The Landau decrement associated with sinusoidal electron‐plasma wave propagation undergoes decaying oscillations in time. The weakening of the oscillations between growing and damped waves is due to phase mixing of resonance particle motions. The rate of phase mixing is increased by the effects of collisions between resonance electrons and the bulk of the plasma particles. The phase mixing problem has been studied, and it is found that the amplitude of the oscillations in the Landau decrement decreases inversely with the square root of the time for early times, and inversely with the seven‐halves power for late times.