Ultrafast ultrasound imaging offers great opportunities to new imaging technologies such as shear wave elastography and ultrafast Doppler. Multiplane wave (MW) imaging is a new technique in which multiple positively or negatively encoded plane waves are emitted successively with short interleaved time during one transmission event (i.e. pulse-echo event), aiming at increasing the signal-to-noise ratio (SNR) of ultrafast imaging. However, the long transmit pulses of MW imaging also increase the reverberation artifacts. Here we propose a delay-encoded harmonic imaging (DE-HI) technique to enable HI for MW imaging to reduce reverberation. DE-HI encodes the 2nd harmonic signals with transmit delays rather than reversing the pulse polarities, thus addressing the MW encoding challenge that the 2nd harmonic polarity is independent of transmit pulse. DE-HI improves the ultrafast imaging by reducing the reverberation with HI and increasing SNR by emitting multiplane waves.