1860 in Thoreau’s Journal:

It is truly June when you begin to see brakes (dark green) fully expanded in the wood paths.  In early June, methinks as now, we have clearer days, less haze, more or less breeze, especially after rain, and more sparkling water, than before.  I look from Fair Haven Hill….The leaves generally are almost fully expanded….

1850 in Thoreau’s Journal:

Not till June can the grass be said to be waving in the fields. When the frogs dream and the grass waves, and the buttercups toss their heads, and the heat imposes one to bathe in the ponds and streams, then is summer begun.