| Cultivar | Reference | Plant Size | Leaf Color | Variegation | Var Color | Origin | Flower Color | Season | Source | Registered |
| 'Oasis' (Ward) | - Rock Band | Large | Blue/Green | - | - | Unknown | Near-White | June into July | Ward, Dr Dick & Ward, Jane | .2012 |
| 'Oberland Colourful Noise' | - Purist | Large | Dark-Green | Streaked | White | Sport | Med-Lavender | July into August | Rank, Stefan | .2013 |
| 'Obsession' | - Animotion | Medium | Med-Green | Marginal | Greenish White | Sport | Light-Purple | August | Avent, Tony | .1998 |
| 'Ode To Joy' | - Ludwig van Beethoven & Friedrich Schiller | Small | Med-Green | - | - | Sport | Near-White | July | Johnson, Greg | .2004 |
| 'Oh Baby Mine' | - The Statler Brothers | Miniature | Dark-Green | - | - | Unknown | - | - | Unknown | --NR-- |
| 'Oh Cindy' | - The Beach Boys | Medium | Light-Green | - | - | Sport | Pale-Lavender | July | Benedict, Dr Ralph (Herb) | --NR-- |
| 'Oh Dannyboy' | - Folk Song | Large | Dark-Green | - | - | Unknown | - | - | Skaggs, Virginia & Skaggs, Brian | --NR-- |
| 'Oh Henry' | - Millie Small | Medium | Blue/Green | Streaked | Yellow | Unknown | - | - | Unknown | --NR-- |
| 'Oh My Darling' | - Folk Song | Small | Light-Green | - | - | Unknown | - | - | Unknown | --NR-- |
| 'Oh My Heart' | - R.E.M. | Medium | Med-Green | - | - | Unknown | Light-Purple | July | Lydell, Ransom | .2001 |
| 'Oh! Susanna' | - Stephen Foster | Medium | Blue/Green | - | - | Hybrid | Med-Lavender | June into July | Reuter, Laurence & Gilligan, Madelon | .2015 |
| 'Oh! Them Golden Slippers' | - Folk Song | Large | Yellow | - | - | Hybrid | Light-Purple | July | Elslager, Ed | .2002 |
| 'Old Black Magic' | - Frank Sinatra | Medium | Dark-Green | - | - | Hybrid | Pale-Lavender | July | Elslager, Ed | .1999 |
| 'Old Blue Eyes' | - Frank Sinatra | Medium | Blue/Green | | | Unknown | Pale-Lavender | July | Goodwin, Randy | .2021 |
| 'Old Faithful' | - Eddy Arnold | Large | Med-Green | - | - | Hybrid | Pure-White | August to October | Brincka, Wm & Petryszyn, 0lga | .1991 |
| 'On the Border' | - Al Stewart, The Eagles | Medium | Med-Green | Marginal | White | Hybrid | Pale-Lavender | August | Beilstein, Doug | .2007 |
| 'Once upon a Time' | - Frank Sinatra | Medium | Med-Green | Marginal | White | Hybrid | Near-White | August | Wilkins, Dr Jim & Wilkins, Sandy | .2002 |
| 'One and Only' | - Adele | Large | Yellow | - | - | Hybrid | Pale-Lavender | June into July | Ward, Dr Dick & Ward, Jane | .2015 |
| 'One Fine Day' | - The Chiffons | Medium | Med-Green | Marginal | Yellow | Hybrid | Near-White | June into July | Ward, Dr Dick & Ward, Jane | .2012 |
| 'One Last Dance' | - Silverstein | Large | Dark-Green | Marginal | Yellow | TC Sport | Near-White | July | Hansen, Hans & Walters Gardens | --NR-- |
| 'Only You' | - The Platters | Medium | Med-Green | Marginal | White | Hybrid | - | - | Ward, Dr Dick & Ward, Jane | .2012 |
| 'Ooh La La' | - Faces | Medium | Blue/Green | Medial | Yellow | Hybrid | Light-Purple | July | Elslager, Ed | .2000 |
| 'Orinoco Flow' | - Enya | Medium | Med-Green | - | - | Hybrid | Pale-Lavender | July into August | Cross, Peter | .2002 |
| 'Orphan Annie' | - Musical Theater | Miniature | Med-Green | Marginal | White | Unknown | Light-Purple | July | Unknown | --NR-- |
| 'Over the Rainbow' | - Judy Garland | Large | Med-Green | Streaked | Speckles | Hybrid | Near-White | June into July | Elslager, Ed | .2005 |
| 'Oyo Como Va' | - Santana | Medium | Med-Green | - | - | Unknown | - | - | Bastille, Jocelyne | --NR-- |
| 'Ozzfest' | - Ozzie Osborne | Medium | Med-Green | Streaked | White | Sport | Near-White | July | Zilis, Mark | --NR-- |
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