Fifty six community councils in Snowdonia are being urged to put off cutting the grass as a way of saving money and improving biodiversity.
Snowdonia National Park wants the grass to grow on areas including verges and lay-bys from the end of April, with trimming only in July and September.
The park is adopting the policy and is offering free wild flower seeds and plant plugs to councils.
But one councillor warned the move could affect accessibility.
"We know that this is a time of economic hardship, but sometimes doing less can achieve more," said Rhys Owen, head of the park's conservation and agriculture service.
"By encouraging growth and planting seeds in our communities we will see more flowers, more colours, more food for bees and animals, carbon will be reduced by not using machines and carbon will be stored by the plants," he added.
The park adds the change would offer schools a "good resource" in "illustrating life cycles".
"We will of course consider the safety of the public and their ability to see when deciding which areas will be considered for the scheme, and which plants will be suitable," Mr Owen added.
Dolgellau mayor Delwyn Evans said he wanted to see more detail of the plan.
"We haven't yet received the letter but my immediate reaction would be that not cutting grass could be quite unpleasant for walkers, and also the disabled," said Dolgellau town mayor Delwyn Evans.
"It could also look ugly, and I wouldn't want it to include cemeteries," he added.