Environment Agency invasive species technical adviser Trevor Renals said last week that he holds his head in his hands when he walks around garden centres.
A Defra representative said: "We are currently considering proposals to ban the sale of some highly invasive non-native plants, but gardeners also need to take steps to prevent them from taking hold and spreading in the first place.
"We will continue to work closely with the horticulture and conservation sectors to promote responsible use of aquatic plants through the Be Plant Wise campaign."
Defra said many retailers were already taking steps to ensure that customers know what they are buying and advising them on how to dispose of unwanted pond waste properly.
An Environment Agency spokesman said Defra controls what plants are sold in garden centres: "It's not within our powers to limit sales. The most we can do is clean up waterways of plants such as Ludwigia and Japanese knotweed if they are having an impact on Water Framework Directive targets. People should report issues to the Non-native Species Secretariat."