On our flight into Chicago, I noticed the sign and made a mental note to check it out when we returned to the airport for our flight home. We luckily had a few extra minutes to spare and I was able to take a closer look.
Even if you are not a plant geek, you should venture to this area if you are in terminal G. The seating in this area seems to be the most comfortable and convenient (i.e. access to tables and outlets). There were few people using the area when I visited and it seemed like the perfect spot to knock out some work while you wait for your flight.
And, even if you are not a card carrying plant geek, you still might get a little jazzed to see this set up. The growing towers that hold the plants appear to be made of PVC pipe and there is a sophisticated system to provide light, water and nutrients to the plants. It is really fascinating to see all of the different plants that fit into the relatively small foot print of the growing area.