Bonnie I would use a combination of fishing line or florist wire for tying the grapevine together at certain points but then hang it from 3M removable small white hooks that you affix temporarily to your mantle.
Annie Thornton The blue color is Woodlawn Blue by Benjamin Moore. If you click "More Info" a little green product tag with the color info has been added to this image.
Karla from The Little Things that Makes a House a Home blog used a grapevine garland to create a beautiful rustic mantel decor:
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