In the first stanza the poet says once he planted a seed in some good time that over the years blossomed into a beautiful flower; but people criticized it and called it a weed. All those who passed by his garden saw the flower and expressing their disapproval of its beauty would keep on criticizing
Meaning by that they are the lords/guardians sons or daughters of the time being.
It is Subjunctive. Conditionals use "If"
I sat on the chair . The girl sat on the couch to read a book.
