Graham, who was made redundant this spring, accesses 8,000 varieties of Belgian and Dutch plants from Gimall Plants and Denmark-based ZenFlora. He has 10 customers in the South West, including Lowden Garden Centre in Wiltshire, New Forest Garden Plants in Hampshire and Leekes department stores.
Graham hopes to take the Bath-based business, which has recently joined the HTA, nationwide.
He said: "I want to make accessible the quality growers I used to have access to at Homebase.
"The feedback I was getting was that some garden centres were buying from Dutch lorries, which bought from the auctions, and that could lead to inconsistencies of quality."
He added: "While there is a huge drive within centres to buy British, as we know, not all plants are available from growers over here. This is where Greenhill Plants comes in.
"If centres over here must buy from Europe, let's make it easier to access the best-quality plants from the finest growers."