The app's founders aim to replace the catalogue model offering sellers a place to sell plants that can be sent direct to customers.
GardenTags co-founder Daniel Richards describes the app, which recently won investment from technology provider C5 Alliance, was "an Ebay for gardeners".
The two-year-old site has 1.5m comments, 400,000 plant photos shared and 100,000 registered users, with 20% in the US.
There is no hosting fee but the site charges a commission. Richards said: "We’d love to be the UK’s largest marketplace for garden lovers."
Richards said he plans to approach smaller independent nurseries.
Hillier and Plantagogo are among members.
Dobbies is also looking at providing a new route to market for smaller nurseries by offering them a web platform to drive sales through Dobbies' garden centres.