When winter come,cover these plants with film bag,fill CO2 into the bag.or to move the plants in room.

Around here they get composted.

Due to a language barrier, no doubt, design has once again missed the whole thrust of an inquiry.

I only knew of one commercial landscaper. Anything "exotic" or zone improper in an outdoor installation was, in effect, a loaner and removed and stored over in a commercial greenhouse.

Or maybe what you saw were caladiums, elephant ears, castor beans, etc. - any or all of which can be pretty exotic looking, but easily grown on a seasonal basis.

When I lived in Illinois, I saw certain planters on the streets of the Loop with enough regularity that I can say the plants were changed at least two or three times a year.

It was always my assumption that the City had a contract with someone (or several someones) to provide the landscaping ... and I never had any illusions about what happened to the plants once they were removed. Most of these were annuals which wouldn't have lived through the winter, but some were perennials like chrysanthemums.

As to details, I can only add that there was quite a bit of variety from one block to the next. They made considerable use of pine boughs in the winter to fill up the planters. One season a planter I used to see often was filled with ornamental cabbages; a few disappeared, and I wondered if some savvy homeless person was enjoying some particularly fresh vegetables for dinner....

It would most likely depend on the actual individual value of the plants being used as well as the species. Winter deciduous stuff might be dug up and stored for use the following season, expensive and/or slow growing palms or other species might also be planted as plunged pots, and simply dug up and moved back into greenhouses. What complicates saving and re-use for the following year, is the fact that insect pests also can follow the plants, and become typhoid Mary's for your existing house plants. Even if you do find out from the business owners or there landscape maintenance companies that the plants will be dumped at the end of the season, the plants aren't necessarily a bargain if you aren't able/willing/knowledgeable about how to prevent or more likely at best, minimize the pest problems. I'd avoid bringing anything inside if it will present problems for high value plants you already own, and get familiar with combatting mealybugs, spider mites, fungus gnats, aphids, white flies and scale, to name just a few of the most common uninvited guests...