| Hostaname | RG | SZ | Leaf color | P | F | Origin |
| H. 'Oakview' David Stone/Peter Ruh 1987 | R | SM | blgr | | | unknown |
| H. 'Obsession' T. Avent 1998 | R | S | gr | | | 'Sparkling Burgundy' sport |
| H. 'Ocean Isle' D. Chopko/R. Solberg 2006 | R | L | blgr,goye | | | 'El Dorado' sport |
| H. 'Odd Ball' H. & D. Benedict 1995 | R | M | blgr | | | 'Northern Mist' hybrid |
| H. 'Ode to Joy' G. Johnson 2004 | R | | | | | 'Moonlight Sonata' sport |
| H. 'Odyssey' B. Arnold 1999 | R | | str,dgr,w | | | ventricosa hybrid |
| H. 'Ogon Hime Tokudama' Japan/Gotemba Nursery/P. Ruh 2002 | R | S | gry | | | unknown |
| H. 'Ogon Sudare' Japan/P. Ruh 2002 | R | | gry | | | unknown |
| H. 'Ogon Tachi' Japan/P. Ruh 2002 | R | L | gry | | | unknown |
| H. 'Ogon Tsushima' Japan/P. Ruh 2002 | R | S | y | | | unknown |
| H. 'Oh by Gosh' T & Z Nursery/ P. Ruh 2000 | R | M | lgr,ye | | | 'Francee' sport |
| H. 'Oh My Heart' Ran Lydell 2001 | R | M | dgr | | | unknown |
| H. 'Oh! Them Golden Slippers' E. Elslager 2002 | R | | goy | | | 'Sea Prize' hybrid |
| H. 'Okazaki' H. Sugita/P. & J. Ruh 2002 | R | | gr | | | kikutii "white back" x gracillima "white back" |
| H. 'Old Black Magic' E. Elslager 1999 | R | | dgr | | | 'Sea Prize' x hypoleuca |
| H. 'Old Cadillac' J. & B. Diesen 1998 | R | | ch>gr>blgr | | | sieboldiana 'Elegans' hybrid |
| H. 'Old Coot' G. Johnson 2004 | R | M | dgr | | | 'Sum and Substance' x yingeri |
| H. 'Old Faithful' William Brincka/Olga Petryszyn 1991 | R | L | gr | R | Y | plantaginea x 'Regal Rhubarb' |
| H. 'Old Glory' H. Hansen/Shady Oaks Nursery 1999 | R | | y,dgre | | | 'Glory' sport |
| H. 'Old Hump Back' V. Wade 1999 | R | | blgr>gr | | | 'Frances Williams' hybrid |
| H. 'Olga's Shiny Leaf' Olga Thiemann/P. & J. Ruh 2004 | R | D | gr | | | 'Lancifolia' sport |
| H. 'Olive Bailey Langdon' Russ O'Harra/Russ O'Harra Hosta Society 1999 | R | L | dgr,ye | | | sieboldiana sport |
| H. 'Olive Oil' J. Dishon 1996 | R | | lgr>go | | | 'Yellow Splash' x hypoleuca |
| H. 'Olympic Edger' Naylor Creek Nursery 1999 | R | S | gr,cre>we | | | 'Gold Edger' sport |
| H. 'Olympic Glacier' Naylor Creek Nursery 2005 | R | | dgr,(w,spgr)e | | | 'Pathfinder' sport |
| H. 'Olympic Gold' Pauline Banyai 1986 | R | M | y>ch | | | unknown |
| H. 'Olympic Sunrise' Naylor Creek Nursery 2005 | R | M | (y>cr),ble | | | 'Katherine Lewis' sport |
| H. 'Omatsu-san Nishiki' Japan/P. Ruh 2002 | R | | ygr | | | unknown |
| H. 'On Golden Pond' E. Elslager 2005 | R | | gr,grye | | | "'Dorothy Benedict' F1" seedling |
| H. 'On Parade' A. Malloy 2003 | R | | crw,gre | PI | | 'Pin Stripe Sister' hybrid |
| H. 'On Stage' Japan/Paul Aden 1986 | R | ML | w,nagre | | | montana sport |
| H. 'On the Border' Doug Beilstein 2007 | R | M | gr,we | | | 'Neat Splash' x 'Blue Wedgwood' |
| H. 'On the Marc' M. Laviana/A. Malloy 1999 | R | S | y>ch,gre | | | 'Ogon Koba' sport |
| H. 'Once upon a Time' J. & S. Wilkins 2002 | R | | blgr,goye | | | "DB-87-1 selfed" x 'Rhapsody in Blue' |
| H. 'One Man's Treasure' H. Benedict/R. Solberg 1999 | R | | dgr | R | | longipes f. hypoglauca seedling |
| H. 'Ooh La La' E. Elslager 2000 | R | | crw,dgre | | | 'Sea Prize' x hypoleuca |
| H. 'Open Hearted' V. Wade 1999 | R | | blgr | | | unknown |
| H. 'Opipara' Maekawa/Schmid/AHS 2002 | R | M | dgr,crye | | | unknown |
| H. 'Ops' A. Malloy 2001 | R | S | lgr,crwe | | | 'Flamboyant' hybrid |
| H. 'Oracle' D. & J. Ward 2003 | R | | gr | | | unknown |
| H. 'Orange Crush' E. Elslager 2000 | R | | goy,crwe | | | 'Sea Prize' x 'Maekawa' |
| H. 'Orange Joy' Kate Carpenter 1979 | R | S | y | | | 'Wogon' x 'Golden Sunburst' |
| H. 'Orange Marmalade' Bob Solberg 2002 | R | | y>w,blgre | | | 'Paul's Glory' sport |
| H. 'Orange Slices' M. Zilis/M. Vanous 2003 | R | | y>cr | | | 'Orange Marmalade' sport |
| H. 'Orinoco Flow' P. Cross 2002 | R | ML | gr | | | 'Glacier Cascade' hybrid |
| H. 'Orion's Belt' D. & J. Ward 2003 | R | | dgr,we | | | 'Pin Stripe' x montana f. macrophylla |
| H. 'Orphan Child' P. Banyai/J. Everson/S. Dapra 2000 | R | | gr | | | unknown |
| H. 'Osprey' Smith/BHHS 1988 | R | SM | blgr | | | Tardiana grex |
| H. 'Otome-no-ka' K. Watanabe/P. Ruh 2002 | R | D | gr | R | Y- | unknown |
| H. 'Ototo San' Japan/Peter Ruh 1990 | R | SM | dgr,nawe | | | unknown |
| H. 'Out of the Blue' Ed Elslager 2003 | R | | str,blgr,y,cr | | | ('Dorothey Benedict' F-1 seedling) hybrid |
| H. 'Outer Limits' P. Bennerup/Alex Malloy 2000 | R | | str,gr,y,cr | | | 'Striptease' sport |
| H. 'Outer Space' Alex Malloy 2003 | R | | gr,we | | | 'Outer Limits' sport |
| H. 'Outhouse Delight' Tony Avent 1998 | R | S | spe,w>gr | | | 'Undulata' hybrid |
| H. 'Outrigger' E. Elslager 2000 | R | | str,gr,cr,y | | | 'Sea Prize' x 'Maekawa' |
| H. 'Over the Rainbow' E. Elslager 2005 | R | L | str | | | (x 'Dorothy Benedict') seedling |
| H. 'Owen Online' R. Snyder 1998 | R | | goy,dgre | | | 'Fortunei Aureomarginata' sport |
| H. 'Oxheart' Eldren W. Minks 1976 | R | M | lgr>dgr | | | 'Green Platter' x nakaiana |
| H. 'Ozark Welcome' C. Helsley 2004 | R | | | | | "'Fascination' sport" sport |