"Puffballs" can be any of a number of types of fungi. Unlike plants, all
fungi need is enough dead plant material to eat, and enough water to
produce the reproductive sporific phase of the life cycle (the puffball).
The puffball is only a small portion of the overall fungus body, the
majority of the organism lives in the soil underneath the concrete
decomposing plant material. Since they have no vascular tissue at all,
all they need is enough moisture underneath the concrete, and enough
contiguous tissue joining the puffball to the rest of the fungi.