Bent's are a kind of grass that were used for floor covering and bedding.


Robert Herrick (16th Century) in 'Ceremonies for Candlemas Eve' says ...
"Green rushes then and sweetest bents
With cooler oaken boughs
Come in for comely ornaments
To re-adorn the house"


Indeed, laying them on top of cut branches of broom would make a superior kind of bed, so the meaning could well be sexual.