Groves Nurseries in Bridport officially opened Little Groves Nursery 11km away last week. It has a shop, small demo area and space for around 2,000 plants.
Landscape-design company Marshall James Garden Development (MJGD) is letting the site.
New centre manager Becky Groves - daughter of chief executive Clive Groves - said: "Marshall James ran a small nursery on the site but could only do this half-heartedly as its main focus was on landscape design. We looked at the site and liked its feel. It takes the pressure off our existing base, which has national collections of parma and sweet violets, and gives us another specialism."
She said the nursery would retain its traditional, old-fashioned feel, growing plants to sell on-site and supplying its sister site in Bridport.
The nursery stands among show gardens designed and maintained by Chelsea gold-winner MJGD.