| Cultivar Name | Plant Size | Origin | Flower Color | Season | Source | Registered |
| 'Cabin Boy' | Medium | Hybrid | Light-Purple | July into August | Kwick, Charles | .2017 |
| 'Canadian Foreign Affairs' | Giant | Unknown | Pale-Lavender | July into August | Knechtel, Ken & Ruh, Peter | .2002 |
| 'Capitol Dome' | Medium | Hybrid | - | - | Minks, Eldren | .1980 |
| 'Carefree' | Large | Hybrid | Pale-Lavender | July | Fisher, Eunice V. | .1971 |
| 'Carol Marie' | Miniature | Hybrid | - | June into July | Kwick, Charles | .2016 |
| 'Cathedral of Learning' | Large | Unknown | Med-Lavender | July into August | Zolock, Steve & Zolock, Sarah | .2007 |
| 'Catherine the Great' | Medium | Unknown | Pale-Lavender | July into August | Goodwin, Randy | .2019 |
| 'Ceres' | Small | Unknown | - | - | Malloy, Alex | --NR-- |
| 'Cerveza' | Large | TC Sport | Med-Lavender | August | Zilis, Mark | .2009 |
| 'Charm' | Small | Unknown | - | - | Unknown | --NR-- |
| 'Chartreuse Ruffles' | - | Unknown | - | - | Summers, Alex | --NR-- |
| 'Chartreuse Spoons' | Medium | Unknown | Pale-Lavender | July into August | Livingston, Ron | --NR-- |
| 'Cheese Ball' | Miniature | Unknown | Pale-Lavender | July into August | Goodwin, Randy | .2017 |
| 'Cheese Louise' | Large | Unknown | - | - | Hackbarth, Robert | .2015 |
| 'Cheesehead' | Large | Unknown | - | - | Zilis, Mark | --NR-- |
| 'Chicken' | Medium | Unknown | - | - | Belk, Al | --NR-- |
| 'Chickenhearted' | Medium | Hybrid | Pure-White | July into August | Groothuis, Mike | .2012 |
| 'China Doll' | Small | Hybrid | Pure-White | July into August | Savory, Robert | .1988 |
| 'Chirp' | Miniature | Sport | Light-Purple | July | Zilis, Mark | --NR-- |
| 'Chris' China Star' | Medium | Hybrid | - | - | Brinkmann, Christina | --NR-- |
| 'Christmas Dome' | Large | Unknown | - | - | Livingston, Ron | --NR-- |
| 'Ciandra' | Giant | Hybrid | Pure-White | June into July | Schulz, Ed | .2017 |
| 'Clean Green' | Medium | Hybrid | Pure-White | July into August | Goodenough, Rick & Gilligan, Madelon | .2017 |
| 'Cloud Lime' | Medium | Unknown | - | - | Serafin, Viktoria | --NR-- |
| 'Cold Heart' | Large | Unknown | Pale-Lavender | June into July | Scheer, Alttara & The American Hosta Society | .2019 |
| 'Color Parade' | Medium | TC Sport | Pale-Lavender | August | Zilis, Mark | .2003 |
| 'Contender' | Large | Unknown | - | - | Aden, Paul | --NR-- |
| 'Country Melody' | Large | Hybrid | Near-White | July into August | Dean, Don | .2013 |
| 'Cousin Lou Ann' | Large | Unknown | - | June into July | Zilis, Mark | .2010 |
| 'Cranberry Wine' | Small | Hybrid | - | - | Sisson, Kathie | --NR-- |
| 'Creamsicle' | Medium | Unknown | - | - | Purvis, Owen & Purvis, Sue | --NR-- |
| 'Crows Landing Fairy Ghost' | Medium | Unknown | - | - | Stygall, Patsy | .2011 |
| 'Curly Fries' | Medium | Hybrid | Deep-Purple | August | Solberg, Robert | .2008 |
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