Hyacinths will not make it outside for sure. Take them out as they die off so they do not pollute your water. "One with purple flowers". Hmmmm. Is it rooted from the bottom of your pond? Did it come from someplace local? A picture or more of a description will help us figure it out. The only plants I bring in or throw away in my pond are hyacinth, taro and elephant ears. Most lilies, pickerel, lizards tail, water cannae, parrots feather, rush and cattails will make it through. Just try and make sure the roots do not completely freeze.