"In the beginning of the school year, I ask my fourth graders to bring in any kinds of seeds they find outdoors, then we plant them and observe what happens," says teacher Tom Murphy from Farmington, MN. When students discovered that garden seeds like marigolds sprouted quickly, but few seeds from native trees such as walnuts and oaks began to grow, the stage was set for a year-long investigation. "Students wondered why the tree seeds didn't sprout," says Tom. "This prompted a discussion about what might happen if seeds of native plants were to germinate in the fall in our cold climate." Students inferred that young tree seedlings might not survive the winter, and brain-stormed how they might simulate winter conditions for the seeds, to see if they could encourage them to sprout in a GrowLab "spring."
The class collected what they assumed were tree seeds and subjected them to different simulated winter conditions. Students put some seeds in refrigerators or freezers buried in moist peat moss in bags. They placed others in moist peat moss in mesh bags, and buried them in a garbage can six inches under the ground. Some seeds remained unchilled in the classroom for comparison.
Between January and March, students removed seeds from their "winter" locations, planted them in soilless mix, and placed them in the GrowLab. "The students were so surprised when many tree seedlings -- black walnuts, acorns, American chestnuts, maples, and catalpas -- actually began to sprout in the classroom," reports Tom. As students had predicted, most of those that didn't experience "winter" failed to germinate. Students tended the GrowLab arboretum, then transplanted seedlings out to a garden "nursery" in the spring when the plants were six to ten inches tall.
Students discovered, says Tom, that some tree seedlings such as black walnut sent down a long taproot that began to wrap around inside the pot if left too long. They learned through research and trials that it helps to prune back the tops of seedlings to just a few leaves before transplanting, to balance the effects of damaged roots. (With fewer root hairs to take up water, he explains, it's important to cut down on the volume of leaves that will be transpiring water.)
The following year Tom's new students were invited to begin the cycle again by bringing in tree seeds, then taking home an "adolescent" tree seedling from the previous year to plant at home or in a community location. "Not only did this project encourage students to use science process and problem-solving skills, but it really got them thinking about how native plants evolve and adapt over time to different environmental conditions. And I know they're now much keener observers of trees and all different types of wild seeds."
Tree Seed Tips
We've heard from a number of teachers whose students have raised tree seedlings in classroom gardens to link with broader outdoor explorations of trees. It's easier to sprout some tree seeds than others in the classroom, but hard to come up with a "foolproof" list. Some, like many of those tested by Tom's students, require a period of chilling in a moist medium like peat moss. Others, like the thornless honey locust, typically sprout best after being mechanically scarred. Still others, such as different types of white oaks, don't seem to require any special treatment to sprout.
Tree seeds that we've heard to be successfully germinated in classroom gardens include red pine, Douglas fir, Colorado spruce, thornless honey locust, red and silver maples, black walnut, American chestnut, white oaks, and apple. There are certainly others that your budding young scientists can coax to sprout in the classroom. Please let us know of your tree seed experiences so we can share them with other growing classrooms.