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"Within is a country that may have the
prerogative (advantages) over the most pleasant places known,
for large and pleasant navigable rivers, heaven and earth never
agreed better to frame a place for man’s habitation...Here
are mountains, hills, plains, valleys, rivers, brooks, all running
most pleasantly into a fair bay, compassed but for the mouth,
with fruitful and delightsome land...."
Captain John Smith, writing about Virginia
in his 1624 book, The Generall Historie of Virginia, New
England, and the Summer Isles
Virginia is blessed with a temperate climate,
moderate rainfall, and a rich and varied topography. Although
August sometimes feels unbearable in its humidity and January
endless with its ice and snow storms, these extremes ensure
that Virginians may enjoy all four seasons of the year. Who
would trade Virginia’s glorious and extended spring and
fall seasons for anything else? These conditions also present
you with an extensive plant palette. Without the January freeze,
no apple trees would thrive. Without the warmth of the remaining
seasons, camellias, cantaloupes, and persimmons would be lost.
Temperature, rainfall, and wind are the most
important aspects of climate, with temperature being the most
critical factor. Low temperatures late in the spring can destroy
a fruit crop. Unusually low temperatures in the winter may kill
plants that are marginally hardy in Virginia. There is a wide
variation in average temperatures across the Commonwealth, affecting
the growing season and your heating and cooling bills. Temperature
variations are affected by your land’s geographic position.
The temperature variations on land adjacent to the Atlantic
Ocean are more moderate than the temperature variations at the
peak of the Blue Ridge. Within these geographic areas, temperature
variations are also affected by the location and shape of a
site. The midslope of a hill has the most moderated temperatures
on a hillside. Look at a hillside and notice the location of
the first blush of light green when trees leaf out in the spring,
or notice where the trees first begin to turn color in the fall.
Remember that cold air drains down the drainageways just like
water, creating small frost pockets in its wake.
Plant hardiness maps have been developed for
all of North America by the U.S. Department of Agriculture.
Divided into 10 hardiness zones, these colorful maps are found
in most plant books. Knowing the zone number for your part of
Virginia will help you determine which plant will thrive where
you live. Virginia falls within Zones 5, 6, 7, and 8. This means
that plants native to the Pacific Northwest’s Willamette
Valley (Zone 7) will thrive in portions of Virginia. Plants
native to eastern Wisconsin, Illinois, and Massachusetts (Zone
5) may also thrive — although some may find Virginia too
warm — providing you with an extensive plant list from
which to choose.
Hardiness zones can be expanded or reduced
by manipulating the microclimate of a site. You can provide
wind protection for a plant or make use of a heat-absorbing
wall or brick terrace for reflected and stored warmth. The sun’s
position changes with the seasons, affecting the amount of shade
your garden receives. In summer, the sun is high in the sky
and casts short shadows. In winter, the sun is low and produces
long shadows. Study and chart your sun and shade patterns daily
and seasonally. You may also manipulate these patterns by building
structures. A broad eave or trellis will provide shade and create
a microclimate.
Much of the precipitation that falls to the
earth either evaporates back into the air from the plants and
ground surface or infiltrates down through the soil into the
groundwater. The remainder of the water runs across the surface
of your land into storm drains, streams, rivers, and lakes as
surface runoff. Once in the stream channel, it is joined by
subsurface flows at locations where the groundwater surfaces.
The prevailing weather pattern for Virginia
in the summer and fall is from the south Atlantic and the Gulf
of Mexico. Warm, moist air brings thunderstorms and higher humidity.
In fall, cooler air from the north and west returns. Winter
weather blasts across the state from the northern or central
part of the continent.
Plants benefit from a cooling breeze on a
hot day, just as you do. Wind keeps your garden’s air circulating,
preventing pockets of stagnant air, drying off the morning dew,
and reducing fungal growth on your plants. Wind can also harm
your plants. Too much, and the soft-wooded tree splits, or the
delicate leaves are shredded. Wind can also dehydrate the leaves
of the plant. If your home is on a windy hillside, your garden
may be a zone colder than the area in the valley below. Knowing
your prevailing wind patterns will help you avoid creating wind
tunnels or exposing vulnerable plants to inhospitable conditions.
Humidity is the moisture in the air and soil.
Plants that are happy in your summer garden most likely thrive
in high humidity. Choose fungus- and mildew-resistant plant
strains and provide your garden with good air circulation by
giving each plant adequate space to flourish.
Scientists have classified Virginia and the
rest of the United States into physiographic provinces. These
provinces describe the shape of the land (hilly, mountainous,
or flat); the type of rock found within it (sandstone, limestone,
or granite); and the type of soils commonly associated with
it. Four physiographic provinces are found in the Potomac River
watershed in Virginia.
Millions of years ago this area was underwater,
with the Atlantic Ocean extending west where Interstate 95 is
now located. Today the land is flat to rolling and is crossed
with broad, slowly moving rivers and streams generally flowing
eastward toward the Atlantic. Soils in this area are frequently
referred to as unconsolidated and are comprised of layers of
sand, silt, clay, and gravel originally deposited by ancient
oceans and rivers. Many of the soils in the Coastal Plain are
poorly drained and include “marine clay” or “blue
clay,” soil types that require specialized construction
knowledge. These soils shrink when dry and swell when wet, putting
great pressure on building foundations.
The fall zone of Virginia’s rivers is
located at the juncture of the Coastal Plain and the Piedmont
Provinces. Rivers that are broad and slowly flowing in the Coastal
Plain are narrow and filled with rapids and falls in the Piedmont
Province. The change from tidal to nontidal is reflected in
the creatures that live in and along the water. When Virginia
was first settled by Europeans, many of its river-sited cities
were located at the farthest point where ocean sailing boats
could travel upstream. Fredericksburg on the Rappahannock River,
Richmond on the James River, and Petersburg on the Appomattox
River are located at the fall zone. Historic Georgetown in Washington
D.C. is located at the fall zone of the Potomac River, with
Great Falls, Virginia, just upstream.
The Piedmont is the largest physiographic
province in Virginia and extends from the Coastal Plain to the
Blue Ridge. The shape of the land is rolling and forms the foothills
of the Blue Ridge Mountains. The Piedmont upland is dominated
by ancient igneous and metamorphic rocks, and the lowlands have
soils overlying shallow sedimentary rocks and igneous intrusion.
If you have ever hiked in the Blue Ridge Mountains,
you can easily remember the shape of the land in this province.
The steep slopes, stoniness of the soil, and the shallow depth
of soil above rock demand that careful attention be given to
minimize erosion. Soils in this province are derived from a
combination of sedimentary rocks, rocks formed directly from
the molten magma, and rocks formed by heat and/or pressure.
In general, the sedimentary rocks are on the west side of the
Blue Ridge, and the igneous and metamorphic rocks are on the
east side.
This province is primarily composed of sedimentary
rocks such as limestone, shale, sandstone, and conglomerates.
The depth of the soil varies tremendously. Sinkholes occur in
this area due to the nature of the bedrock.
Your yard, pasture, and common lands are located
on hills and valleys, on floodplains and uplands, and on the
slopes between. These places have distinctive shapes that provide
clues to the type of soil conditions you are likely to encounter,
what plants will thrive, and what potential erosion and drainage
problems you may experience. Soil surveys classify the soils
in association with their location on the particular shape of
the land, or landform. Typical soils in the Potomac River watershed
include Fairfax, Calverton, and Mecklenburg.
Floodplain: The floodplain is the area
adjacent to the stream channel that is periodically inundated
with water. Wetlands and floodplains also provide natural floodwater
storage, and their vegetation physically slows the speed and
turbulence of floodwaters.
Terrace: A terrace is an old alluvial
plain that is usually flat and borders a river, lake, or ocean.
Slope: Slope describes the tilt of
the land. Slopes influence land use and various environmental
components of the landscape. Stormwater runoff rates are higher
on steep slopes, and the performance of septic drainfields for
residential sewage disposal declines with steeper slopes.
Upland: An upland is generally higher
in elevation than the floodplain or terrace.
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