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Challenge
students to work outdoors in small groups to identify examples of decomposition in action. Have
them describe what they observe that leads them to think decomposition is occurring.
To find out what your students know or assume about this relationship, ask, Plants need soil, but does soil need plants? Record their speculations and supporting reasoning, then suggest they explore outside to make observations. They might break up into teams to explore soil in areas with different types of vegetation (e.g., garden, lawn, weedy patch, woods), or those with different degrees of plant cover (e.g., a compacted area along the edge of the driveway or sidewalk vs. a less-traveled area of the playground). Each
team can record its observations and report them back to
the class: “There was a thick layer of rotting
leaves under the trees,” “There was a gully in the steep
bank,” or “Grass roots are hard to dig through!” Have them
use other senses, too: record the texture and moistness
of the soil, and even the odor (if they’re game). Also,
did
they find insects and worms, or evidence of them? Do their
discoveries support or contradict their initial assumptions?
Is there anything that inspires them to dig deeper into the mutually
beneficial relationship between plants and soil? Consider
asking small groups to create presentations (e.g., slide
show, PowerPoint project, play, poster)
describing their findings and any inferences or conclusions they've drawn. What About Weeds? Ask your
class if they think weeds have a role in nature, and if
so, what it might be. They might want to
test the value of weeds as a soil
cover by allowing them to take over a small corner of
a garden bed. Let them grow (though we advise removing seed
heads before they drop their bounty) and during the growing
season, compare the weed
patch soil
to
that
of
the cultivated
garden. Note the amount of soil surface covered with
plants, soil texture, number and type of soil creatures,
and so on.
They might brainstorm other tests,
e.g., comparing a mulched plot, a weeded plot,
and a plot where weeds rule.
Copyright© 2004
National Gardening Association
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Classroom Project
Sparking Curiosity for Decomposition
Some Favorite Books and Curricula
NGA's Guide for School Garden Entrepreneurs
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If this is your students’ first experience with decomposition
concepts, here are some suggestions for stimulating curiosity
and inquiry.
Without
plants, the land would be a desert: a barren surface,
unprotected from the effects of sun, wind, and rain. Besides
protecting soil from the elements, when they die, plants
supply worms, insects, and microbes with the raw material
to build
humus, rich in nutrients that support a robust soil food
web. (Recently, researchers discovered that living plants
secrete
excess
carbohydrates
through
their
roots
to encourage
growth of microbes!)
We call a plant a weed if it's growing where we don't want
it to grow. The fact is, what we often call weeds are
just plants doing exactly what they've evolved to do:
take advantage
of available growing space. (And they’re very, very good
at it, which is why we don’t want them in our gardens!)
In the process, many prevent erosion and weathering of
the soil, and if left to grow, will actually improve
texture and nutrient content, making it possible for
other kinds
of plants to grow and thrive. (Fallowing – allowing
a cultivated field to lie undisturbed for
a
period of
years
– takes
advantage of the soil-building ability of colonizing
plants.) In general, undisturbed weed patches will
yield to another
kind of vegetation as ecological succession marches on. 
A "hot" compost
pile is
a dynamic environment ripe for measurement, tracking, and
graphing. (For details on cooking up a "compost
cake," read 
