Re: What elements are necessary for grafting?

Successful grafting requires first that the stock and scion be compatible. The 
more distantly related they are the lower the chance of grafting success. The 
stock and scion must be in the proper stage of growth. The scions must must not 
be allowed to dry out before grafting. The stock and scion must be cut to fit 
together tightly, and their cambia must be lined up with each other. Poor 
technique of cutting and fitting stock and scion together is a common cause of 
failure for inexperienced grafters.

Correct polarity must be maintained, that is the base of the scion is grafted 
to the top of the stock. The graft union must not be allowed to dry out so a 
grafting wax may be used although in some species a wax is not used to allow 
adequate oxygen to reach the graft union. Oxygen requirements seem to vary 
depending on species. The graft union must be given optimal temperature and 
humidity conditions to allow cell growth.

Some species are just more difficult to graft than others so the percentage of 
successful grafts may be lower. Difficult-to-graft species include oak, beech 
and hickory. Virus, insect or disease infected stocks or scions can reduce 
grafting success.

Reference

Hartmann, H.T. and Kester, D.E. 1983. Plant Propagation: Principles and 
Practices. Englewood Cliffs, NJ: Prentice-Hall.