| Company |
| O.A. Taylor and Sons Bulbs Ltd (Taylors Bulbs) |
| O'Bannon Springs Daylilies |
| O’Brien Nurserymen, LLC |
| Oak Hill Daylilies |
| Oak Hill Farm |
| Oak Hill Farm Nursery |
| Oak Hill Gardens |
| Oak Knob Orchids |
| Oak Meadow Farm Daylilies and Hostas |
| Oak Prairie Farm |
| Oak Tree Seed |
| Oakcrest Perennial Gardens & Nursery |
| Oakes Daylilies |
| Oakhill Garden |
| Oakland Nurseries |
| Oakleigh Nurseries |
| Oakridge Nursery |
| Oakwood Daffodils (Dr. John Reed) |
| Oasis Exotics |
| Oasis Products Inc. |
| Obsession Orchids |
| Oceangrown (Ocean Grown) |
| OdlaNu i Sverige AB |
| Odom's Orchids, Inc. |
| Odyssey Bulbs |
| Odyssey Perennials |
| Oesco, Inc. |
| Of the Earth Native Plant Nursery |
| OFE International |
| Ogden Station Daylilies |
| Oh My Peonies |
| Ohio Earth Food Inc. |
| Ohio Heirloom Seeds |
| Ohio Prairie Nursery |
| Ohio Seeds (Ohioseeds.com) |
| OIKOS Tree Crops |
| Okami Gardens Bonsai |
| Oklahoma GARDENER |
| Olallie Daylily Gardens |
| Old Brook Gardens |
| Old Court Nurseries (AutumnAsters.com) |
| Old Field Garden & Wild Flower Nursery |
| Old Hendrik |
| Old House Gardens - Heirloom Bulbs |
| Old Man Cactus |
| Old Pueblo Plant & Seed Company |
| Old Stage Farm |
| Old Sturbridge Village Seeds |
| Old World Gazebos |
| Old_Tyme_Country_Nursery |
| Olde English Garden Shoppe |
| Oleo Acres |
| Olive Barn |
| Olive Road Nursery |
| Olive Tree Growers |
| Olympia Orchids |
| Olympic Orchids |
| oMioBio - Peter Müller |
| Ommas-Aarden |
| Omni Farm |
| On the Garden Line® Newsletter |
| Onalee's Seeds, LLC |
| One Gallon Plants |
| One Green World |
| One Stop Poppy Shoppe |
| OneDollarSeedStore.com |
| Ono Essence |
| Ontario Orchids, Inc. |
| Ontario Seed Company, Ltd. (OSC) |
| Oopsa Daisy,LLC. |
| Opus Plants |
| Orange Pippin |
| Orchard House Heirlooms |
| Orchard Nurseries |
| Orchard Valley Supply Inc. |
| Orchard's Edge |
| Orchid Answers |
| Orchid Containers Inc. |
| Orchid Gardens |
| Orchid Images |
| Orchid Island Orchids |
| Orchid Select |
| Orchid Style |
| Orchidaceae |
| Orchidarium Inc. |
| Orchidbabies, LLC |
| OrchidLight.com |
| Orchidpeople LLC |
| Orchids 'R' Us (Camp Lot A Noise Tropicals) |
| Orchids & More |
| Orchids by Hausermann |
| Orchids by Ohlman |
| Orchids By Post |
| Orchids For The People |
| Orchids in our Tropics |
| Orchids Limited |
| Orchids of Hawaii |
| Orchids of Los Osos |
| Orchids of Olinda |
| Orchids of Wickford |
| Orchids Royale |
| Orchids.com (Norman's Orchids) |
| OrchidSupplies.com |
| OrchidView |
| Oregon Grown Nurseries LLC |
| Oregon Miniature Roses |
| Oregon Small Trees |
| Oregon, Planet Earth (Earthmarks™ Garden Markers) |
| Organic Bountea (formerly Alaska Bountea) |
| Organic Carolinas, LLC |
| Organic Composter |
| Organic Digester |
| Organic Garden Grower |
| Organic Gardening |
| Organic Growers Supply |
| Organic Heirloom Gardens |
| Organic Humus Products |
| Organic Nutrients Insect Frass (onfrass.com) |
| Organic Power Products |
| Organic Seed People |
| Organic Worm Composting (Hoykim Industries) |
| Organica Seed |
| OrganicGardening.com |
| Organics Today |
| OrganicSeeds.co.uk |
| Orgel's Orchids |
| Oriental Garden Supply |
| Oriental Orchids |
| Original Touch Unusual Garden Seeds |
| Orion Farm |
| Orion Industries |
| Orlando Bonsai |
| Ornamental Edibles |
| Ortanique |
| Osborne Seed Company, LLC |
| OtherFellow Plants |
| Ottis Houston's Countryside Daylilies |
| Otway Herbs |
| Ouachita Mountain Blueberry Nursery |
| Oudean's Willow Creek Nursery |
| Our Kids' Orchids & Nursery |
| Out of Africa |
| Outbackpatio |
| Outdoor Distributors |
| Outdoor Expressions |
| Outdoor Furniture Online |
| Outdoor Patio Furniture |
| Outdoor Statues Shop (OutdoorStatuesShop.com) |
| Outdoor Wood Furniture Inc. |
| Outdoorrrama! TwinComposter doors |
| Outdoors by Design, LLC (formerly Halfside Bamboo Nursery and Display Garden) |
| Outsidepride.com |
| Outstanding Seed Company LLC |
| Overhill Gardens |
| OVM Seeds |
| Owen Farms |
| Owens Orchids, LLC |
| Owl's Head Garden Products |
| Oxbow Farms |
| OxBow Wreaths |
| Oyster Cove Plant & Flower Seeds |
| Ozark Mountain Apparel |
| Ozark Perennials |
| Ozark Plant Co |
