Sediment suspension is a common and important phenomenon in planetary atmospheres. A widely-used suspension criterion, also a proxy boundary layer wind-speed indicator, was discredited by Mars Exploration Rover Mission results concerning sediment particle sizes in active surface bed forms. Parameterisation of a new dynamic suspension criterion based upon turbulent stress yields predicted suspension threshold conditions consistent with those inferred for Earth and predicts no suspension of sand-grade particles for recent Martian wind velocities (at 1m height) estimated in the range 28--73 m s-1. Results for Venus imply suspension of very fine sand particles at low surface wind speeds.