managing microclimates
If you garden indoors, you already
know that creating the right growing environment produces healthier
plants. Think of indoor gardening as
a premier, man-made microclimate,
a limited area within a larger locale
where somewhat different atmospheric
conditions are in effect. You’re familiar
with the idea of controlling the growing environment for indoor plants, but
when you move seedlings outdoors,
some of that control vanishes, right?
Well, maybe less than you think. By
understanding the microclimates in
your landscape, you can customize your
planting strategies, and maybe even
broaden your planting options.
What’s a Microclimate?
You already perform a little microclimate analysis in the garden. You know
the areas of your landscape that get
the most shade, for instance. A microclimate is a location where the prevailing climatic conditions vary slightly
from the norm. This can be the result
of one or a number of environmental
factors. For example, old-school growers pay close attention to spots where
frost and snow linger longest. It’s a
useful way to recognize areas most
susceptible to early frost or lowerthan-normal overnight temperatures.
Both low-lying and shady areas in the
garden can be microclimates because
the environmental conditions in these
locations are consistently different
from those in the garden as a whole.
Temperature
and Microclimates
Frost-prone and shady areas aren’t
the only temperature-related microclimates. For instance, urban locations
tend to be somewhat warmer than
their suburban counterparts because
concrete and asphalt absorb heat
during the day and release it during
the overnight hours, while areas near
lakes and rivers may experience slightly
cooler temperatures, especially when
there’s a breeze coming off the water.
The US Department of Agriculture’s
Plant Hardiness Zone chart helps many
gardeners decide which plant varieties to grow. It is so helpful, many seed
manufacturers print zone guidelines
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Maximum Yield USA | April 2015
right on their packaging.
Even though they are a
common and useful tool,
hardiness zones may be
a bit deceptive.
Geographical zones
are based on their
average annual low
temperatures, which
are calculated using
30 years’ worth of
weather data (from
1976-2005). The
numbers go from
coldest (1) to hottest
(10), and a difference
of 10°F distinguishes
one zone from the next
number up or down.
This means the
average annual
low temperature
for Zone 6, for
example, is 10°F
cooler than the
average annual
low temperature for Zone 7,
and 10°F warmer than what can be
expected in Zone 5. Although you may
not see it on seed packets, the USDA’s
zone designations are further broken
into 5°F divisions. Using our Zone 6
example, 6a is 5°F cooler than 6b and
5°F warmer than 5b.
Since just five degrees can separate
one zone from the next, temperature
fluctuations in your garden may compensate for that shortfall. Re-evaluating
your real estate based on its microclimates can throw parts of your garden
into a new zone, and also into a whole
new world of planting possibilities.
"Microclimates can be large or small, and
can include elements working alone or
in combination to modify the prevailing
conditions in portions of the garden."
Hardiness Zone
Game Changers
Buildings and hardscapes like driveways, patios and fences tend to make
adjacent areas warmer overnight. The
effect is enhanced if a building or
hardscape element also acts as a natural
windbreak and you’ve planted along the
protected side. Color can play a role,
too. White walls or fences reflect light
and heat during the day, while darker
colors tend to absorb heat and release it
as the temperature drops.
On the flip side, elevated spaces like
decks and patios can be colder than
normal, particularly when it’s windy.
Low-lying areas in the garden can also
be colder than expected. Cold air
is heavier than the warmer air aloft
and tends to pool in depressions and
downslope locations.
Microclimate Features
Although temperature can be an
important factor in microclimate
analysis, it isn’t the only consideration.
Microclimates can be large or small,
and can include elements working
alone or in combination to modify
the prevailing conditions in portions
of the garden. Let’s look at the most
important factors to consider when
identifying a microclimate:
• Urban development -- Proximity to
large buildings, roadways and other
urban features that retain heat can
increase the ambient temperature.
• Proximity to water – Lakes can
effect some major cooling and
less-pronounced cooling can occur
when breezes transit rivers, streams
and large ponds.