| Cultivar Name | Plant Size | Origin | Flower Color | Season | Source | Registered |
| 'I'm So Blue' | Large | Unknown | Near-White | June | Schwarz, Jim | .1999 |
| 'I'm So Pretty' | Large | Sport | Pale-Lavender | July | Schwarz, Jim | .2003 |
| 'M Go Blue' | Large | Hybrid | - | July into August | Schmidt, Bevie | .2009 |
| 'Macabe Blue' | Medium | Unknown | Near-White | July | Summers, Alex | --NR-- |
| 'Mad About Blue' | Medium | Hybrid | Pale-Lavender | July | Zilis, Mark | --NR-- |
| 'Maddren' | Giant | Hybrid | Pale-Lavender | June into July | Gilligan, Madelon | .2012 |
| 'Madelynn' | Large | Unknown | Pure-White | June | Darr, D. & Wade, Van | .2007 |
| 'Madison' | Large | Hybrid | Pale-Lavender | June into July | Sanford, Matt | .2011 |
| 'Madison Mine' | Large | Hybrid | Pale-Lavender | July into August | Zilis, Mark & Schwarz, Jim & Schwarz, Karen | .2011 |
| 'Maggie May' | Large | Hybrid | Pale-Lavender | July | Wasitis, Chick | .2001 |
| 'Magic Moment' | Medium | Unknown | - | June into July | Ward, Dr Dick & Ward, Jane | .2015 |
| 'Magic Mountain' | Large | Hybrid | Pale-Lavender | June into July | Ward, Dr Dick & Ward, Jane | .2003 |
| 'Magica' | Large | Hybrid | - | - | Dupre, Dirk | --NR-- |
| 'Magical Mouse Ears' | Miniature | Sport | Light-Purple | July | Fransen, Marco | --NR-- |
| 'Magnificent Michele' | Large | Hybrid | Pale-Lavender | July | Ward, Dr Dick & Ward, Jane | .2005 |
| 'Majestic Blue' | Large | Unknown | - | - | Aden, Paul | --NR-- |
| 'Majordomo' | Large | Unknown | Near-White | August | Deckert, Emile & Deckert, Jane | .2004 |
| 'Mammoth Ears' | Giant | Hybrid | - | June into July | Kruer, George | .2009 |
| 'Mammoth Halo' | Giant | Sport | Near-White | June into July | Aden, Paul | --NR-- |
| 'Mandan' (Wade) | Large | Unknown | - | - | Wade, Van | --NR-- |
| 'Maple Grove' | Giant | Unknown | - | - | Jernigan, Bettie | --NR-- |
| 'Marge' | Medium | Hybrid | Near-White | June into July | Simpers, Lucille & Soules, Marjorie | .1996 |
| 'Margie Weissenberger' | Miniature | Hybrid | Pale-Lavender | June into July | Weissenberger, Henry | .1986 |
| 'Marlu's Marshall' | Large | Hybrid | Near-White | June into July | Overhiser, Martin | .2014 |
| 'Marvelous Millie' | Medium | Unknown | - | June into July | Seaver, Mildred & Walek, Kevin | .2009 |
| 'Mary Chastain' | - | Hybrid | - | - | Goodenough, Rick | --NR-- |
| 'Mary Jo' | Small | Unknown | Pale-Lavender | July | Stone, David & Ruh, Peter | .1987 |
| 'Mary Lou' | Giant | Unknown | Pale-Lavender | July | Banyai, Pauline | .1986 |
| 'Marýke Lokike' | Medium | Hybrid | - | June into July | Lokies, Martin | .2008 |
| 'Master Class' | Giant | Hybrid | Pale-Lavender | June into July | Gilligan, Madelon | .2012 |
| 'Mastodon' | Large | Hybrid | Near-White | June into July | Vaughn, Kevin & Walek, Kevin | .2009 |
| 'Maui Blue Kitten' | Medium | Hybrid | - | - | Vaughn, William | --NR-- |
| 'May' | Small | TC Sport | Pale-Lavender | July | Hansen, Hans | .1999 |
| 'Mayan Seer' | Large | Hybrid | Near-White | June into July | Mitchell, Bill | --NR-- |
| 'McFly' | Medium | Hybrid | - | - | Stadden, Josh | --NR-- |
| 'Mean Joe Green' | Medium | Hybrid | Med-Lavender | July into August | Zolock, Steve & Zolock, Sarah | .2008 |
| 'Melissa' | Medium | Unknown | - | - | Schwarz, Jim | --NR-- |
| 'Memphis Blue' | Giant | Hybrid | - | - | Petryszyn, Olga | .2021 |
| 'Menominee' | Large | Unknown | - | - | Wade, Van | --NR-- |
| 'Merle' | Large | Hybrid | - | - | Wade, Van | .2007 |
| 'Merle's Foundling' | Large | Unknown | Pale-Lavender | July | Simpers, Lucille | --NR-- |
| 'Merri Sherri' | Medium | Unknown | - | - | Vertz, Mary | --NR-- |
| 'Mesa Verde' | Large | Hybrid | Near-White | June into July | Ward, Dr Dick & Ward, Jane | .2004 |
| 'Metallica' | Medium | Hybrid | Med-Lavender | August | Lachman, Wm & Lachman, Eleanor | .1991 |
| 'Metamorphosis' | Large | Hybrid | Light-Purple | July into August | Kwick, Charles | .2017 |
| 'Miami' | Large | Hybrid | Near-White | June into July | Wade, Van | --NR-- |
| 'Michael T. Rozanski' | Giant | Hybrid | Near-White | June into July | Chamberlain, Steve | .2004 |
| 'Michelle' | Large | Unknown | Pale-Lavender | July | Bastille, Jocelyne | --NR-- |
| 'Microchip' | Miniature | Unknown | Light-Purple | July | Benedict, Dr Ralph (Herb) | --NR-- |
| 'Microtardiana' | Medium | Unknown | Med-Lavender | August | Unknown | --NR-- |
| 'Midnight Dream' | Giant | Unknown | - | - | Hackbarth, Robert | .2015 |
| 'Midnight Express' | Large | Hybrid | Pale-Lavender | June into July | Ward, Dr Dick & Ward, Jane | .1996 |
| 'Midnight Hour' | Giant | Unknown | Pale-Lavender | June | Ward, Dr Dick & Ward, Jane | .2009 |
| 'Midwest Blue' | Large | Sport | Near-White | June into July | Summers, Alex | --NR-- |
| 'Mike' | Giant | Unknown | - | June into July | Webster, B. | .2010 |
| 'Mike's Peak' | Large | Unknown | - | - | Summers, Alex | --NR-- |
| 'Milk Road' | Large | Sport | Near-White | June into July | Van den Top, Jan | --NR-- |
| 'Millennium' | Giant | Hybrid | Pale-Lavender | June into July | Wilkins, Dr Jim & Wilkins, Jill | .1995 |
| 'Mill's Master' | Small | Unknown | - | - | Sneyers, Rob | --NR-- |
| 'Mill's Roth-Stone' | Medium | Unknown | - | - | Sneyers, Rob | --NR-- |
| 'Mill's Stilbon' | Small | Unknown | - | - | Sneyers, Rob | --NR-- |
| 'Mimosa Mouse Ears' | Small | Sport | Light-Purple | July | Silvers, Bill | --NR-- |
| 'Ming Dynasty' (Hanson) | Medium | Unknown | - | August | Hanson, Curt | --NR-- |
| 'Ming Jade' | Large | Unknown | Pale-Lavender | July | O'Harra, Russ | .1999 |
| 'Mini Moon' | Miniature | Hybrid | Near-White | - | Lachman, Wm & Lachman, Eleanor | --NR-- |
| 'Minimoon' | Miniature | Hybrid | Near-White | August | Lachman, Wm & Lachman, Eleanor | .1992 |
| 'Minna Blue' | Medium | Unknown | - | August | Ruh, Jean | .1997 |
| 'Minnie Klopping' | Medium | Hybrid | Pale-Lavender | July | Arett, Anne & Klopping, Minnie | .1975 |
| 'Mira' | Giant | Sport | Pale-Lavender | June into July | Maekawa, Dr Fumio & The American Hosta Society | .2002 .2018 |
| 'Mirror Mirror' | Small | Hybrid | - | - | Goodenough, Rick | --NR-- |
| 'Mischief' | Large | Unknown | Near-White | June | Duback, Robyn | .1998 |
| 'Miss Abbie' | Small | Hybrid | Light-Purple | August | Schroeder, Bob & Schroeder, Barb | .2019 |
| 'Miss Linda Smith' | Medium | Unknown | Light-Purple | July | Wrede, Arthur | .2006 |
| 'Miss Lucy' | Giant | Unknown | Near-White | June into July | Simpers, Lucille | --NR-- |
| 'Miss You' | Medium | Hybrid | Pale-Lavender | July | Lockwood, Mikky | .2018 |
| 'Mississippi Delta' | Giant | Hybrid | Pale-Lavender | June into July | Petryszyn, Olga | .1998 |
| 'Mississippi Mist' | Medium | Unknown | - | - | Schulz, Ed | .2014 |
| 'Mississippi Mud' | Giant | Hybrid | Pale-Lavender | July into August | Simmering, Ron | .2000 |
| 'Missouri River' | Small | Hybrid | Near-White | July | Beilstein, Doug & Malloy, Alex | .2005 |
| 'Mister Red Genes' | Large | Hybrid | - | - | Wrede, Arthur | --NR-- |
| 'Misty Waters' | Large | Unknown | Near-White | July into August | Fisher, Eunice V. | .1986 |
| 'Moby Dick' | Large | Hybrid | Near-White | July into August | Brill, Kirk | .1999 |
| 'Mohegan' | Large | Unknown | Near-White | June | Megos, Stan & Malloy, Alex | .1998 |
| 'Mollie's Blaue' | Large | Unknown | - | - | Kohlein, Fritz | --NR-- |
| 'Mommy's Little Monster' | Medium | Hybrid | - | - | Stadden, Josh | --NR-- |
| 'Mona Lisa' | Large | Unknown | Pale-Lavender | June | Ward, Dr Dick & Ward, Jane | .2005 |
| 'Monashee Blue Cup' | Small | Unknown | - | - | Montgomery, John | --NR-- |
| 'Monster Babe' | Giant | Hybrid | Pale-Lavender | - | Minks, Eldren & Malloy, Alex | .2000 |
| 'Montana Blue' | Large | Unknown | - | - | Unknown | --NR-- |
| 'Montel' | Large | Hybrid | - | - | Livingston, Ron | --NR-- |
| 'Montreal Blue Ice Storm' | Giant | Hybrid | Pale-Lavender | June into July | Wade, Van | .2007 |
| 'Mood Indigo' | Large | Hybrid | Pure-White | June into July | Ward, Dr Dick & Ward, Jane | .1996 |
| 'Moody Blues' | Medium | Unknown | Pale-Lavender | - | Oudolf, Piet & Heemskerk, Gerardus | --NR-- |
| 'Moon Is Blue' | Medium | Unknown | - | - | Moldovan, Steve | --NR-- |
| 'Moon Monster' | Large | Unknown | - | June into July | Lachman, Wm & Lachman, Eleanor & Walek, Kevin | .2009 |
| 'Moongate Flying Saucer' | Small | Hybrid | Pale-Lavender | July | Isaacs, Charles & Solberg, Robert | .1996 |
| 'Moonlight Sonata' | Large | Hybrid | Pale-Lavender | August | Johnson, Greg | .2004 |
| 'More Elegant' | Giant | Unknown | Near-White | June | Stadden, Josh | .2001 |
| 'Moscow Blue' | Large | Hybrid | Near-White | July into August | Arett, Anne & The American Hosta Society | .1986 |
| 'Mount Kip' | Giant | Unknown | Light-Purple | July | Simpers, Lucille | --NR-- |
| 'Mountain of Love' | Giant | Unknown | - | - | Ziarek, Ken | --NR-- |
| 'Movin on Up' | Small | Unknown | Med-Lavender | - | Van Wyke, Trudy | --NR-- |
| 'Mr Blue' | Medium | Hybrid | - | July into August | Wrede, Arthur | .2005 |
| 'Mr Red Genes' | Medium | Hybrid | - | - | Wrede, Arthur | --NR-- |
| 'Mr Z' | Medium | Hybrid | Near-White | August to October | Zilis, Mark & Schwarz, Jim & Schwarz, Karen | .2014 |
| 'Mr. Black' | Large | Unknown | - | - | Wrede, Arthur | --NR-- |
| 'Mr. Ed' | Large | Unknown | - | - | Elslager, Ed | --NR-- |
| 'Mrs Mouse Ears' | - | Sport | Light-Purple | July | Unknown | --NR-- |
| 'Mrs. Allen' | Large | Sport | Near-White | June into July | Unknown | --NR-- |
| 'Murasaki Tokudama' | - | Unknown | - | - | Unknown | --NR-- |
| 'Muriel Seaver Brown' | Large | Hybrid | Pale-Lavender | June into July | Seaver, Mildred | .1984 |
| 'Murmurs' | Medium | Unknown | - | - | Minks, Eldren & Malloy, Alex | .2000 |
| 'My Blue Heaven' | Medium | Unknown | Light-Purple | July | Banyai, Pauline & Elslager, Ed | .1997 |
| 'My Friend Bertha' | Small | Sport | Light-Purple | July | Walters Gardens | --NR-- |
| 'My Heart' | Medium | Unknown | Light-Purple | July | Wade, Van | .2007 |
| 'Myles Standish' | - | Unknown | - | - | Unknown | --NR-- |
| 'Mystic Star' | Small | Hybrid | Pale-Lavender | July into August | Johnson, Greg | .2004 |
|