The 1.4ha site is now owned by the Dilley family, and employs 40 people but is looking to recruit a further 20 staff.
Playdell Smithyman is working on a redevelopment including an enlarged 180-seat café, with a new kitchen and on-site bakery.
There will also be a pets and aquatics centre and expanded gift and homeware selection.
The main building and café will be ready for Christmas and the garden and plant area for Easter 2017. The pets and aquatics centre will follow shortly after.
Marlows will remain open throughout the redevelopment.
#Meanwhile, windows and conservatories company SEH BAC has opened a show centre at Bypass Nurseries near Ipswich.