"It's no good thinking about it on 1 March, which some garden centres have been guilty of, jumping on board late. We published the dates a year ago."
The event has raised £120,000 for Greenfingers since 2012. Organisers want a full list of participants in time for the Garden Press Event on 13 February.
Celebrities including David Tennant, Jude Law, Danny Dyer and Naomie Harris have voiced garden quiz questions for garden centres to use in events.
Cultivation Street and the Royal British Legion poppy seed appeal will launch at the same time. Easter weekend falls a fortnight later this year, on 18-20 April, and Douglas-Davies said: "We need to make sure that the season starts early. No-one wants a late season."
Scotsdales managing director Caroline Owen said she wants the centre to be ready for 3 February, when promotional magazine Beautiful Gardens is distributed.
Douglas-Davies, who is set to add to his two-centre Hillview Group, said he expects to have Christmas fully out by 18 January.