A vertical quarter wave whip with ground plane applies a common trick in practical electromagnetics. The ground plane generates the mirror image of the whip and that mirror image behaves like it was feeded by inverted signal. The result is like a vertical half wave dipole in free space.
Theoretically the ground should be a large planar surface but even a bunch of separate rods which are connected to the shield of the feeding coax cable do the work acceptably.
If the ground plane is horizontal and the whip is vertical the resulted antenna directs the signal horizontally 360 degrees around the whip axis. The wave in the far field is vertically polarized (=vertical electric field). The communication would be weak with a station which has a horizontal half wave dipole.
The ground mirroring is true also with a half wave dipole. It's utilized in long distance short wave radio communication as a method to direct the beam a little upwards to get effective ionosphere reflections. The elevation of a horizontal dipole is adjusted for wanted landing zone for the ionosphere reflection. The activity of the sun varies, so reading carefully radio weather forecasts is essential for optimal shortwave communication.
MW radio stations around 1MHz often have vertical whips. The ground plane is the real ground.