fertile period
fertile phase

This was a fertile period in the visual arts.

The couple then abstains from intercourse during the fertile period.

And no previous exhibition has ever tried to bring together the work created in this fertile period.

Well, can't you estimate your fertile period and avoid it?

But perhaps the most fertile period of invention was the late 20th century.

His most fertile period was between 1833 and 1850.

The decade from 1880 to 1891 was the most fertile period of Maupassant's life.

The industry, he said, is entering its most fertile period since the 1920's, when radio and talking pictures exploded onto the scene.