Haiku celebrates nature and is best written in the moment of observation, so why not take your students out for a GINKO, a Haiku Walk?
Before your walk, teach students the basics of haiku: The 5-7-5 pattern. Keen objective observations recorded in the present tense. Haiku's lack of title, rhyme, simile, metaphor, etc. Traditional haiku's subjects: the natural world, seasons, links to human nature. Haiku's need for concrete, juxtaposed images, and for a the reader to experience a bit of surprise.
Read them Japanese Masters: Issa, Basho, Buson, Shiki. Read them Modern Masters: Kristin O'Connell George, Jane Yolen, Alice Schertle, Janet Wong, and many others.
With pen and paper in hand, help your students notice the little things. Help them get their ideas on paper before attempting to bound them to form. Help them become Haiku Masters.
P.S. I am currently writing a picture book that will show children not only how to write, but why to love, Haiku.