Leaves of flowering plants may curl due to heat stress, even when there is ample soil moisture. During periods of extreme heat, leaves curl and plants wilt when roots are unable to supply sufficient moisture to the stems and leaves. This occurs because moisture is evaporating from the leaves faster than the roots can supply it. Wilting for short periods of time does not harm plants. If there is ample soil moisture, the plant will absorb water in the evening to firm up the stems and leaves.