Hortus Loci co-founder Mark Straver has complained that banks are making it almost impossible for UK nurseries to supply the home market.
Straver, who set up the Hampshire nursery in 2011, said getting funding is a "nightmare" that he "never wants to go through again".
He added: "Borrowing money to buy this nursery was horrific. We turned over £1.5m in the first year and the business was going somewhere, but we had no bank safety net and without our investors we would have been buggered.
"It boils down to who is in the bank you can find who supports your idea. It doesn't matter which bank." Straver praised the support of NatWest senior relationship manager Julie Larrard, who backed his business.
He said most of the trees designers will use at the RHS Chelsea Flower Show will come from overseas because banks make nurseries difficult to set up, while land and labour is too costly.
"In Germany, Holland or Belgium, banks will lend you money to pay back when you retire. In England, you might as well be dealing with a drug dealer or loan shark.
"The average business bank loan in the UK is 10 years, but the Europeans' mentality to banking and finance is for a lifetime. It would be nice to get stuff over here but there is no cheap land or labour any more near your customers."
Continental nurseries such as Lappen, Bruns and von Ehren "are all 150 years old and family-owned", he pointed out.
Straver dismissed issues about tree diseases such as ash dieback coming in on continental stock. "It's easy to blame importers but nurseries have been importing for many years. We liaise with Defra all the time and have everything checked by Defra."
He spends two days a week from September to April sourcing stock in Europe. "I source the best stock. Delivery logistics from Europe tend to be better. If I want it in three days from Belgium, it would happen, but not necessarily from England."
Straver said at least half of the trees at Chelsea are from the continent, though he added that all the perennials are English-grown.
Chelsea show gardens - Major supplier
Hortus Loci is the biggest single plant supplier for Chelsea show gardens this year and is being used by Jinny Blom, Chris Beardshaw, Nigel Dunnett and Robert Myers.
It has also sourced plants for Straver's former employer Crocus, which is supplying Ulf Nordjfell at Chelsea.
In 2012, Straver had to work one day each week for Crocus - which is also supplying Christopher Bradley-Hole at Chelsea this year - as part of his leaving deal.
The nursery's Whitewater retail nursery opened at Easter, with "50p whips to £5,000 trees and everything in between".