According to the present application, a harvesting method is proposed for harvesting asparagus that does not suffer from the practical problems of the prior art disclosure. This method is characterised by placing an RF antenna in grid locations on an earth dam being cultivated to contain a sand bed with a moisture gradient that is held constant by, in a free space above the earth dam, transmitting a signal through the antenna in a plurality of selected frequencies in a range of 1 - 10 GHz constructing an image from received signals in the grid locations for the plurality of selected frequencies and detecting in designated grid locations, from absence of image signal in multiple of said selected frequencies, presence and height information of an asparagus spear having a moisture component.
