We use the non-linear spherical model in cold dark matter ( CDM ) cosmologies with dark energy to investigate the effects of dark energy on the growth of structure and the formation of virialised structures . We consider dark energy models with a constant equation of state parameter w . For -1 < w < -1 / 3 , clusters form earlier and are more concentrated in quintessence than in \Lambda CDM models , but they form later and are less concentrated than in the corresponding open model with the same matter density and no dark energy . We point out some confusion in the literature around the expression of the collapse factor ( ratio of the radius of the sphere at virialisation to that at turn-around ) derived from the virial theorem . We use the Sheth & Tormen extension of the Press-Schechter framework to calculate the evolution of the cluster abundance in different models and show the sensitivity of the cluster abundance to both the amplitude of the mass fluctuations , \sigma _ { 8 } , and the \sigma _ { 8 } - w normalisation , selected to match either the cosmic microwave background observations or the abundance of X-ray clusters .