I saw a crowd, A host of golden daffodils; Beside the lake, beneath the trees, Fluttering and dancing in the breeze. Continuous as the stars that shine and twinkle on the Milky Way, They stretched in never-ending line along the margin of a bay: Ten thousand saw I at a glance, tossing their heads in sprightly dance
Which is from "Ode to Autumn" of course and that's what "thou" and "thy" refer to - Autumn - not spring.