| Cultivar Name | Plant Size | Leaf Color | Variegation | Var Color | Origin | Flower Color | Season | Source | Registered |
| 'Oh Henry' | Medium | Blue/Green | Streaked | Yellow | Unknown | - | - | Unknown | --NR-- |
| 'OHS Butter Pat' | Medium | - | - | - | Hybrid | - | - | Ontario Hosta Society | --NR-- |
| 'OHS Calamari' | Small | Med-Green | Medial | White | TC Sport | Light-Purple | August to September | Lasek, Robert & Ontario Hosta Society | .2008 |
| 'Olive Oil' | Medium | Yellow | - | - | Hybrid | Pale-Lavender | - | Dishon, Jim | .1996 |
| 'Omlett' | Large | Yellow | - | - | Hybrid | - | - | Kohlein, Fritz | --NR-- |
| 'One-trip Salad Bar' | Small | Dark-Green | Marginal | Yellow | Nat-Sport | Med-Lavender | July into August | Solberg, Robert | --NR-- |
| 'Orange Crush' | Medium | Med-Green | Marginal | Creamy White | Hybrid | Pale-Lavender | July | Elslager, Ed | .2000 |
| 'Orange Ice' | - | Yellow | - | - | Unknown | - | - | Hawes, James | --NR-- |
| 'Orange Joy' | Small | Yellow | - | - | Hybrid | Light-Purple | July | Carpenter, Kate | .1979 |
| 'Orange Marmalade' | Large | Med-Green | Medial | White | Sport | Pale-Lavender | July into August | Solberg, Robert | .2002 |
| 'Orange Slices' | Medium | Yellow | - | - | TC Sport | Pale-Lavender | July into August | Zilis, Mark | .2003 |
| 'Oreo Cookies' | - | - | - | - | Duplicate | - | - | Duplicate Name | --NR-- |
| 'Oreo Cream' | Medium | Dark-Green | Medial | White | Sport | Pale-Lavender | July into August | Ziarek, Ken | --NR-- |
| 'Osiris Pacha' | Medium | Med-Green | Marginal | Yellow | Unknown | - | - | Fafard, Serge | --NR-- |
| 'Oyster Bay' | Medium | Blue/Green | Marginal | Yellow | Nat-Sport | Med-Lavender | August | Solberg, Robert | --NR-- |
| 'Oyster Crackers' | Medium | - | - | - | Unknown | - | - | Ziarek, Ken | --NR-- |
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