| Cultivar Name | Plant Size | Origin | Flower Color | Season | Source | Registered |
| 'Kaiapoi' | Giant | Hybrid | Near-White | June into July | Gilligan, Madelon | .2012 |
| 'Karen Deborah' | Giant | Unknown | Pale-Lavender | June | Simpers, Lucille | --NR-- |
| 'Kasseler Blue' | Medium | Unknown | - | - | Klose, Heinz & Ruh, Peter & Ruh, Jean | .2008 |
| 'Katana' | Medium | Hybrid | - | - | Meyer, Bill | --NR-- |
| 'Kayak' | Large | Unknown | Pale-Lavender | July | Black, Gwen & Ruh, Peter | .1999 |
| 'Keel' | Giant | Hybrid | Near-White | June into August | Gilligan, Madelon | .2012 |
| 'Kelly' | Large | Sport | Near-White | June into July | Scolnik, Patricia & Walek, Kevin | .2009 |
| 'Kempen Magenta Blue' | Large | Hybrid | - | - | Butaye, Patrick | --NR-- |
| 'Kempen Sky High' | Medium | Hybrid | Light-Purple | July into August | Butaye, Patrick | .2015 |
| 'Kenn's Little Blue Lightning' | - | Unknown | - | - | Unknown | --NR-- |
| 'Kenny Love Blue' | Large | Unknown | - | June into July | Wade, Van & Walek, Kevin | .2009 |
| 'Kerry Man' | Giant | Sport | Near-White | June into July | Gilligan, Madelon | .2015 |
| 'Kim' | Giant | Hybrid | - | June into July | Kwick, Charles | .2016 |
| 'Kimmie Q' | Giant | Hybrid | Near-White | June into July | Kwick, Charles | .2017 |
| 'Kind of Blue' | Large | Unknown | - | July | Ward, Dr Dick & Ward, Jane | .1999 |
| 'King David' | Medium | Hybrid | Near-White | July into August | Zolock, Steve & Zolock, Sarah | .2001 |
| 'King John' | Giant | Sport | - | July into August | Schwarz, Jim | .2010 |
| 'Kingfisher' | Medium | Unknown | Pale-Lavender | August to October | Smith, Eric & British Hosta and Hemerocallis Society | .1988 |
| 'King's Avenger' | Large | Unknown | - | - | King, Herb | --NR-- |
| 'King's Bishop' | Large | Unknown | - | - | King, Herb | --NR-- |
| 'King's Brute' | Medium | Unknown | - | - | King, Herb | --NR-- |
| 'King's Charmer' | Large | Unknown | - | - | King, Herb | --NR-- |
| 'King's Counsel' | Large | Unknown | - | - | King, Herb | --NR-- |
| 'King's Dominion' | Large | Unknown | - | - | King, Herb | --NR-- |
| 'King's Grandeur' | Large | Unknown | - | - | King, Herb | --NR-- |
| 'King's Hidden Treasure' | Large | Unknown | - | - | King, Herb | --NR-- |
| 'King's Highcliff Castle' | Medium | Unknown | - | - | King, Herb | --NR-- |
| 'King's Loyalty' | Large | Unknown | - | - | King, Herb | --NR-- |
| 'King's Magician' | Large | Unknown | - | - | King, Herb | --NR-- |
| 'King's Majestic Blue' | Large | Unknown | - | - | King, Herb | --NR-- |
| 'King's Pendragon' | Large | Unknown | - | - | King, Herb | --NR-- |
| 'King's Redemption' | Medium | Unknown | - | - | King, Herb | --NR-- |
| 'King's Sir Percival' | Medium | Unknown | Near-White | - | King, Herb & King, Gladys | --NR-- |
| 'King's Sir Rupert' | Large | Unknown | - | - | King, Herb | --NR-- |
| 'King's Warrior' | Large | Unknown | - | - | King, Herb | --NR-- |
| 'Kirkside Blue' | Large | Hybrid | Pure-White | July | Hanna, Clarence | .2018 |
| 'Kite' | Medium | Unknown | - | - | Smith, Eric & British Hosta and Hemerocallis Society | .1988 |
| 'Kiwi Antarctica' | Small | Hybrid | Near-White | - | Sligh, Barry | --NR-- |
| 'Kiwi Biddy Blue' | Small | Hybrid | - | - | Sligh, Barry | --NR-- |
| 'Kiwi Blue Baby' | Small | Hybrid | Pale-Lavender | July | Sligh, Barry | .1999 |
| 'Kiwi Blue Canoe' | Small | Unknown | - | - | Sligh, Barry | --NR-- |
| 'Kiwi Blue Heron' | Large | TC Sport | Near-White | June into July | Sligh, Barry | --NR-- |
| 'Kiwi Blue Magic' | Large | Unknown | - | - | Sligh, Barry | --NR-- |
| 'Kiwi Blue Ruffles' | Large | Hybrid | Near-White | June | Sligh, Barry | .1999 |
| 'Kiwi Blue Sky' | Small | Hybrid | Pure-White | June into July | Sligh, Barry | .1999 |
| 'Kiwi Blue Waves' | - | Unknown | - | - | Sligh, Barry | --NR-- |
| 'Kiwi Canoe' | Medium | Hybrid | Pure-White | June into July | Sligh, Barry | .1999 |
| 'Kiwi Jordan' | Small | Unknown | Light-Purple | August | Sligh, Barry | .2000 |
| 'Kiwi Midnight' | Giant | Unknown | - | - | Sligh, Barry | --NR-- |
| 'Kiwi Milky Way' | Large | Sport | Near-White | June into July | Sligh, Barry | .2000 |
| 'Kiwi Minnie Blue' | Miniature | Hybrid | Med-Lavender | July into August | Sligh, Barry | .1999 |
| 'Kiwi Pacific Blue' | Medium | Hybrid | Pale-Lavender | June | Sligh, Barry | .1999 |
| 'Kiwi Red Heron' | Large | Unknown | - | - | Sligh, Barry | --NR-- |
| 'Kiwi Ruffles' | Large | Unknown | - | - | Sligh, Barry | --NR-- |
| 'Kiwi Skyscraper' | Large | Hybrid | Pale-Lavender | July into August | Sligh, Barry | --NR-- |
| 'Kiwi Summer Haze' | Small | Unknown | Pale-Lavender | July into August | Sligh, Barry | --NR-- |
| 'Kiwi Waves' | Large | Hybrid | Pale-Lavender | July | Sligh, Barry | .1999 |
| 'Ko Urajiro' | - | Unknown | - | - | Unknown | --NR-- |
| 'Krinkled Cup' | Medium | Unknown | - | - | Wade, Van | --NR-- |
| 'Krinkled Joy' | Large | Hybrid | Near-White | June into July | Arett, Anne & Armstrong, Maxine & The American Hosta Society | .1986 |
| 'Kris Krinkle' | Large | Hybrid | Med-Lavender | June into July | Postlewaite, Peter | .2013 |
| 'Krossa Regal' | Giant | Hybrid | Pale-Lavender | July into August | Krossa, Gus & Summers, Alex | .1980 |
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