The company was bought out of administration last month and split into Sussex Mushrooms and Thakeham Produce. Sussex covers growing and picking while Thakeham packs and distributes.
Production is 70 tonnes per week and the company has given itself six months to reach 130 tonnes. It is also packing up to 180t a week of Dutch mushrooms.
While Sainsbury's switched to alternative supplies, Asda stood by the company in administration. "We will continue to take product from Sussex Mushrooms to maintain between 25-30% English production in chain," it said.
But Sussex faces an uphill struggle to claw back its former volumes. Asda has started sourcing from Ireland's Monaghan Mushrooms and also buys direct from Sussex's former parent company in the Netherlands.