A Well
Neighbor in a jar
Dickinson's typical compression—water is both close (in the well) and impossibly distant (underground). The jar image makes it domestic and strange at once.
Grass as 'he'
She genders the grass masculine throughout. In her era, masculine pronouns often marked the rational/bold versus feminine fear—she's noting the grass's courage.
Sedge by the sea
Sedge grows in coastal marshes where water has no bottom—'floorless.' The grass family isn't afraid of abysses humans fear.
Haunted house
Those who 'cite' nature are scientists and naturalists. She's saying even experts haven't entered nature's real mystery—they catalog the outside.