A variable rate suspension system for a boom sprayer including a lift assembly and chassis. The suspension system includes a needle valve fluidly connected to a hydraulic accumulator and a first and second lift arm cylinder. A control block provides hydraulic fluid to the system and lift arm cylinders. Dampening of vertical accelerations encountered by the chassis and transmitted to the boom sprayer through the lift assembly is controlled by adjusting the rate hydraulic fluid flows from the cylinders into the accumulator using the needle valve.