The 17 retail units alongside Van Hage are mostly let, with HobbyCraft, clothing suppliers Cotswold and Cotton Traders, Pets Corner, Maidenhead Aquatics and cookware company Le Creuset among the takers.
Five more names are set to be announced soon, with a cafe proprietor among them.
Garden Park Investments chief executive Edward Olley said the park was originally due to open in late 2009 but could not run the risk of any delay before Christmas opening.
He said: "We're targeting the parent/child market. This is a meeting spot with a more pleasant environment to go to than a retail park with a DIY store."
The site also has a "woodland walk" for schools, a range of cafes and events areas at the front for performers.
Units start at not much more than 100sq m, unlike at conventional retail parks. Peterborough has similarities to the £17m-turnover Wyevale-anchored site at Bicester Avenue opened in 2007. Olley said: "This is similar to Bicester but is a more open site. We learnt from Bicester about the level of detail design-wise."
Olley said the garden centre is "obviously" the core of the site and turnover is potentially the same as at Van Hage Great Amwell - around £10m. Van Hage has agreed a 25-year lease on the 4,645sq m garden centre property and the 7,432sq m external sales area.
HPW is ready to fit out the centre in time for opening in February, with an official opening in March 2010.
Cushman & Wakefield and Hammond Phillips are joint letting agents for the scheme.