Flower and bulb growers say uncertainty around any Brexit deal is their "biggest issue" at the moment.
UK and EU officials announced on Sunday that trade deal talks would continue as no agreement had been reached.
PM Boris Johnson warned the sides remained "very far apart" in key areas, but "where there's life there's hope".
Diane Collison, from Collison Cut Flowers in King's Lynn, Norfolk, said whatever the outcome "there will be a lot more that we need to do".
A new deadline for a decision on UK/EU trade talks has not been set - but the ultimate deadline comes on 31 December, when the UK stops following EU trading rules.
Without a trade deal in place by then, the two sides would begin trading on World Trade Organization (WTO) terms, meaning taxes - or tariffs - would be introduced, potentially raising the cost of imported goods such flowers and bulbs.
Mrs Collison said the firm grows 32 million stems of cut flowers and was in the process of setting up a company in the Netherlands to import the bulbs they need to grow their produce.
She said the Dutch company would "be able to deal with the customs and all the documentation that's needed to bring bulbs here in timely fashion and not be held up at the port".
'Winners and losers'
Mrs Collison said Brexit could add "up to 20%" to their costs.
"There's a huge amount of extra paperwork that's going to need to be done - not just if there's no deal, but even if there is a deal," she said.
Her brother-in-law and business partner Ian Collison said: "The biggest issue is the lack of clarity. We still don't know what rules and regulations we are going to have to follow.
"We've had to leave caveats in all our quotes."
Belmont Nurseries, also in King's Lynn, is one of the largest growers of outdoor tulips in the UK, exporting several varieties to the Netherlands.
Mark Eves, director, said: "We want some clear lines on what we have to do as a business.
"If we know what the implications are, we can then deal with them."
But Mr Eves said he was not worried about a no-deal Brexit, saying it meant "we can go back and negotiate, which is better than having a bad deal".
He said "there will be winners and losers" from Brexit.
"It's going to be hard work for six months to a year, but I think things will settle down, we'll get things in place and we'll get on with it," he said.