigger the pot the bigger the tree .

thanks very much for the info. Very informative.

your welcome .id get a book on the subject as theres a lot more to it ie wiring the branches to shape , getting roots bare or pulling all the leaves of so the next leaves grow smaller . also leaving and causing partial die back . anything to give a small tree the look of age .also bleeching said dead branches etc .