Its statement comes in response to reports that government funding was withheld from a green infrastructure project planned by Coventry City Council because the air-purifying role of the trees was unproven.
Defra said it did not advise that trees are ineffective against air pollution, but that other measures can have a quicker impact.
A Defra representative told Horticulture Week: "Early last year local authorities were able to enter submissions for early access to funding intended to improve air quality. The measures proposed were expected to be implemented very quickly and have a significant impact on air quality."
Coventry’s submission initially included a green infrastructure scheme, though without trees, but this was dropped as the council did not provide evidence that this would have a significant impact on air quality, he explained.
"However other elements of their bid did meet the criteria, resulting in them being awarded more than £2m," he said. "We do not discourage the planting of trees or development of new green spaces by local authorities, but these air quality plans are intended to provide significant improvements to air quality in the shortest possible time."
Explaining the government's position on trees and air quality more generally, he said: "While there is evidence that healthy, well-chosen and well placed urban trees can provide a large range of benefits valuable to the economy and to people, including a relatively small impact on urban air quality, current evidence suggests that trees would not be enough to solve the air quality problems at a city scale."