DLKW won the business, which is worth £2 million, following a three-way pitch against the incumbent, BMP DDB, and the branding and communications business Sandom Group.
The agency had held the account before it moved to BMP three years ago and unveiled the debut television commercial for the Scotts UK-owned brand in 2000.
Scotts' pan-European business was subsequently united under BMP in a reshuffle. The other leading Scotts brands, which include Weedol and Miracle-Gro, will continue to be handled by BMP.
The agency is understood to be planning a TV-based campaign for Evergreen, which is scheduled to break at the beginning of next year.
Alex Kuropatwa, the business development director at DLKW, said: "There's something very satisfying about winning back a piece of business that has strayed. We won it with a very impactful, big idea that will stir things up come launch next year."
DLKW injected an element of humour into its initial campaign for the gardening product. The campaign, which demonstrated how easy it is to use Evergreen Grasshopper, targeted people who enjoy their garden but don't regard themselves as experts.
Evergreen is DLKW's eighth new-business win of 2003. The agency's most recent wins were Batchelors and Vauxhall Astra.