Unpublished research conducted on the HTA's behalf by the Future Foundation Vision programme found 35 per cent agreed with the statement "I like to try lots of different leisure activities rather than concentrate on a few", against 43 per cent in a previous survey.
HTA marketing director Andrew Maxted said: "Five years ago, people were busy and doing as many leisure activities as they could.
"Now people want more quality time and gardening is one of the great beneficiaries of that."
Maxted added that there was a "huge pent-up demand" for gardening and garden products that even bad weather would not slow down.
The HTA strategy will be revealed at its council meeting in May.