A cover for a plant-growing medium comprises a main cover portion, a peripheral base spaced from the main cover portion and defining an outer perimeter of the cover, and a peripheral wall extending from a first side of the main cover portion between the main cover portion and the peripheral base. One or more plant growth channels are defined by one or more tubes extending from the first side of the main cover portion. Each tube has a proximal end adjacent the main cover portion and a distal end relative to the proximal end, with a first aperture defined in the main cover portion at the proximal end of the tube and a second aperture defined at the distal end of the tube. The first aperture and the second aperture communicate through the tube to define each plant growth channel.