Parking lots are the latest target of Mayor Bloomberg ‘s green thumb.

The city this week proposed new regulations for commercial parking lots that would require new and expanding lots to intersperse canopy trees among parked cars and provide green landscaping around perimeters of the lots.

Open lots with 36 parking spaces or more would be required to plant one tree for every eight spaces to create a shady, pastoral effect over the asphalt terrain, which also increases the city’s heat index during the summer.

Parking lots with 18 parking spots or more would be mandated to surround their perimeters with greenery. The green parking lot initiative is one of 127 proposals Mr. Bloomberg has outlined in PlaNYC, his roadmap for preparing the city for an expected influx of one million new residents by 2030.

“Where you find your open space in a city is going to be either an existing park or parking lots,” a professor of landscape architecture at Louisiana State University, Buck Abbey, said in an interview. “Parking lots have been designed for big cars, but if we move toward smaller cars we can squeeze extra space to get some landscaping in there.”

Landscaping at parking lots would also keep rainwater out of the city’s sewer system, a spokeswoman for the Department of City Planning said. Cities such as Chicago and New Orleans have preceded New York in adopting landscape codes to green their parking lots.

The push to beautify the city’s parking lots is raising some concerns among small business advocates. “To raise the cost on neighborhood businesses in the name of the environment while promoting large-scale shopping centers is an environmental sham,” a spokesman for the Neighborhood Retail Alliance, Richard Lipsky, said in an interview. “We should worry less about how many plants are going into neighborhood parking lots and more about how we sustain small businesses against box stores. That is real sustainability.” The public review process is expected to take about seven months.