Also known as Pushpadolotsav - Festival of Flowers, it is celebrated on the day after Holi, on Fagun
Vad 1.

Origin
Once Arjun accompanied Shri Krishna to Raivatachal - Mt.Girnar. Here the Lord pleased the Yadavas with divine sports. In turn, to please him, the joyous Yadavas made a swing of flowers. They then seated Shri Krishna and Arjun on the hindolo (swing), performed pujan and swung the hindolo. Henceforth the two became renowned as Nar-Narayan and the Pushpadolotsav came into being.

Import
By performing actions in accordance to the rules of Dharma, to please the Lord, the devotee symbolically brings the Lord nearer his heart. This is akin to pulling the hindolo swing towards himself. When the devotee falters in his devotion, the Lord moves away, symbolised by the swing moving away. Therefore the devotee strives to offer better bhakti, which results in the Lord's incessant proximity.

Ritual
Devotees construct a hindolo of flowers, instal the Lord's murti and swing Him. They also spray colored water on each other.

On Fuldol, people traditionally offer fagwaa roasted chick peas (chana), dates and popcorn to God and partake of the prasad.

In the Swaminarayan Sampraday, the women devotees of north Gujarat requested Bhagwan Swaminarayan for unique fagwaa in the Fuldol of Samvat 1868 (1812 CE), in Sarangpur. It comprised lofty sentiments in the form of a prayer to be delivered from maya:
Maha balvant maya tamaari, jene aawariya narnaari...
The prayer, versified by Nishkulanand Swami in the Bhaktachintamani (ch.64), is sung regularly even today.

Bhagwan Swaminarayan celebrated Fuldol in many different places during His period. Of these, the two most prominent were in Samvat 1872 (1816 CE), in Vartal and in Samvat 1868 (1812 CE), in Sarangpur. Pramukh Swami Maharaj celebrates this festival on a huge scale in Sarangpur in Saurashtra, with devotion and fervor.

In the Swaminarayan Sampradaya's shikharbaddh mandirs, Fuldol is traditionally celebrated with immense fervor after the Rajbhog Arti, around 11 a.m. A water hose attached to Bhagwan Swaminarayan's murti in the central shrine sprays colored and fragrant water on the devotees. Besides being solaced they feel spiritually charged in being graced with sanctified water by God.