That depends on where you live.
In California, plant growth is mostly limited
by the availability of water, which means that the
growing seasons run from mid-winter to early
summer. In deserts where winters are cold, plants
grow most after the thaw, in early spring, but
before the desert can dry up. In most other
places, plants grow more in summer either because
it's too cold in winter (northern/southern
climates) or because the summer is when the rains
come (tropical climates).