| Cultivar Name | Plant Size | Origin | Flower Color | Season | Source | Registered |
| 'Cabin Fever' | Large | Hybrid | - | - | Christensen, John | --NR-- |
| 'Caid Man' | Large | Hybrid | Near-White | July | Heinz, Jim | --NR-- |
| 'Cally Atom' | Miniature | Unknown | Pale-Lavender | July | Wickenden, Michael | --NR-- |
| 'Cambria Blue' | Medium | Unknown | - | - | Benedict, Dr Ralph (Herb) | --NR-- |
| 'Camelot' | Medium | Unknown | Pale-Lavender | July | Smith, Eric & British Hosta and Hemerocallis Society | .1988 |
| 'Canadian Blue' | Large | Unknown | Pale-Lavender | July into August | Van Vliet, Arie & Walek, Kevin | .2009 |
| 'Candelabra' | Small | Unknown | Light-Purple | July into August | Benedict, Dr Ralph (Herb) & Walek, Kevin | .2009 |
| 'Candy Hearts' | Medium | Hybrid | Pale-Lavender | July | Fisher, Eunice V. & Ruh, Peter | .1998 |
| 'Capricorn' | Large | Hybrid | - | June into July | Husemann, Jim | .2009 |
| 'Captain's Canopy' | Large | Unknown | - | - | Seaver, Charles | --NR-- |
| 'Carder Blue' | Medium | Unknown | Near-White | June into July | Carder, Ellen & The American Hosta Society | .1986 |
| 'Cardiac' | Large | Unknown | - | - | Asch, Stuart | --NR-- |
| 'Carl' | Small | Unknown | Pale-Lavender | June into July | Calderara, Carl & Ruh, Peter | .1991 |
| 'Carolina Blue' | Medium | Hybrid | Light-Purple | August | Solberg, Robert | .2000 |
| 'Catherine Ann' | Medium | Hybrid | Pale-Lavender | June | Nyikos, Frank | .1999 |
| 'Centennial' | Giant | Unknown | - | - | Ward, Dr Dick & Ward, Jane | .1996 |
| 'Century One' | Large | Hybrid | Near-White | June into July | Moldovan, Steve | .1983 |
| 'Cerulean Lagoon' | Large | Unknown | - | - | Serafin, Viktoria | --NR-- |
| 'Cerulean Magic' | Medium | Hybrid | - | June into July | Zilis, Mark | .2009 |
| 'Chances Are' | Giant | Unknown | Near-White | June into July | Tompkins, Chet & Walek, Kevin | .2010 |
| 'Change of Venue' | Large | Sport | Near-White | June into July | Lysne, Rod | .2019 |
| 'Charlebois' | Large | Hybrid | Pale-Lavender | - | Bastille, Jocelyne | --NR-- |
| 'Charlie Jane' | Giant | Hybrid | Near-White | June into July | Kwick, Charles | .2018 |
| 'Chart Topper' | Medium | Sport | Pale-Lavender | July into August | Zilis, Mark | --NR-- |
| 'Chesapeake Bay' | Large | Hybrid | Near-White | July | Petryszyn, Olga | .2004 |
| 'Chickasaw' | Large | Unknown | - | - | Wade, Van | --NR-- |
| 'Chief Crazy Horse' | Giant | Unknown | - | - | Wade, Van | --NR-- |
| 'Chief Killbuck' | Giant | Unknown | - | - | Wade, Van | --NR-- |
| 'Chief Little Turtle' | Giant | Unknown | - | - | Wade, Van | --NR-- |
| 'Chief Sitting Bull' | Giant | Unknown | - | - | Wade, Van | --NR-- |
| 'Chief Thundercloud' | Giant | Hybrid | - | - | Wade, Van | --NR-- |
| 'Chief White Cloud' | Giant | Hybrid | Pale-Lavender | August | Wade, Van | .2007 |
| 'Chiemsee Blaue Taube' | Medium | Sport | Med-Lavender | - | Eschenbach, Volker | --NR-- |
| 'Chiemsee Madonna' | Small | Sport | Med-Lavender | June into July | Eschenbach, Volker | --NR-- |
| 'Chiemsee Schätzchen' | Medium | Sport | Pale-Lavender | July into August | Eschenbach, Volker | --NR-- |
| 'Childhood Fantasy' | Medium | Hybrid | - | - | Livingston, Ron | --NR-- |
| 'Chippewa' (Wade) | Giant | Hybrid | Pale-Lavender | July into August | Wade, Van | --NR-- |
| 'Chivalry' | Medium | Hybrid | Med-Lavender | July into August | Malloy, Alex | .2001 |
| 'Choctaw' | Giant | Hybrid | Near-White | June into July | Wade, Van | .2007 |
| 'Chodai Ginyo' | Large | Sport | Med-Lavender | July into August | Unknown | --NR-- |
| 'Chopstick Bridge' | Large | Hybrid | - | - | Stadden, Josh | --NR-- |
| 'Christopher Wayne' | Large | Unknown | - | - | Aden, Paul | --NR-- |
| 'Civil War' | Large | Unknown | Near-White | July | Freeman, Franc & Freeman, Sally | .2008 |
| 'Clambake' | Large | Hybrid | Pale-Lavender | July into August | Goodwin, Randy | .2000 |
| 'Clap Your Hands' | Large | Hybrid | Pure-White | June into July | Dalton, Jim & Dalton, Meg | .2012 |
| 'Clarence' | Medium | Hybrid | Near-White | June into July | Simpers, Lucille | .1996 |
| 'Classic Delight' | Giant | Hybrid | Pale-Lavender | July | Fisher, Eunice V. | .1973 |
| 'Clattering Water' | Medium | Sport | Med-Lavender | - | Fransen, Marco & Fransen, Joyce | --NR-- |
| 'Clayton Burkey' | Large | Unknown | Near-White | July | Burkey, Clayton & Zolock, Steve & Zolock, Sarah | .2005 |
| 'Clear Fork Blue' | Giant | Unknown | Pale-Lavender | June into July | Wade, Van | --NR-- |
| 'Clem Kadiddlehopper' | Large | Unknown | Pale-Lavender | - | Sawyer, Rick | --NR-- |
| 'Cloudburst' | Medium | Hybrid | Light-Purple | July | Beilstein, Doug & Zilis, Mark | .2006 |
| 'Clouded Skies' | Medium | Hybrid | Med-Lavender | July into August | Avent, Tony | .2007 |
| 'Cobblestones' | Giant | Unknown | Near-White | June into July | Ward, Dr Dick & Ward, Jane | .2012 |
| 'Cobra's Lair' | Medium | Hybrid | - | - | Philips, Hugo | .2010 |
| 'Colesburg Blue' | Medium | Hybrid | Pale-Lavender | June | Hackbarth, Robert | .2004 |
| 'Collector's Dream' | Large | Sport | Near-White | June into July | Janssen, Bill | --NR-- |
| 'College' | Large | Unknown | - | - | Fransen, Marco | --NR-- |
| 'Colonel Murphy' | Giant | Unknown | Med-Lavender | July into September | Zolock, Steve & Zolock, Sarah | .2001 |
| 'Colossal' | Giant | Unknown | Pale-Lavender | June | Savory, Robert | .1977 |
| 'Comanche' | Large | Sport | Near-White | June into July | Wade, Van | --NR-- |
| 'Connecticut River' | Medium | Hybrid | Pale-Lavender | - | Beilstein, Doug & Malloy, Alex | .2005 |
| 'Conquistador' | Large | Hybrid | Light-Purple | July into August | Livingston, Ron | --NR-- |
| 'Contort' | Large | Unknown | - | - | Livingston, Ron | --NR-- |
| 'Contorted Dragon' | Large | Hybrid | - | - | Livingston, Ron | --NR-- |
| 'Conundrum' | Giant | Unknown | Med-Lavender | June into July | Gilligan, Madelon | .2012 |
| 'Cool Blue' | Medium | Unknown | Med-Lavender | June into July | Benedict, Dr Ralph (Herb) & Benedict, Dorothy & Kuenster, Rod | --NR-- |
| 'Cool Dreams' | Medium | Hybrid | Pale-Lavender | June into July | Zilis, Mark | .2010 |
| 'Cool Waters' | Medium | Hybrid | Light-Purple | June into July | Zilis, Mark | .2010 |
| 'Cooltini' | Small | Hybrid | Light-Purple | August to September | Zilis, Mark | .2009 |
| 'Cornerstone' | Giant | Hybrid | Near-White | July | Hanna, Clarence | .2013 |
| 'Corryvreckan' | Medium | Unknown | - | - | Black, Gwen | --NR-- |
| 'Cortland' | Large | Unknown | - | - | Unknown | --NR-- |
| 'Cosmic Blue' | Medium | Hybrid | Med-Lavender | - | Livingston, Ron | --NR-- |
| 'Cosmic Moon' | Large | Hybrid | Near-White | July into August | Kuenster, Rod | .2015 |
| 'Country Dreaming' | Large | Hybrid | Pale-Lavender | July | Dean, Don | .2013 |
| 'Country Rippled Relic' | Medium | Hybrid | Med-Lavender | July into August | Dean, Don | .2019 |
| 'Coventry' | Medium | Unknown | - | - | Minks, Eldren | --NR-- |
| 'Crater Lake' | Large | Hybrid | Near-White | June into July | Snyder, Ron | .1996 |
| 'Crazy Mouse' | Small | Hybrid | - | - | Avent, Tony | --NR-- |
| 'Cree' | Giant | Hybrid | Near-White | June into July | Wade, Van | .2007 |
| 'Creek' | Medium | Hybrid | Pure-White | June | Wade, Van | .2007 |
| 'Crescendo' | Large | Hybrid | Near-White | June into July | Kamp, Gayle | .2001 |
| 'Crinkled Joy' | Large | Unknown | Near-White | July | Unknown | --NR-- |
| 'Crinkled Leather' | Large | Hybrid | Pale-Lavender | July into August | Dean, Don | .2014 |
| 'Crinoline Petticoats' | Giant | Hybrid | Near-White | June into July | Soules, Clarence | .1990 |
| 'Crossroads Budgie' | Small | Hybrid | Med-Lavender | July | England, Tim | .2003 |
| 'Cubra Libra' | Large | Unknown | - | - | Livingston, Ron | --NR-- |
| 'Cup of Glory' | Giant | Unknown | - | - | Bastille, Jocelyne | --NR-- |
| 'Curlew' | Large | Unknown | Pale-Lavender | August to October | Smith, Eric & British Hosta and Hemerocallis Society | .1988 |
| 'Curtain Call' | Medium | Sport | Light-Purple | July into August | Wilkins, Dr Jim | .1998 |
| 'Curtis Sutton' | Large | Hybrid | Pale-Lavender | June into July | Powell, Loleta | --NR-- |
| 'Cutie' | Medium | Unknown | Med-Lavender | August to October | Benedict, Dr Ralph (Herb) & Kuenster, Rod | .2010 |
| 'Cutting Edge' | Large | Hybrid | Pale-Lavender | July into August | Benedict, Dr Ralph (Herb) & Gowen, Hideko | .1999 |
| 'Cyclops' (Soucek) | Giant | Unknown | Near-White | July into August | Soucek, Rachel | --NR-- |
| 'Cyclops' (Tompkins) | Large | Unknown | - | - | Tompkins, Chet | --NR-- |
|