ZnO nanostructures of different morphologies were grown in a controlled manner by a novel sonication assisted sol gel process. Variation in the alcoholic medium resulted in nanorods and flower like ZnO nanostructures. Flower like ZnO nanostructures with a root size of 1m and a tip of 150nm were synthesized using ethanol as solvent, while ZnO nanorods with diameter less than 60 nm and length greater than 1m were synthesized using methanol as solvent. The samples were characterized by X-ray diffraction and Scanning Electron Microscopy. The XRD results show the formation of highly crystalline ZnO with no detectable level of impurity. In this paper, a possible mechanism for the variation of morphology with the change in solvent has been discussed. The effect of solvent vapour pressure on the sonication process has been explained. The solvent vapour pressure has an effect on the intensity of sonication which affects various chemical reactions taking place during the formation of ZnO. The effect of ethylenediamine on the chemical reactions leading to formation of ZnO nanostructures has also been analyzed.