I have found that if your plots are close together and a "like" is placed on one edge, it will affect all plants in that group. In my garden, i have medium 6 plots side by side, and a "like" placed at the end of that line affects all 6 plots. So technically, a "like" can affect 6 medium plots in all directions.
I have 24 medium enchanted soils plotted that fit with-in the large spell ring, a small gap, then another identical 24 plot grouping beside that. The "like" placed in the gap between the two large spell ring "footprints" affects all 48 plants within the two groups.