Bottlebrush.  Perhaps the hardiest clone enduring single digits with scarcely a whimper.  (It may be whimpering but my own wails of despair drown all else out).  Evergreen picking up russet tones in winter.  Summer fuzzy red flowers on the stems.  Deer Proof/drought tolerant.

Fun and very hardy selection that has willowy and twisting branchlets sporting 2" light yellow flower brushes on the branch tips all pointing willy-nilly for wild Medusal effect with a long bloom period on older plants.  Happy in nearly any soil and happiest with regular water.  Not deer fodder.

One of the hardiest Bottlebrushes to 10F with the added benefit of having red flowers. In growth, this this tends to have graceful arching branches which softens what can sometimes be a rigid look to Callistemon.  Not that that is a bad thing but this looks a bit more cuddly.  This grows on stream banks in Australia and can take quite wet spots but is also tolerant of dry.  Deer proof!

This clone of an already hardy bottlebrush species has been hardier than
the typical offering by a few degrees and personally, our most grievous
losses have been by a few degrees.  This is likely from a higher and
more exposed location in Tasmania as it is also more compact than
typical and has handled one winter where it went into single digits.