Extension plans were approved for the centre three years ago, following a planning inquiry, but new owner Wyevale Garden Centres, which bought the store last August, wants to increase the size of the additions.
Wyevale representatives have held several pre-planning submission meetings with Sedgemoor District Council, and a revised application is expected to be lodged in coming months.
Currently, the main building covers about 2,600sq m while the outdoor sales area is about 9,500sq m. Planning consent was previously granted to increase the indoor space to about 5,400sq m and the external space to 14,000sq m.
Wyevale plans to extend the internal retail space to 5,800sq m with the external space remaining at 14,000sq m.
Sanders manager Peter Burks said: "It is anticipated that work could start this autumn and be completed next summer."
A new roundabout is proposed to improve traffic flow, while car parking spaces will increase from 369 spaces to 411.