The precise season in which Wordsworth revisits this favourite beauty haunt of his is not mentioned specifically, but if you read the poem carefully, there are a few clues that we can pick out that strongly suggest that the season in which this poem was written was summer, though we cannot be entirely sure. Consider the following quote:
...These plots of cottage-ground, these orchard-tufts,
Which at this season, with their unripe fruits,
Are clad in one green hue, and lose themselves
'Mid groves and copses.
Normally, in England, apples and pears ripen in Autumn, so this would indicate that the "unripe fruits" which are "clad in one green hue" are the result of the summer growth that will only ripen with the onset of autumn. Another clue is that it is not actually raining. Summer is the one season where you might be lucky enough to have a rain-free day in Britain, though don't count on it! These two indications suggest that the season is summer.