Governor Jay Inslee signed a new law allowing licensed facilities to provide “natural organic reduction”, which changes a body into roughly two wheelbarrows’ worth of soil over the course of several weeks.

Loved ones can keep the soil to spread or use it to plant vegetables or a tree.

Supporters of the method say it is an environmentally friendly alternative to cremation, which produces carbon dioxide while burial can pollute groundwater and takes up land.

Senator Jamie Pedersen, the Seattle Democrat who sponsored the measure, said the legislation was inspired by his neighbour, Katrina Spade, an architecture student who had researched the funeral industry.

She devised the idea of human composting, basing it on a practice farmers have used for livestock, and founded the firm Recompose in 2017.

Ms Spade used alfalfa, wood chips and straw to create a mixture of nitrogen and carbon that helps speed up decomposition.

From 2020, composting will become legal, along with alkaline hydrolysis, which is already legal in 19 other US states.