Sorry I didn't see this until now.

I've worked in a number of historic forts for the National Park Service, some of them places that had forts at one time that still retain some of the old functional names. I haven't worked at any castles, but it would apply there as well.

The Sally Port is the back or postern gate out of a fort or fortified place (like a castle); when I worked at the Statue of Liberty (atop the old star-shaped Fort Wood), the sally port was the smaller back door we used to take people out if we didn't want to go through the big front doors. A door like that is secure, and while it is strategic for sending out troops when needed in a fight, is useful for when you're living and working in a fort and want to work on the grounds around the outside of it. Like in the garden. There was one of those at San Juan Island NHP also, in English camp, if I recall correctly. If you don't have room inside for a kitchen garden, it's practical that it be close to the fort walls, and near the door into the domestic area of the fort, etc.

To see the sally port at the Statue of Liberty (Fort Wood when it was there alone with no pedestal or statue) get the movie Splash. When Darryl Hannah comes ashore in NYC to find the Tom Hanks character they pretend it is the front entrance to the statue, but it was actually filmed at the sally port (they just closed part of the island for filming, but they didn't close the island to visitors). She has his wallet with her, and arrives nude on the grounds at the statue. Ron Howard's folks didn't tell the NPS that there was nudity in the scene--that freaked them out a little.

So, the sally garden in that context is the kitchen garden or it could be a pleasure garden outside the alternate exit from the fort. In skimming all of the discussion above about sally gardens in various localities I didn't see anything that would suggest that there wasn't a fort or castle nearby that had a sally port that gave the garden it's name. I'd be willing to bet real money that the terms sally port and sally garden were in use for a long time in the UK or Europe before they made their way over here, possibly as artifacts of activities that happened in a given area long time ago. In communities that had some history of an old fortified structure, it makes sense that there are a few sally gardens around the English-speaking world.

I sounds to me like grasping at straws to convert salix (willow) to give the name to the garden. It just doesn't make sense. I have the impression that willow is more likely to be called withy rather than sally.

SRS