Usually in literature spring represents rebirth, new beginnings, resurrection etc. Summer sometimes is symbolic of passion because of the heat.
I agree with the rebirth and new beginnings but perhaps Summer could be like growth and strength? In Summer, the sun kills a lot of the pretty flowers and only the strong ones survive along with the grass and plants, but even the grass can die if the sun is too strong... YES
Summer could also represent the height of your life: hot weather, vacations, more freedom, and overall happiness.
