The NWC was founded in 2001 and became part of the Eden Project in 2017 with the aim to create new landscapes for people and pollinators.
Juliet Rose, head of development at the Eden Project, said she hoped the competition would bring more attention to wildlife.
She said: “Biodiversity is in crisis and people are less connected with nature than ever.
“We hope that by marking the NWC’s 25th anniversary with this competition, the vital importance of wildflowers will be brought to the public’s attention, while also celebrating their remarkable beauty.”