Smooth Ironweed is another popular choice for moist gardens. The tall, purple flowering plants are loved by all kinds of pollinators. It even hosts some larvae such as the Parthenice Tiger Moth. This plant can tolerate occasional flooding, making it an excellent choice for rain gardens. Ironweed is perennial and may self-seed into the garden, spreading over time. The bitter foliage is unpalatable to mammals, including deer.