Introduction To Horticulture & Plant Physiology

 HORTICULTURE DEFINED

Horticulture is defined by Webster’s dictionary as

“the science and art of growing fruits, vegetables,

and flowers.” It is the intensive commercial produc-

tion of high-value and high-yielding plants. But it

also includes the cultivation of garden crops and

landscape ornamentals and the interaction of science

and art.

Horticulture contributes to the economy, provides

good nutrition, and is a valuable spiritual and psy-

chological therapy. Horticulture beautifies and

enhances the environment. Areas of horticulture

include the following:

· Pomology. Fruit culture, including pome fruits

(apple, pear, quince), stone fruits (peach, cher-

ry, plum, nectarine, apricot), small fruits (blue-

berry, raspberry, grape, strawberry), and nut

tree fruits.

· Vegetable production. Culture of food crops

from vegetable plants including roots, fruits,

and seeds.

· Floriculture. Growing of cut flowers, potted

plants, bedding plants, and bulbs and floral

design.

· Environmental horticulture. Nursery produc-

tion of herbaceous and woody plants for land-

scape design and management.

· Postharvest physiology. Harvest, handling,

and storage of horticultural crops including

flowers, fruits, and vegetables.

CLIMATE IN HORTICULTURE

Macroclimate

The term “climate” refers to the long-term weath-

er patterns of a large geographical area and is used

interchangeably with “macroclimate.” Macroclimate

is determined mainly by an area’s latitude, eleva-

tion, nearness to large bodies of water, nearby ocean

and wind currents, relation to nearby forests and

irrigated areas, and location in relation to topo-

graphic features such as mountains.

Temperature and light are two fundamental fea-

tures of climate that profoundly affect gardening.

Rainfall, wind, hail, clouds, snow, and humidity also

create the climate of a region. Short-term variations

in rain, wind, snow, and other climatic characteris-

tics are the weather.

Climatologists have calculated the statistical

probabilities of certain climatic occurrences that are

likely to affect plant growth. The USDA hardiness

zone map, for example, is based on an area’s aver-

age minimum temperatures. The Arbor Day

Foundation has produced an updated version of the

climate zone map based on the last 15 years of

warmer temperatures (1990-2005) (figure 1).

Microclimate

Microclimates are variations in climate within a

community, yard, or other restricted area and result

from topographic features, soil types, aspect, or

location of buildings, fences, and/or plantings.

Different microclimates will be more or less con-

ducive to different outdoor activities and will limit

or enhance the success of plantings. For example, a

shady northern exposure may make a better summer

patio space than the sunny south side.

Gardeners can create or modify microclimates to

increase livability and diversify planting conditions

on their property. Landscape features that produce

microclimates include the following:

· Hills and low areas. Hillside locations are less

subject to frost since cold air is denser than

warm air and will flow downhill to settle in

low areas. A south-facing slope warms earlier

in the spring than a north-facing slope, but will

be hotter and dryer during summer. The lee-

ward side of a ridge is less subject to wind or

breeze than the windward side.

· Structures. Structures such as buildings,

fences, driveways, or sidewalks serve as heat

sinks for solar radiation. Planting areas around

them will be warmer, especially on their south-

ern sides or next to pavement. Northern sides

of buildings and fences are shady and will

remain cooler and moister.

· Bodies of water. Water has a moderating

effect on air temperatures. A lot more energy is

required to raise the temperature of water than

the temperature of air. Likewise, water releases

large amounts of heat energy when it cools.

Thus, water acts as a buffer to heat or cold.

Air blowing over cool water will cause adja-

cent land to warm up slower in the spring, thus

delaying bloom and growth. This can protect

plants from spring frosts. In the fall, air moving

over warm water keeps the surrounding land

warmer longer than areas farther away.

· Elevation. The higher the elevation, the cooler

the temperature; there is less atmosphere to

retain the heat from solar radiation at high ele-

vations. Each 300-foot gain in elevation results

in an average 1°F drop in temperature.

· Raised beds. Raised beds heat quicker than

surrounding flat soil surfaces, but plants in

raised beds may dry out faster and suffer root

damage due to freezing in winter.

· Plants. Large plants create microclimates by

reducing wind speed, creating shade, and rais-

ing the humidity beneath them.

· Soil. Sandy soil will warm more rapidly in the

spring than clay soil and can be planted earlier,

resulting in a crop that will mature more rapidly.

By identifying and using microclimates to your

advantage, you can maximize the conditions for

individual plants or strategically locate garden beds,