Although roses were grown inside greenhouses, no amount of artificial heat could compensate for the absence of sunshine.
"We would have had more roses to sell if they had come on earlier. The colder weather has delayed them by up to two weeks."
Cutting stems started last week, to be bunched and chilled before being sent to the flower market.
Because they were grown locally and delivered while still fresh, they should last up to two weeks, Mr van Delft said.
The main grower south of Christchurch, he said the market was increasingly being supplied by roses from India.
Flower Growers Association chairman David Blewden said only about half the 600,000 rose stems bought nationwide for Valentine's Day were grown in New Zealand, with the rest imported from India.
"Import volumes are growing each year because stems are mass-produced overseas very cheaply, putting our local industry under severe pressure. Unfortunately, consumers don't know that most of the roses they buy are imports," he said.
About 12 million rose stems are grown commercially in New Zealand each year, with about 3 million imported.