The Onam floral carpet, known as Onapookkalam or just Pookkalam, is made out of the gathered blossoms with several varieties of flowers of differing tints pinched up into little pieces to design and decorate patterns on floor, particularly at entrances and temple premises like a flower mat. Lamps are arranged in the middle or edges. It is a work of religious art, typically the team initiative of girls and women, who accomplish it with a delicate touch and a personal artistic sense of tone and blending.[34] When completed, a miniature pandal (umbrella) hung with little festoons is erected over it. The pookkalam is similar to Rangoli which is made of powders of various colors and is popular in North India.

The traditional ritual of laying pookkalam (floral carpet) starts on Atham day. The pookkalam on this day is called Athapoo, and it is relatively small in size. The size of the pookkalam grows in size progressively with each day of the Onam festival. Only yellow flowers will be used on Atham with only one circular layer made and the design is kept simple. Statues or figurines of Mahabali and Vamana are also installed at the entrance of each house on this day.[citation needed]

Traditionally, Atthapookalams included flowers endemic to Kerala and the Dashapushpam (10-flowers), but nowadays all varieties of flowers are used. Earthen mounds, which look somewhat like square pyramids, representing Mahabali and Vamana are placed in the dung-plastered courtyards in front of the house along with the Pookalam, and beautifully decorated with flowers. All over Kerala, Pookalam competitions are a common sight on Onam day.