Why does jasmine bloom only in the night?

Nastic movement is responsible for blossoming of flowers. Usually this movement takes place in a flat plant part oriented relative to the plant body and produced by diffuse stimuli causing disproportionate growth or increased turgor pressue in the tissues of one surface. It normally occurs in leaves and petals which are bilaterally symmetrical.

          Changes in the environment send a signal to the plant and result in a differential growth between the upper and lower surfaces of petals resulting in blossoming of flowers and different conditions.

            In case of jasmine, this response occurs due to stimulus caused by the change over from brightness to darkness.

            As there is more growth on the upper sides (epinastic movement) of the petals, the flower opens. If there is more growth on the lower side of petals the flower closes (hyponastic movement).