The Bedfordshire centre has won permission through Malcolm Scott Consultants for a restaurant conservatory, carpark surfacing and polytunnel over its compost yard.
Little said: "It's to keep compost dry so can be shopped in the winter. Given the content of growing media has changed somewhat and reading alarming stories about Legionnaires disease linked to compost mainly in Scotland, it felt to me the more we can do to protect customers by storing bags in a dry environment, the better."
Scotland has had 15 cases of Legionella longbeachae since 2008, with some linked to compost. Australia has rules that mean compost bags must carry warnings.
Little said a good year's sales had seen the return of the grow your own and gardener market.
But he said barbecue sales are "now an internet market" with only panic sales still happening in garden centres, who can't compete on price with web sellers.
He said outdoor high level table furniture at £1,000 a suite could be big next season, with Poplars considering stocking Norfolk Leisure, Hartman or Leisuregrow.