Here are some ideas and sites related to gardens, planting and seasonal changes.
The first resource I always look to are parents, families, and your community. Check locally for a community garden, a garden club, or gardening business that would appreciate an opportunity to become involved in schools.
State universities and state extension services are also valuable resources. See the USDA Cooperative State Research, Education and Extension Service site as a starting point on the web.
I'd like to suggest a program called ‘Journey North’ as inspiration for pulling together art, science, and social studies in an integrated learning experience while networking schools together through the internet. The program is “a global study of wildlife migration and seasonal change” that can be adapted for grade levels, resources, and local habitat. One of the tools of “Journey North” is to plant tulips in the fall and record the bloom dates at locations across the nation to gain an understanding of the role of lengthening daylight hours for plants.
kidsgardening.org, a part of the National Gardening Association, as a parents and teachers sections for guidance in working with preschoolers.
AllSpecies.org - lots of community and enviromental education information including composting, and a project called EcoKids.
The Heart Forest - how this is a bit bigger than most gardens - it's a 22 acre site near the Kansas City International Airport. Consider a smaller scale “land art” - a school mascot or initials in herbs for instance. Check out land artist Stan Herd of Lawrence, Kansas, who helped us out with planning the Heart Forest.
While looking at the land art that is best seen from the air, think about other art that was only recognized when humanity took to the air - the Nazca Lines are geoglyphs in the Nazca Desert of Peru. And wouldn't you know it! - southeastern Peru is likely the “birthplace” of the potato!
Following this line of thought could be an introduction into Greek mythology and the story of Demeter and Persephone.
FYI - did you know that the Aztecs built “floating gardens” by piling soil on woven mats that were anchored to the bed of shallow Lake Texcoco, the site of today's Mexico City?