- Cambridge (s) - Pale blue. Colledge, 1964.
- Camilla (s) - Lavender.
- Can-Can (s) - Rose pink.
- Candy (s) - An older maroon stripe sweet pea; flowers rather small by modern standards.
- Candy Frills (s) - Lavender.
- Caprice (s) - Blue. 1975.
- Captain Lewin (s) - Glossy maroon, superceded by Burnished Bronze. Harrod.
- Captain of the Blues (g) - Mid blue. Echford, 1891.
- Captain Scott (s) - White. 1981.
- Cara Hepworth (s) - Orange-red. 2001.
- Carlotta (s) - Magenta. Carter, 1937.
- Carmen (e) - A carmine rose EMG variety.
- Carnival Queen (s) - Magenta. 2004.
- Carol (e) - A pink Cuthbertson Florabunda variety. Cuthbertson.
- Cascade (e) - A white Spencer Praecox sweet pea.
- Castle of Mey (s) - A rich cream sweet pea considered inferior to Jilly for exhibition. 2001.
- Castlewellan (s) - Salmon pink on cream ground, aka Harlow Carr. Harrod.
- Catherine (e) - A cerise Cuthbertson Florabunda sweet pea. Cuthbertson.
- Catherine (s) - Orange-red. 1985.
- Cathy Wright (s) - An impressive pure white exhibition sweet pea. 2000.
- CCC (g) - A white modern grandiflora sweet pea. Grayson, 1998.
- Celebration (g) - A series of frilly grandiflora type sweet peas. Brackley, 1993.
- Celia (s) - Magenta. 2006.
- Challenger (s) - Mauve.
- Champagne Bubbles (s) - Salmon pink.
- Chance (s) - Red/magenta bicolour. Parsons, 2006.
- Charisma (s) - Carmine. 1993.
- Charles Unwin (s) - Salmon pink on cream ground. Colledge, 1985.
- Charley Paige (s) - Pink stripe on white. 2008.
- Charlie (s) - Deep violet-maroon. 2003
- Charlie's Angel (s) - A large flowered light blue sweet pea. Hanmer, 1990.
- Charlotte Emma (s) - Pink. Kerton, 2009.
- Charlotte Ryley (g) - A violet old fashiond sweet pea. Grayson, 1997.
- Chatsworth (s) - Pale blue. 1998.
- Cheshire Dark Blue (g) - A purple- blue grandiflora type sweet pea of uncertain origin.
- Chloe (e) - A deep purple EMG variety.
- Chris Harrod (s) - Light blue. Harrod, 2008.
- Cirrus (s) - Pink stripe. Tullet, 2004
- Claire Elizabeth (s) - Picotee on white ground.
- Colin Unwin (s) - Cerise.
- Coline (e) - A Cuthbertson Florabunda sweet pea variously described as cerise or scarlet. Cuthbertson.
- Colleen Mary (s) - Salmon pink on cream. Tierney, 2008.
- Columbus - A pale blue multiflora sweet pea. Unwin, 1993.
- Comet (s) - Carmine. Dobbie, 1964.
- Comet (s) - Light pink stripe. Unwin, 1998.
- Concorde - Bright carmine rose. 1981.
- Connie (e) - A deep rose pink Cuthbertson Florabunda sweet pea. Cuthbertson.
- Cooltonagh Pink - A small flowered pink sweet pea which is not sunproof. Harrod.
- Coquette (e) - A picotee EMG variety.
- Coraleena (s) - Scarlet cerise. Harrod, 2009.
- Corinne (s) - An older carmine sweet pea.
- Countess Cadogan (g) - Rich violet-blue. Eckford, 1899.
- Countess Spencer (s) - The original sport from the grandiflora 'Prima Donna', from which all modern Spencer sweet peas are descended.
- Cream Beauty (s) - Cream.
- Cream Cracker (s) - Cream. Wells, 2005.
- Cream Elegance (s) - Cream.
- Cream Southbourne (s) - A cream sport from the pale pink Southbourne. Colledge, 1982.
- Cream Triumph (s) - Cream.
- Cupani - Intense maroon/violet bicolour. The original wild sweet pea. 1699.
- Curbar Edge (s) - Rose pink on a cream ground.
- Cuthbertson Florabunda (e) - An American spring flowering series of sweet peas. Cuthbertson, 1940s.
- Cyril Fletcher (s) - Rose pink. 1984.
- Cyril Plater (s) - Rosy mauve. Kerton.