The giant hogweed is hard to miss. The monstrous plant towers up to 15 feet tall, with a crown of white flowers the size of an umbrella. They burst into bloom between the last week of June and the first week of July—just in time to be the perfect dramatic backdrop to red-white-and-blue-themed parties. But whatever you do, don’t touch it. The giant hogweed’s toxic sap could give you third-degree burns if you don’t get out of the sun and wash it off immediately.