KANSAS CITY, Mo. — Even after transforming hundreds of lawns — and doing it for nearly 40 million social media followers — this week’s job had this viral star nervous.

Spencer, the 26-year-old face of SB Mowers, posts weekly videos of him reclaiming and taming overgrown and neglected residential lawns for free. He said he goes by only his first name to protect his privacy.

He rose to online fame as the videos have gone viral again and again, often ending with shocked and grateful…