In July 2011, a month after hail—golf-ball-size and larger—demolished 13 greenhouse roofs at the Garfield Park Conservatory, Mary Eysenbach, director of conservatories for the Chicago Park District, got a postcard from a contractor: “You may have hail damage and not even know it.” With estimates saying the hail had shattered 31,000 panes of glass throughout the West Side institution, Eysenbach knew it, all right. Four years and roughly $15.5 million later, the sprawling conservatory, one of the largest in the country, reopens its restored 107-year-old glasshouses on April 22. The iconic Fern Room (pictured) required the most work, with 80 percent of its panes having been destroyed. Most of the plants survived the tempest but took a bigger beating during cleanup as workers tromped through the beds. See above for how the room was rebuilt in keeping with famed landscape architect Jens Jensen’s original vision—but fortified to better withstand future storms.

As staffers moved plants out of the way of construction, they discovered stonework around the Fern Room’s perimeter that mimicked natural rock formations, concealing pipes and wiring. The conservatory plans to keep the stone exposed.

1. The wood framing was reinforced with steel because the new glass is heavier. Wood from cypress trees, which grow in swamps, was used for the new trusses, just as it was for the original ones, because it’s waterproof.

2. Workers handpicked larger debris from the soil before descending on the fern beds with vacuum cleaners. To this day, Eysenbach finds small shards of glass almost every time she enters rooms that were damaged.

3. The new glass is double laminated, a quarter-inch thick, and tempered like a car windshield. It might crack in another colossal hailstorm, but it won’t shatter. Each pane had to be cut by hand to specific dimensions to fit the imperfect original wood trusses.