Now in its third year, the annual Green Apple Music Festival expanded to eight cities, safely staking its claim as the world's largest Earth Day celebration. As in years past, the multi-day gathering, organized by Peter Shapiro and Relix/Jambands.com parent company Zenbu Media, presented a number of free shows in parks throughout the country and greened prominent music clubs in each participating city.

While Green Apple grew out of New York, this year’s flagship festivities took place at Washington, DC’s National Mall, where an eclectic mix of bands, entertainers and prominent political figures discussed the importance of “living green.” Though severe lightning cut the day’s festivities short, many fans faced the inclement weather to see O.A.R. deliver a rare acoustic set and Warren Haynes perform a few solo songs, including U2’s “One.” Actor/comedian Chevy Chase, who actually played in an early incarnation of Steely Dan, also addressed the crowd and introduced Haynes.

Meanwhile in Chicago, 3, the new trio featuring Grateful Dead drummer Bill Kreutzmann, Allman Brothers Band bassist Oteil Burbridge and Max Creek guitarist Scott Murawski, headlined a day long event at the Lincoln Park Zoo. Over 40,000 people showed up throughout the afternoon to take in additional performances by Dirty Dozen Brass Band, Meshell Ndegeocello, Bassnectar, the Chicago Afrobeat Project and The Gwalla Gwallas. For their set, Kreutzmann, Burbridge and Murawski relied heavily on the Grateful Dead canon, delivering reworked renditions of “Estimated Prophet,” “U.S. Blues,” “Eyes of the World,” “Turn on Your Lovelight” and “The Other One,” among others. At night, 3 also delivered its second-ever club performance at the intimate Martyrs.

Green Apple’s New York offerings doubled as the kickoff party to the Central Park concert season. Bluegrass legends Ricky Skaggs & Kentucky Thunder capped off an action packed day at the park’s Rumsey Playfield with what Skaggs’ jokingly described as a “completely green,” meaning unplugged performance. Other acts included Vusi Mahlasela, Big Head Todd and the Monsters, The Bacon Brothers, Vienna Teng and event MCs Annabelle Gurwitch (Discovery Network) and Graham Hill (Treehugger). Vusi Mahlasela surprised many fans by inviting out fiddler Ann Marie Calhoun, who has used her recent My Grammy’s Moment win to score spots onstage with the likes of the Disco Biscuits and Yonder Mountain String Band.

Meanwhile, on Friday and Saturday, Tea Leaf Green held court at the Highline Ballroom with special guests Hot Buttered Rum and Moonalice, while RAQ headlined the Blender Theater with the aid of The Pnuma Trio and Jounce. In the special guest department, Hot Buttered Rum’s Aaron Redner sat in with TLG on a cover of The Band’s “Ophelia” and “Criminal Intent,” a night before Moonalice’s Barry Sless and Pete Sears performed with the quartet on “I've Got a Truck.” Later in the weekend, Surprise Me Mr. Davis, the union of The Slip and Nathan Moore, closed out the festival on Sunday with a performance at Sullivan Hall.

Undoubtedly one of Green Apple’s highlights was at San Francisco’s Golden Gate Park. The day kicked off with performances by Brett Dennen, Dan Licks & the Hot Licks with special guest Michael Kang and Yonder Mountain String Band. Surprise guest Bob Weir then joined Mickey Hart for an acoustic cover of The Beatles’ “Blackbird,” before String Cheese Incident’s Michael Kang and Yonder Mountain’s Ben Kaufmann joined the Grateful Dead duo for takes on “Peggy-O” and “Friend of the Devil.” The latter song eventually gave way to a freeform that drew in Joan Baez as well. Hart’s mass drum segment then morphed several times and featured an incredibly eclectic mix of musicians, including Jon Fishman, Tommy Lee, Sikiru Adepoju, Bobi Cespedes, Rebecca Mauleon, Rhythm Village and Loco Bloco. At the end of the improvisation, the all-star cast segued into a show closing version of “Not Fade Away,” which ended with Weir, Hart, Lee, Kang and Baez reclaiming the stage to finish the popular Buddy Holly cover. Later in the evening, Kang, Steve Molitz(Particle, Phil Lesh & Friends), Aaron Holstein (Vibesquad, Zilla), Kevin 'KJ' Sawka, Jamie Janover (Zilla, Sporque), Sasha Rose (aka Sasha Butterfly) and Audio Angel closed out the weekend’s festivities with a Symbiotic Orchestra performance at 1015 Folsom.

Green Apple also hosted events this weekend in Miami, Los Angeles, Denver and Dallas. Portions of the weekend’s festivities will be broadcast on MySpace Tuesday night.