The scheme has expanded since its launch in 2008, when 15,500 schools signed up.
Among other rewards, they collected 43,000 pairs of gardening gloves and 12,500 watering cans.
Morrisons gives out a voucher each time shoppers spend £10 at the supermarket. Wholesaler Decco supplies the products. The Federation of City Farms & Community Gardens will visit schools.
A Morrisons representative said: "We'll be launching a limited range from the catalogue next year."
TV garden designer Diarmuid Gavin, who is backing the campaign, said: "I'm keen to encourage children to grow fruit and vegetables and hope it will encourage them to eat more healthily."
The scheme closes on 27 November with vouchers available up to 31 October.
- See www.morrisons.co.uk/letsgrow