In just three short lines, a gardener's whole day slips by. Morning and noon turn into "green evening," as if the hours themselves have been absorbed into the plants. The speaker doesn't tell us about the passing time directly. Instead, the day is measured in green, in growing things, which suggests a person so wrapped up in the garden that the sun's movement barely registers.
The last line is the most interesting. The speaker waters "my bed," which could simply mean a flower bed, but the word also makes us think of a place to sleep. The garden and the speaker's own rest seem to blur together, as if tending the plants is a way of settling down for the night. The mood is quiet, patient, and content. Nothing dramatic happens, and that is the point: there is a gentle satisfaction in ordinary work, and a sense that time spent this way is never wasted.