This spring, on an impulse visit to a nearby nursery, I bought a rather pretty plant for my upper pond. It was a water hyacinth, which floats on the water, has interesting succulent leaves, and a beautiful blue flower.

If I had bothered to check my book Wicked Plants by Amy Stewart, I might not have been so surprised three weeks later when my pond looked like this:

Yikes! I wondered if it would be able to get out of the pond, come into the house, and eat one of my children in the night!

Apparently this lovely little plant is a pernicious weed that doubles in area every 2 weeks. According to Amy Stewart: “The crimes that this aquatic plant has committed are so great that it should be locked away forever – if only that worked.” She also says: “The plant is so horrible that it has earned its own Guinness World Record as the world’s worst aquatic weed.”

I probably would not have bought the plant if I had known this. And yet, as it turns out – no harm done. The hyacinths have produced pretty blue flowers all summer; the frogs love the pond, and our lower pond has never been so clear! Apparently the water strained through the hyacinth blockage comes out stripped of nitrogen – which feeds the algae that has been a constant problem in previous summers.

When I clipped some of the hyacinths out and threw them in the lower pond to see what would happen, they didn’t make out so well. Apparently even this hardened criminal of a plant could not withstand the mighty force of my voracious pond fish.

Have you ever invited a pernicious pest into your home by mistake? How did it turn out for you?