The monthly glossy title, priced at £2.90, will target "lifestyle gardeners".
It will be available from 26 May to coincide with the Chelsea Flower Show. And it will be backed by a marketing campaign, by Big Al, which will include both national and regional press advertising using the line: "A breath of fresh air for your garden." Below-the-line activity, to be developed in-house, is also planned.
Seven sees Gardenlife's target audience as 35- to 44-year-old AB males and females. It regards this as an untapped market in the sector.
Paula McWaters, the former gardening editor of the BBC's Good Housekeeping, is the editor of the title.
The launch follows that of the food magazine Delicious, the publisher's first title, which made its debut at the end of last year. Gardenlife is the first title to launch since Guardian Media Group took a stake in Seven last month.
Gardenlife lines up against the BBC's market-leading Gardeners' World, Emap's Garden Answers and IPC's Amateur Gardening.