Speaker JZ Flowers commercial manager Joanne Plant said only Tesco was truly static with 33.2 per cent of the market in value and volume.
However, some retailers such as the Co-operative group have seen increases in market share this year.
Dutch production has declined in recent years while the equatorial belt - Kenya, Ethiopia and Ecuador/Columbia - has increased, she said.
"The market is static overall but that's because there are clear winners and losers," she said.
She added that indoor plants were growing, with a 7.2 per cent increase in value and 1.2 per cent in volume:
"Indoor plants are what's driving the market," she said.
HTA market information manager David Denny added that plant sales have hovered around £1.6-1.7 billion since the collapse of Lehman Brothers in 2007.
"Plants are not recession proof but are relatively resistant to the economic pressures we've seen," he said.