Theme: Honing Math
Skills in the Garden
Weather Matters
Considering Climate
Weather describes the variations that occur in the atmosphere
from day to day, while climate refers to the typical weather
found in an area based on years of observations.
To understand these concepts, it helps to understand what influences
climate. The most important factors are how warm an area is
and the amount of precipitation it gets. This, in turn, has
a big influence on the plants and animals that live there. Nearness
to the equator is the most important factor, affecting the amount
of sunlight, and thus warmth, that an area receives. Because
of the angle at which the sun's rays strike the earth, the equator,
which receives direct rays that pass through less atmosphere,
is warmer than locations nearer the poles.
Other factors that affect weather and climate are proximity
to water (particularly an ocean), direction of prevailing winds,
and relief (e.g., mountains). Consider, for instance, how these
factors influence climates in this country. The coasts tend
to have more moderate weather, with relatively cool summers
and mild winters, and less of a temperature range than the center
of the country. This occurs because the ocean, though it warms
slowly, holds heat and releases it more slowly than does land,
moderating the air temperature. The Midwest experiences cold
winters and very hot summers because the expanse of land heats
more quickly and cools more rapidly than water. It also tends
to be drier in the center of the country, since prevailing winds
from the west have lost most of the moisture gained over the
ocean. Mountain areas tend to get cooler temperatures and more
rainfall since thinner air is less able to absorb and retain
heat, and can hold less water. The Southeast, nearer the equator,
has hot summers and short, mild winters, and remains fairly
humid. The Southwest, though warm, is much drier since warm
moist air cools as it rises over the western mountains and drops
its moisture. The descending air is warm, but has little remaining
moisture.
Weather Up Close: Exploring
Microclimates
Ask your students if they have ever sought respite from the
heat under the cooling shade of a tree. If so, they've enjoyed
a microclimate.
Invite the class to brainstorm what the word microclimate might
mean, then try to agree on a definition or description. If necessary,
explain that it refers to the climate of a small, local area
that differs from the general climate because of differences
in sun/shade, temperature, wind, or moisture. Ask, What factors
might affect the climate in a given location? Then have
small groups investigate the school grounds, find places they
think might have different microclimates, and describe each
location. If you have the equipment, encourage groups to measure
rainfall or temperature differences in these areas. Which
is the warmest? Coolest? What might have caused the differences
(e.g., a building may provide shade and wind protection, dark
soil absorbs more heat)?
Factors that can affect microclimates include manmade features
like buildings and roads, geographical features like rocks,
slopes, or water runoff channels, or living things like trees
or meadows. A garden site on the south side of a building or
slope may get more sun and be much warmer than one on the other
side, for instance.
Investigate Plant Preferences
Ask your class how they think different microclimates around
the school might affect the growth of plants. Have them provide
a rationale for their answers (for example, plants might grow
more quickly in spot A, because it gets more sun and moisture).
How might they test or verify their hypotheses? For instance,
a group of students might start several containers of one type
of seedling (e.g., radishes, tomatoes, or marigolds) using the
same soil mix, container size, and so on, then place each in
a different location. They could track rainfall, soil, air temperature,
and so on, then chart the growth and development of plants in
each site. What can you infer about the effect of the microclimate
on plant growth? Were there other factors that might have influenced
the outcome?
Take Soil Temperatures
Is the soil temperature the same as the air temperature?
How might soil temperature affect plants? Invite students
to explore soil from different spots in the schoolyard. Do
some types of soil seem to warm up more quickly in the spring
than others? What are their characteristics? Have students
use soil thermometers to compare different types of soil, then
consider factors that seem to influence soil temperature. (Students
may discover, for instance, that dark soil absorbs more heat
than light-colored soil or that wet soil remains colder than
dry soil in the spring.) Help them grasp the concept that the
earth's surface heats up differentially, resulting in different
types of air masses that interact to affect climate.
Create a Garden Weather Station!
Meteorologists study the weather by recording data using a range
of instruments, then analyzing their findings. Consider cultivating
keen weather watchers by building your own garden or schoolyard
weather station.
A wooden or plastic weatherproof box can serve as protection
for your homemade or purchased instruments.
Water is vital to plant growth, so one of the weather factors
that most concerns gardeners is rainfall. (A good rule of thumb
is that garden plants should receive an inch of water a week.)
Challenge students to come up with suggestions for building
a rain gauge to track the amount of precipitation in a given
time period. For instance, find an old coffee can to hang out
at your weather station, then mark a clear plastic straw with
inches or centimeters (and fractions). Once a week, insert the
straw to the to the bottom of the can, put your thumb on top,
and withdraw it to read the depth of rainfall. Or make a tagboard
ruler and place it inside a clear glass jar. Cover the ruler
with clear cellophane or a sandwich bag and tape it at the top
to keep it upright.
Other weather instruments you can purchase from science suppliers
or make in the classroom include a psychrometer (to measure
relative humidity), a barometer (to measure air pressure), a
hygrometer (to measure humidity), a ventemeter (to measure wind
speed), a weather vane (to determine wind direction), and a
minimum/maximum thermometer (to measure temperature range).
For guidelines for creating some of these instruments from readily
available materials, check out the following Web site: (www.fi.edu/weather/todo/todo.html).
Blowin' in the Wind
An easy way to estimate relative wind speeds is to use the Beaufort
Scale. This system was developed to estimate wind speeds on
the ocean, and later adapted for land use. Consider having your
young wind watchers use the following scale, or create a similar
system themselves.
|
Observation
|
Wind Description (Speed)
|
| smoke rises vertically |
calm |
| smoke drifts; weather vane
inactive |
(1 - 3 mph) |
| leaves rustle; can feel wind
on face |
light breeze (4-7 mph) |
| leaves and twigs move; light
flags extend |
gentle breeze (8 - 12mph) |
| moves small branches; raises
dust, paper |
moderate breeze (13 - 28mph) |
| whole branches swaying |
strong breeze (25 - 31 mph) |
Explore the Lore!
Challenge students to consult families, gardeners, and weather
resources for examples of weather "lore." Which sayings might
have some scientific basis, and which are merely fanciful?
Ask students how they might research or test the accuracy of
these assertions. Some examples follow.
- If it thunders on All Fool's Day, it brings good crops of
corn and hay.
- Red skies at night, sailor's delight. Red skies at morning,
sailors take warning.
- If the woolly worm's head is more black than colored, the
coldest part of the winter will come in the first months of
winter.
- If oaks bud earlier than ash trees, it will be a wet summer;
if ash buds first, it will be dry in July and August.
- When you see a mackerel sky, 'Twill not be many hours dry.
- When it rains before seven, 'Twill clear before eleven.
Weatherwise School Gardens
"My seventh graders had created a blueprint for their dream
school garden, but realized they'd have to revise their plans
once they thought about the amount of sun required by their
proposed plants," reports Lostant, IL, teacher Jean Smith.
Jean's students had learned enough about climate to know that
the sun would shift positions throughout the year, and realized
they hadn't factored that into their initial plan. In March,
the students investigated where the school building's shadow
hit the garden site, then used what they knew of the sun's movement
to predict where the shade would fall in the summer. Each week,
the students drew an additional line on their original blueprint,
showing how the building shadow was progressing. "We used our
predictions of where the shade would hit to rethink which plants
we put where in the garden, based on how much sun each required,"
explains Jean.
School gardeners have lots of opportunities to think about
the influence of climate and weather. Although your students
might like to grow bananas in their school garden, for instance,
chances are that your growing season and climate conditions
wouldn't permit it. How does our climate affect what we can
grow and when we can grow it? How can we find a site that offers
at least six hours of sun a day? When is the danger of frost
past in the spring? Can we extend the season so we can garden
earlier in the spring? As your class plans to grow plants
indoors and out, seize the opportunity to examine how gardeners
notice and work with the climate and modify conditions for plants.
Zoning In
Many seed catalogs, packets, and gardening resources depict
charts or maps indicating conditions -- first and last frost
dates, average minimum temperatures, or amount of sunshine or
rainfall -- in different climatic zones throughout the country.
A commonly used map type assigns zone numbers indicating which
perennial plants can adapt to each area. If the winter temperature
in your area dips below a certain temperature, for instance,
certain tender perennials will simply not survive. Excessive
summer heat can also spell the end of certain plants.
Invite students to use gardening references or Internet resources
to examine different climatic zones throughout the U.S. Brainstorm
which geographic factors might influence the climate and, in
turn, zone designations. Some of the factors influencing climate
are proximity to equator (latitude), oceans, mountains, and
so on. Ask, Do the temperatures in your schoolyard or garden
reflect those in your zone? Have students regularly measure
high and low temperatures in these locations, then compare these
with temperatures in your local paper. Is your garden (or
other spot) warmer or cooler? What factors do you think might
affect this? How does this affect what you might be able to
grow?
Plant Cover-ups: The Greenhouse
Effect
Unlike many individuals, gardeners are people who actually do
something about the weather. That's because we like to extend
mother nature's growing season and we enjoy growing plants that
are not naturally adapted to our climates. (For instance, tomatoes,
a favorite garden crop, are actually native to tropical regions
of South America.) Many gardeners use strategies for extending
the season and protecting plants from frost and cold temperatures.
Cold frames, plastic milk jugs, and plastic or nylon row covers
keep sun-warmed air around plants and soil, prevent frost from
settling on plant leaves, provide wind protection, increase
humidity, and may protect plants from insects.
All these plant protectors operate on the same basic principle.
Radiant (light) energy from the sun can pass through transparent
and semi-transparent materials. When the light arrives inside
a closed space, it is absorbed by the surfaces within, then
radiated again as thermal (heat) energy. The heat energy is
less able to pass through the materials, so heat is trapped
inside. This energy warms the air, encouraging plant growth.
As a simple but powerful exploration of this phenomenon, invite
students to place a thermometer inside a clear, covered glass
jar in the sun. Place a second thermometer next to the jar.
After half an hour, compare the two temperatures. Once students
have explored this concept, invite them to try designing plant
protectors for their seedlings. Have them compare different
types of designs, predicting and then monitoring differences
in temperature and plant growth rates. (Although there are many
commercial products available, homemade gadgets can provide
a good design challenge for students.) Be sure that students
also consider other plant needs as they create and monitor their
setups. For instance, Is the temperature too high under the
plant protector? How can we provide ventilation? How can we
ensure that plants get enough water?
Predicting Frost
Concerns about frost damaging precious plants run high in the
spring and fall for many school gardeners. Challenge students
to check with gardening references, area gardeners, the Cooperative
Extension Service, or other local sources to find out the typical
last spring frost or first fall frost in your area.
Regardless of the weather station's prediction on a given day,
the microclimate in each garden is unique. Invite your young
sleuths to use what they've learned about factors that influence
weather to try to predict when a frost might occur.
When the sky is clear and there is low humidity, temperatures
may drop enough to cause frost. (Without clouds to act as a
blanket, the earth loses heat to the atmosphere.) To more accurately
predict frost, students can find out the dew point from the
weather forecast. When air cools to the saturation point (can
no longer hold water vapor), the vapor condenses and forms dew.
If the air temperature is below the dew point and below freezing,
frost occurs.
If your students are concerned about frost, but don't have
enough sheets or other materials to protect the whole garden,
encourage them to discuss which plants might need the most protection,
and why. (Typically, crops like tomatoes and peppers that originated
in warmer climates are the most sensitive to frost. Crops adapted
to cooler conditions, such as spinach, lettuce, and broccoli,
can handle modest frosts without damage.)
Author: Eve Pranis
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© 2008
National Gardening Association