Since a garland is in circular shape, circular permutation is used.
4 flowers are to be together.
$\therefore$ they are to be considered to be one.
Hence there are 5 different type of flowers.
They can be arranged in a circle in $4!$ ways.
But these 4 flowers that are together can be arranged among themselves in $4!$ ways.
$\therefore$ The required no. of arrangements $= 4!.4!$