Once dubbed the dirtiest city in the world by the UN in 1992, Mexico City has taken a number of steps to go green.

In the past two decades, they’ve implemented “No-Drive Days” and opened a large bike-sharing system. The city, however, still remains in the top 40 most polluted cities worldwide. In turn, citizens have called for a more drastic environmental change. Born out of a Change.org petition that collected 80,000 signatures in 2016, Via Verde, a project that turns highway pillars into vertical gardens, is making Mexico City into an emerald one.

The project, which translates to the “Green Way,” grabbed about half a million views in a video posted by ATTN: to Facebook on Monday, adding to the 22.5 million views the clip has accumulated from another post a week before. The video stars an ambitious greenscaping endeavor launched in 2016 in Mexico City to transform over 1,000 pillars on its main highway into vertical gardens, with the promise of helping the city clean its air.

via verde column
Each column is supported by an automatic irrigation system.

How Concrete Becomes a Garden

Once completed, the 27-kilometer project boasts that it will filter 27,000 tons of harmful gas, provide clean oxygen for 25,000 citizens per year, and capture 11,000 pounds of dust. But the bigger impact on morale may come from turning the grey columns green: Research shows that exposure to green spaces can be mentally restorative. The TomTom Traffic Index ranks Mexico City as the most congested large city in the world. By turning the columns into a greenspace, it could lower the stress levels of commuters who frequently use the highway.

recycled bottles into felt
The vertical gardens will reuse recycled bottles to create the hydroponic felt from which plants can grow.

To achieve the feat of beautifying 600,000 square feet of concrete pillar, Via Verde developed a felt fabricated from plastic bottles that matches the density of soil, sewed by local inmates as social rehabilitation. The plants may not need soil, but they will require water.

“We’re not using a single drop of drinkable water,” says founder and architect Fernando Ortíz Monasterio in the video. The gardens will make use of the highway’s large surface area, collecting and filtering rainwater to sustain the gardens.

How Green Are the Gardens?

Critics complain that the garden qualifies more as a cosmetic gimmick than a commitment to environmental change. By transforming a space primarily used by people driving cars, the projects fails to address the pollution emitting from the use or production of cars themselves.

Some citizens also doubt the columns’ ability to deliver the oxygen promised. One of the project’s main talking points emphasizes the oxygen generated by the plants, a process called phytoremediation. But of the plant species identified by Via Verde, only a few can produce oxygen at rates promised by the project.

tree vertical garden cost
This image, circulated on social media, compares a single vertical garden column to the number of trees planted for the same price: 300. 

Even more simply, an image circulated on social media draws a starker question: Why doesn’t the city simply plant trees instead? Three hundred trees could be planted with the resources invested into a single column.

Self-described “capitalist-environmentalist” Monasterio admits that the carbon reduction impact of the project is negligible. Roberto Remes of Mexico City’s Public Space Authority points out that it was “never the intention” of the project.

However, the project still earned a 93 percent approval rate from the public, according to AltoNivel. And it’s not even complete yet — construction for the gardens began in 2016, aiming to complete 545 columns by 2018, leaving the remainder for 2019.

While the green transformation continues, Monasterio’s project has attracted global attention, from Japan and Germany to Argentina and Colombia. A vertical garden could soon come to a highway near you.