- Macmillan Nurse (s) - Rose pink. 1996.
- Maestro (s) - Lavender. B.R.Jones/Beane/Cave, 2009.
- Maggie May (s) - Blue flush on cream. 1978.
- Magic (s) - Salmon pink on cream.
- Magnificent Mauve (s) - A very large flowered mauve sweet pea. Harrod.
- Majesty (s) - White.
- Marbled Purple (g) - Purple flake sweet pea, aka The Major. Turral, 1960s.
- Margaret (e) - A deep rose EMG sweet pea.
- Margaret (s) - Orange pink. Spectacular, but did not breed true. 2004.
- Margaret Joyce (s) - Mid blue. Robertson, 1996.
- Margaret Hughson (s) - Pink / white bicolour sweet pea. Chisholm, 2008.
- Margot (s) - Cream.
- Marguerite (s) - Lavender.
- Marilyn (e) - A scarlet cerise EMG sweet pea.
- Mariner (e) - A blue Spencer Praecox variety.
- Marion (e) - A cream Cuthbertson Florabunda variety. Cuthbertson.
- Marion (s) - An reliable older lavender sweet pea, recognisable by the darker veining in the petals.
- Mark Harrod (s) - Scarlet. Harrod, 2007.
- Marmalade Sky (s) - Orange-red stripe. 1997.
- Maroon Magic (s) - Maroon. 1993.
- Mars (s) - A dramatic red stripe. 1996.
- Martha Lane Fox (s) - Scarlet. 2001.
- Marti Caine (s) - Crimson. 1996.
- Mary Cynthia (s) - Cream flushed on salmon. 2010.
- Mary Malcolm (s) - A famous old sweet pea prized for its delicate apricot salmon colour. Not sunproof.
- Mary Rose (s) - Rose pink. 1997.
- Matucana (g) - Maroon/purple bicolour from Peru. Harland, 1950s.
- Maudie Best (s) - Maroon.
- Maudie Winfield (s) - Maroon.
- Mauve King (s) - Mauve.
- Mauve Queen (g) - Mauve standard with bluish mauve wings. Eckford, 1887.
- Maytime (s) - Rose pink.
- Memorial Flight (s) - A strongly scented pure white sweet pea. King, 1998.
- Memories (s) - Rose pink.
- Memory (e) - A lavender Spencer Praecox variety.
- Midnight (s) - An old maroon sweet pea, now surpassed by Burnished Bronze and Windsor. B.R.Jones, 1986.
- Milestone (s) - Maroon.
- Millennium (s) - A rich crimson sweet pea; the best variety of this colour. D.M.Jones, 2000.
- Milly (s) - Magenta. 2007.
- Minnie (e) - A navy blue EMG sweet pea.
- Min's Ambition (s) - Magenta. Woodcock, 1993.
- Miranda (e) - A crimson EMG.
- Miranda Crafer (s) - Magenta. Walker, 1996.
- Miss Truslove (s) - A pale mauve sweet pea. Truslove.
- Miss Willmott (g) - Salmon-pink standard with salmon-rose wings. Eckford, 1901.
- Misty (s) - Mauve flush. Leese, 2008.
- Misty Mountain (s) - Pale mauve. 2004.
- MM (s) - Cerise. Grayson, 1999.
- Mollie Rilstone (s) - Excellent pink picotee sweet pea on a cream ground. Tremewan, 1993.
- Molly Cuer (s) - Pale blue. 1999.
- Monarch (e) - A Spencer Praecox sweet pea.
- Monarch's Diamond (s) - Picotee on cream. Woodcock.
- Monty Don (g) - Small flowered dark maroon sweet pea. Parsons, 1908.
- Moonlight (e) - A deep blue Spencer Praecox variety.
- Moorland Beauty (s) - Rich mauve with large flowers. Albutt, 1995.
- Moorland Mist (s) - Pale lavender. 1998.
- Morning Rose (s) - Pale pink. Kershaw, 1980.
- Morven (s) - Orange-red. Chisholm, 1998.
- Mount Stewart (s) - Mauve, aka Wisley. Harrod.
- Mrs Bernard Jones (s) - Large flowered rose pink sweet pea. B.R.Jones, 1981.
- Mrs C Kay (s) - A very old lavender sweet pea from the 1940s.
- Mrs Chris James (s) - Rose pink.
- Mrs Collier (g) - Cream. Dobbie, 1906.
- Mrs Douglas MacArthur (e) - A salmon Spencer Praecox sweet pea.
- Mrs Jaqui Jones (s) - Navy blue. 2003.
- Mrs Joan Ward (s) - Rose pink. 1996.
- Mrs June Grayson - Magenta. Grayson, 1997.
- Mrs R Chisholm (s) - White. Chisholm, 2009.
- Mrs R Bolton (s) - A very old rose pink sweet pea from the 1940s.
- Mrs Walter Wright (g) - Deep mauve. Eckford, 1903.
- Mumsie (s) - Crimson. 1993.
- Myfanwy Townsend (s) - Scarlet.
- Myrtle Mann (s) - Orange-red. 1993.