The iPad camera sharpens the eye, no question; I never spotted the physics of milk jugs before. Since the milk jugs are little greenhouses, they capture the warmth of the sun; they have thermal mass, and melt themselves into the snow pack. The image shows the squash patch, which (at least at this time of the year) captures the most sunlight. How do we know that? Because of all the sets of milk jugs set out in the garden, this one is most deeply sunk in snow.

The milk jugs extend the season; but they also instrument the garden. I wonder if there are other ultra-low-tech, functionally stacked solutions like this?