Even though it takes place in a hospital room, pretty far away from the natural world, "Tulips" is packed with natural images. To start with, there are the tulips, which excite and upset the speaker's mind. Beyond that, there are images of seagulls and water and rocks and wild cats. Even the sun pops up a time or two. So why all this natural imagery in a poem that takes place in a sterile hospital room? For one thing, these images help to blend the outside and the inside, to bring the rhythms and images of the natural world into the closed, cold world of the hospital. Plus, don't forget that our speaker yearns to be free. And what could be freer than a seagull, flying over the ocean?
The tulips are threatening to the speaker because they combine the wild unpredictability of nature with symbols of love, family, and attachment.
The natural images in this poem reinforce the painful unpredictability of life. A thing like water can be comforting and soothing one moment, and violent and murderous the next.