By all accounts, Ida Severson is tough as nails. But after more than two decades in the landscaping business, she’s eager to embark on a new chapter that isn’t so damn hard on the back and knees.

The opportunity to open a nursery has finally arrived: On Oct. 1, she took over the 54 B Street location that had been occupied by Mostly Natives. Sometime before Thanksgiving, she will launch her own nursery there: The…