This page is using eclipsed speculation about his wives [28 March 2010]
There is a very detailed article in Source:The American Genealogist, p. 30:155, "The Salem Gardners:Comments and Clues" by George E. McCracken. My notes are sketchy as I was interested mostly in George's father, but there is a extensive discussion on George's three wives. After literally pages of detailed reasoning and evidence, the conclusion is that his wives are 1) Hannah ---, mother of the eldest three children; 2) Elizabeth Freestone, widow of Robert Turner, and mother of the remaining five children; 3) Elizabeth Allen, widow of Rev. Samuel Stone.
Of the three, Elizabeth (Allen) Stone is the only one currently listed on the page. Trying to be brief, though I may miss many subtleties: Both Elizabeth Allen and Elizabeth Horne lived longer than George, so they are mutually exclusive. The will of Elizabeth Gardner names her son Samuel Stone, and so it was Elizabeth (Allen) Stone. Since Elizabeth Gardner's will names no Gardner children, the Elizabeth who named as the mother of five Gardner children is not her, but the previous wife, the widow Turner. No Ruth Turner can be found, leading to Elizabeth (Freestone) Turner. The first wife is never named in the birth records, but appears to be yet another wife on the assumption incest wouldn't be allowed, and as the eldest daughter was named Hannah, and a Hannah Gardener joined the church a few years after George did, it is assumed the first wife was Hannah ----.
It is often thought the Hannah Gardener that joined the church was Thomas Jr.'s first wife. That made sense when there was an alternative for George, but given the above rejection of supposed wives, it doesn't fit well, since Thomas Jr. starting baptizing children in 1643 and Hannah Gardener wasn't admitted until 1649. It appears we still know nothing about Thomas Jr.'s first wife.
The inclusion of Elizabeth Horne was due to reference in Deacon John Horne's will of 1679 to his daughter Elizabeth Gardner. If she is not George's wife, how to explain that? George's brother Samuel married Elizabeth, widow of John Paine, creating an Elizabeth Gardner, but not until 1680, so too late to qualify. The suggestion by Source:Gardner, Frank A. Thomas Gardner, Planter, and Some of His Descendants is that Elizabeth Gardner is Thomas Gardner, Jr.'s second wife, who was known to be named Elizabeth, thereby accounting for Elizabeth Horne.
The article mentioned is cited in the Great Migration Begins as the authority for its identification of the wives of George and Thomas, Jr. --Jrich 23:27, 9 January 2009 (EST)