| Cultivar Name | Plant Size | Leaf Color | Variegation | Var Color | Origin | Flower Color | Season | Source | Registered |
| 'Odina' | Large | Blue/Green | - | - | Unknown | - | - | Wade, Van | --NR-- |
| 'Ogon Otome Hideko' | Miniature | Yellow | - | - | Unknown | - | - | Unknown | --NR-- |
| 'Oh Audrey' | Medium | Light-Green | Marginal | White | Sport | Pure-White | June into July | Silvers, Bill | .2013 |
| 'Oh Charlie' | Large | Med-Green | Marginal | Yellow | TC Sport | Pale-Lavender | July | Ziarek, Ken | --NR-- |
| 'Oh Cindy' | Medium | Light-Green | - | - | Sport | Pale-Lavender | July | Benedict, Dr Ralph (Herb) | --NR-- |
| 'Oh Dannyboy' | Large | Dark-Green | - | - | Unknown | - | - | Skaggs, Virginia & Skaggs, Brian | --NR-- |
| 'Oh Henry' | Medium | Blue/Green | Streaked | Yellow | Unknown | - | - | Unknown | --NR-- |
| 'Oh! Susanna' | Medium | Blue/Green | - | - | Hybrid | Med-Lavender | June into July | Reuter, Laurence & Gilligan, Madelon | .2015 |
| 'Ohh! Blue Otto' | Small | Blue/Green | - | - | Unknown | - | - | Schulz, Ed | .2009 |
| 'Ohh! Charlotte!' | Large | Yellow | - | - | Unknown | - | June into July | Schulz, Ed | .2012 |
| 'Ohh! Clare' | Large | Yellow | - | - | Unknown | - | July into August | Schulz, Ed | .2016 |
| 'Ohh! Elvira' | Large | Yellow | - | - | Unknown | - | July into August | Schulz, Ed | .2016 |
| 'Ohh! Jewell' | Large | Yellow | - | - | Unknown | Near-White | June into July | Schulz, Ed | .2017 |
| 'Ohh! Laurel' | - | Yellow | - | - | Unknown | - | - | Schulz, Ed | .2009 |
| 'Ohh! Viola' | Medium | Yellow | - | - | Unknown | Near-White | June into July | Schulz, Ed | .2015 |
| 'OHS Bryan's Blue' | Medium | Blue/Green | - | - | Hybrid | - | - | Ontario Hosta Society | --NR-- |
| 'OHS Butter Pat' | Medium | - | - | - | Hybrid | - | - | Ontario Hosta Society | --NR-- |
| 'OHS Margot's Delight' | Medium | Blue/Green | - | - | Sport | Pale-Lavender | July into August | Ontario Hosta Society | --NR-- |
| 'Olga' | - | - | - | - | Unknown | - | - | Unknown | --NR-- |
| 'Olga's Shiny Leaf' | Small | Dark-Green | - | - | Sport | Med-Lavender | - | Thiemann, Olga & Ruh, Peter & Ruh, Jean | .2004 |
| 'Oliver' | Small | Med-Green | Marginal | White | Unknown | - | - | O'Harra, Russ | --NR-- |
| 'Oliver Garden' | Medium | Med-Green | Streaked | White | Unknown | - | - | Unknown | --NR-- |
| 'Olive's Freckles' | Giant | Med-Green | - | - | Unknown | Pale-Lavender | July | Pauley, Olive | --NR-- |
| 'Olivia' | Medium | Blue/Green | - | - | Unknown | Near-White | - | Schwarz, Jim | --NR-- |
| 'Omar the Tentmaker' | Large | Med-Green | - | - | Unknown | - | - | Unknown | --NR-- |
| 'Oriana' | Medium | Yellow | - | - | Sport | Pale-Lavender | July into August | Smith, Eric | --NR-- |
| 'Orphan Annie' | Miniature | Med-Green | Marginal | White | Unknown | Light-Purple | July | Unknown | --NR-- |
| 'Our Friend Reldon' | Large | Blue/Green | - | - | Hybrid | - | - | Van Wyke, Trudy | --NR-- |
| 'Owen Online' | Large | Dark-Green | Medial | Yellow | Sport | Med-Lavender | July | Snyder, Ron | .1998 |
| 'Owens Outrage' | Medium | Light-Green | - | - | Unknown | Med-Lavender | - | Moore, Jeff | --NR-- |
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