When Hilton Carter went to Tulum for his honeymoon in April he had to secure a sitter. The person needed to be responsible, demonstrate strong attention to detail and have plants proven to still be alive.

The 38-year-old artist living in Baltimore currently has about 180 plants in his home. And about 100 more in his studio space.

“You can’t just leave your plants with anyone,” he said. In the end, the plant sitter job went to a “dedicated friend.” One person declined, feeling it would be too much pressure.

People are pouring their hearts and wallets into houseplants, forming emotional bonds with ferns and Philodendron. Some call themselves plant parents. Friends call them obsessed.

Mr. Carter, who named the 15 plants that have been with him longest, including Monty, Francis and two Bobs, considers them “green pets.” Frank, a fiddle-leaf fig, is the oldest and has been with him for four years.