Ideal World horticultural buyer James Carter said the split happened last week and insisted there are "no hard feelings". New serious budgets are hard to reach and he cannot see that happening with one vendor, he added.
Thompson & Morgan left QVC for an exclusive agreement with Ideal World in 2014 but other suppliers have since come to the channel.
Carter said Ideal Shopping Direct has a £10m turnover in gardening, with 40-50 per cent accounted for by plants. Adam Walcott and Angela Noghani are among its gardening presenters.