Why Wednesday specifically
Wednesday (Budhvar) is named for Budh, the planet Mercury, associated with intellect, communication and new beginnings. This pairs naturally with Ganesha, who is invoked at the start of any new venture and worshipped as the remover of obstacles (Vighnaharta) — qualities closely tied to the mental clarity and fresh starts Mercury represents.
How the day is typically observed
Many devotees visit a Ganesha temple on Wednesday, offer durva grass and modak, and recite the Ganesh Chalisa or a Ganesh mantra. It's considered an auspicious day to begin new work, sign agreements, or start learning something new, precisely because of Ganesha's association with removing obstacles at the outset.
Budh Grah and Wednesday
Beyond Ganesha, Wednesday is also linked to Budh (Mercury) in Vedic astrology, and those wanting to strengthen a weak Mercury in their birth chart are sometimes advised to observe specific Wednesday practices, such as donating green items or reciting Budh-related mantras — though this is a separate, more specialised tradition from the general Ganesha worship most households observe.
A gentle midweek anchor
Falling in the middle of the week, Wednesday's Ganesha worship offers a natural pause — a moment to clear mental clutter and start the second half of the week with the same clean-slate spirit Ganesha represents at the start of any undertaking.