Horticulture differs from agriculture or forestry in that there is more intensive management where the individual plant is important and there is a higher gross return per unit area per time.

Horticulture..the cultivation of a crop that is highly valued and intensely managed where the individual plant matters

History of Horticulture

Cultivation of edible plants began 7,000 to 10,000 years ago.

Agriculture lead to an available and dependable food supply, which in turn lead humans to be able to become scientists, artists, and engineers. All quality of life increased.

Around 3,000 B.C.E. preparation, irrigation, and pruning of plants took place in Egypt. Irrigation lead to the ability to create extensive and planned gardens

Irrigation spread through Mesopotamia, Babylonia, and Assyria and by 1800 B.C.E. 10,000 square miles were under cultivation to feed 15 million people.

Greek philosophers contributed to the study of crops, such as Theophrastus, who is considered the father of botany.

Romans made no major horticultural advancements, but they did use and improve on the technology of conquered peoples. This included grafting, budding, legume rotation, storage of fruits and vegetables, and the creation of the first greenhouse-like structure.

Arabian cultures established botanical gardens between 800 and 1300 C.E.

Monks perpetuated science through the Middle Ages and the Renaissance period brought forth new scientific discoveries.

There are many ideas regarding how humans developed agriculture, including various cultures believing it to be a divine gift.

Early societies grew figs, dates, grapes, and olives as well as roses, ornamentals, and medicinal plants.

The Chinese developed cultural practices for tea, oranges, and Ephedra.

In the Americas, Pre-Incans in Peru cultivated corn, potatoes, cacao, tomatoes, peppers, and beans about 5,000 years ago.

Norman Borlaug

Borlaug lived from 1914 to 2009 and fathered the Green Revolution

Borlaug is credited with prevented the starvation of one billion people by developing disease resistant wheat varieties for tropical nations

Green Revolution

The Green Revolution occurred from the 1940s to the 1970s when populaitons were rising and crop yeilds were stagnating

The Green Revolution arose out of necessity and resulted in the modernization of agriculture, leading to enhanced crop yields, increased food security, and reduced hunger.

Timeline

8000 B.C.E..domestication occurs
3500 B.C.E..Egyptians begin using irrigation
1492..European discovery of the New World
1800..Chemical fertilizers first used
1862..US Merrill Land Grant College Act establishes agricultural institutions and the USDA is introduced
1866..Mendel describes inheritance
1887..The Hatch Act established an agricultural experiment station in each state
1930..the first plant patent is given
1970..Normal Borlaug fathers the Green Revolution
1982..the first GMO crop is created

Recent Advancements

New cultivars are continuously improving crop quality and yield as well as pest and environmental resistance.

Created understanding of plant-water relationships helps improve the efficiency of irrigation systems.

Light can be used to trigger or delay flowering.

Temperature control increases production efficiency of greenhouses.

Plant nutrition improves through fertilizers delivered in specific ways at specific rates.

Rhizosphere soil-free mixes

Integrated pest management is more environmentally friendly.

Plant growth regulators can be applied to control height, branching, flowering, and fruit size

Horticultural engineering can automate processes and implement remote sensing.

Post-harvest refrigeration and controlled atmosphere extends the viability of food.

Lecture 2: Careers and Classification

Diversity of the Horticulture Industry

There are numerous ways that one can find a career in horticulture:

Creating and distributing supplies such as pots, chemicals, tractors, and processing equipment
Grower services including pest control, nutrient analysis, and greenhouse maintenance
Production of crops includes skilled and unskilled labor, GMO creation, and tissue culturing
Marketing of crops is crucial, as producing a crop is useless if there is no market for it

Horticulture in the U.S.

In 1862 the Morrill Act was signed and the USDA was created, causing a boom in horticultural research

The Hatch Act of 1887 led to experiment stations in every state

In 1889 the US Department of Agriculture was elevated to cabinet status

Areas of Horticulture

Furthering studies in horticulture can include plant sciences, animals science, engineering, and social sciences

Horticulture is closely related to applied plant sciences and agronomy, as well as forestry.

Horticulture can be broken down into three sections:

Ornamental horticulture
- Floriculture
- Landscaping
- Interiorscaping
Olericulture (vegetables)
Pomology (fruits and nuts)

Ornamental Horticulture

Ornamental horticulture..growing plants for natural beauty

Floriculture..production, transportations, and use of flowers and foliage plants

Floriculture accounts for more than half of all non-food horticulture.

Floriculture crops are primarily grown in greenhouses in temperate climates and are very time sensitive, including Easter lilies, poinsettias, and Christmas cactus.

Landscape horticulture..production, design, and marketing of landscapes

Nurseries are very important in landscape horticulture.

Interiorscaping..growing plants for inside usage, including indoor malls and medical offices

Olericulture

Olericulture..vegetable production, harvesting, storage, processing, and marketing

Olericulture is very complex and competitive.

Pomology

Pomology..growing, harvesting, storing, processing, and marketing of fruits and nuts

Post-harvest preservation is a major aspect of pomology

Examples of Careers

Many jobs are available within horticulture including:

Florist
Golf course superintendent
Cooperative extension specialist
Crop consultant
Teaching
Research
Botanical gardens and arboreta
Landscape architect

Classification of Horticultural Plants

Theophrastus was the first person to classify plants

Carolus Linnaeus was the creator of the current classification system that is now regulated by the International Code of Botanical Nomenclature

The classification system assigns organisms into kingdom, phylum, class, order, family, genus, and species (King Phillip Came Over From Germany Stoned)

Scientific names are typically preferred over common names as common names can be misleading and refer to a number of different species.

Grouping Horticultural plants

There are many different ways to group horticultural plants together

Dicots vs. monocots
- \
Kinds of stems
- Stem types are described as physical hardness
- Herbaceous..stems that are not woody and are short lived
  - Vines..herbaceous plants that twine
- Woody plants..dense, sturdy, long lived plants
  - Liana..woody plants that twine
Climate
- Warm season and cool season are often categories used for grass and vegetables that define optimal conditions for growth and survival
- Plants can be cold hardy or tender
Soil moisture
- Hydrophytes..aquatic plants such as water lilies
- Xerophytes..drought tolerant plants such as cacti
- Mesophytes..plants that prefer intermediate soil moisture, a group including most plants
Unique characteristics
- Halophytes..plants that thrive in high salt soils
- Basophilic..plants that prefer basic soils
- Acisophilic..plants that prefer acidic soils
Life Cycle
- Annuals..plants which go from seed to seed in one season
- Biannuals..plants that have a two season life cycle
- Winter annuals..plants that germinate in the fall, overwiner, and flower in the spring
- Perennials..plants that live two or more seasons
Foliage
- Deciduous..plants that drop their leaves
- Evergreen..plants that hold leaves all year long
Usage
- Edible..plants whose primary usage is consumption
- Amenity..plants that provide aesthetic primarily

Terms

Forma..subdivision of a species differing only slightly

Variety..subclassifications of the traditional species

Plant varieties are listed as the genus and species name followed by their variety, such as Scilla sibirica var. alba.

Cultivar..a group of plants within a species often distinguished by flower, fruit, or vegetative characteristics that can be patented

Cultivars can be listed of ‘Hidcote’ or cv. Hidcote, but should be kept separate.

Hybrid plants names should be preceded by a capital X (Petunia X hybrida)

Cultigen..plant or group of plants originated in domestication with no native form

Cultigens include brussels sprouts, cabbage, and corn

Line..sexually reproduced cultivar

Clone..population of plants derived asexually from one individual

Lecture 3: The Plant Environment and Light

Plant Environment

Horticulture is the manipulation of plants and their environment

Plants are bred for particular characteristics and growth

A plant’s environment includes both abiotic and biotic factors

Atmospheric environment includes wind, light, temperature, and rainfall
Edaphic environment refers to underground conditions

Plants are influenced by genetics primarily and their environment secondarily. Their environment impacts growth and development.

Wind

Wind is an abiotic facor that impacts aboveground plant growth

Higher winds lead to plants that are smaller, more compact, and with a tougher cuticle.

Wind cools a plant, reduces moisture, and reduces disease by making plants more resistant to mechanical stress, pathogens, and pests

Wind can cause destruction of plants, spread spores, pests, and seeds, and cause salt spray.

Light

Light is majorly important to plant growth

Light can be defined by its itensity (quantity), color (quality), and the length of the dark period (photoperiod).

Quantity

Light quantity..the amount of light within particular wavelengths

The main source of light for plants is the sun and the highest amount of light is at noon.

Light can be absorbed or reflected off of a leaf; only a small amount is used in photosynthesis

Photon..discrete particle of energy

Light compensation point..where carbon dioxide fixed by photosynthesis is equal to that lost by respiration. At this point a plant maintains tissue but does not grow.

Light saturation point..the point where light is no longer the limiting factor. Varies by species and number of leaves per individual.

Quality

Light quality refers to its wavelength

Plants absorb light from the visible spectrum. Chlorophylls, carotenoids, and phycobilin absorb light from specific wavelength

Leaves absorb blue and red light and reflect green light.

Photosynthesis

Photosynthesis takes place in the chloroplasts.

Light reactions are driven by light energy and occur in the grana.

Photosynthesis required carbon dioxide, water, and light, and yields glucose and oxygen as a waste product.

Stomatal opening is regulate by guard cells and facilitates carbon dioxide entering the leaves as well as water exiting.

Spacing and Orientation Issues

Field plants need to be spaced ideally for maturity. This leads to wasted space when plants are young.

As a rule of thumb, bigger plants should be placed in the back or to the north and smaller plants should be in the front or to the south.

Pruning

Horticultural crops are often pruned for enhanced light interception, particularly for more light to hit the middle of the tree.

Pruning properly allows for more photosynthesis, more sugars, higher yields, and more fruit color.

Ornamental hedges are pruned for aesthetic, but also light capture. Keeping bottoms wider ensures that the tops don’t shade lower leaves.

Etiolation

Etiolation..exaggerated plant stem growth in the absence of light

Etiolatoin results in visible internode elongation and yellow tissues

Etiolation does not occur in monocots, rather leaves just get bigger

Cuttings from etiolated leaves root easier

Blanching..when plants or plant parts are covered to be devoid of light.

Cauliflower heads are covered with leaves to keep the head white in an example of blanching.

Plants can etiolate in response to blanching treatment

Phytochrome Response

An excess of red and far red light can lead to phytochrome responses in plants. This is a light quality issue.

Phytochrome resonses are essentially etiolation, but due to lower quality light rather than lower quality.

This occurs in plants so that they can outcompete surrounding competitors that may be shading them.

Anthocyanin Production

Light can stimulate anthocyanin production, making fall leaves more colorful and fruits more red.

Photoperiodism

Photoperiodism..a plant’s response to daylength where darkness is the critical portion

Day neutral plants..plants that flower across a wide range of day lengths

Some day neutral plants flower more or less in response to day length, called quantitative long or short plants.

Long day plants..plants that flower when nights do not meet a critical length

Short day plants..plants that flower when nights are more than a certain critical length

Alternating day length plants..plants that need short days followed by long days or vice versa

Understanding photoperiodism allows plants to be produced in any hemisphere at any time.

Critical night length aries by species and by cultivar of a species.

Storage organ development can also depend on photoperiodism, such as in onion and garlic, which depend on a long day (short night)

Plants can be very sensitive to light when it comes to photoperiodism, with some being able to be reset by a flashlight.

Shade Tolerance

Many horticultural crops need full sun

Rapidly shifting an individual from shade to sun or vice versa can cause issues with scorching and mortality

Supplemental Lighting

A variety of supplemental lighting can be used to improve plant growth

High intensity discharge lamps are very expensive, but can last up to 24,000 hours, be used in windowless warehouses, and increased rose production by 240%

Fluorescent lamps are used in seed germination and tissue culture. They are less intense but can be used to lengthen the day

Incandescent lamps are too hot and have improper wavelengths, so they are primarily used to control the photoperiod

LED lights are expensive, but last longer, use less energy are harder to break, and can be put closer to plants than other light options.

Lecture 4: Temperature

Temperature is the most important factor in plant distribution. It also plays a major role in plant physiology, impacting growth, development, flowering, dormancy, yield, and color.

Hardy plants are less sensitive to temperature.

Tender plants cannot tolerate cold temperatures.

Classification

Many horticultural crops are divided into cool season, intermediated season, and warm season.

Most plants can survive from 0 to 50 degrees celsius, but 10 to 30 degrees celsius is optimal.

The USDA breaks the country into zones 1-11 based on annual minimum temperatures. Zones do not factor in maximum or mean temperatures.

Plants can be grown outside of their zones by using protection, placing them in sheltered areas, and burying them with soil and snow.

Soil Temperature

Soil temperature impacts seed germination, root growth, water uptake, and disease.

Plant roots stop growing when soil temperature is below 41 degrees Fahrenheit.

Sandy soils warm more quickly than clay soils due to differences in water content. Soil temperature is also impacted by air temperature, wind, and solar radiation.

Optimum soil temperature is 59-86 degreed Fahrenheit

Modifying Soil Temperature

Soil temperature can be modified by applying plastic mulch in light or dark colors to achieve the desired effect, altering soil moisture, heating irrigation water, or using heating pads.

Thermoperiodicity

Thermoperiodicity..When plants grow better with alternating day and night temperatures

In 1944 it was discovered that tomatoes grow much less when they are constantly at 80 degrees Fahrenheit than when the day was 80 degrees Fahrenheit and the night was 68 degrees Fahrenheit.

Thermoperiodicity is especially important to plant height

Recommendations regarding thermoperiodicity vary based on species, market, and sunny vs. cloudy.

Lilies, poinsettias, and chrysanthemums grow taller if night temperatures are constant and day temperatures are increased, but shorter if the night is increased and the day is constant.

The difference between night and day is DIFF, calculated by subtracting the night temperature from the day temperature.

Growing Degree Days

Growing degree days relate to development and reproduction of plants and insects. They are also known as heat units.

Growing degree days are used for organisms that cannot maintain their own temperature, where their development is predicted by temperature and time.

Growing degree days help people know when to scout for pests or market crops.

Minimum development threshold..minimum temperature at which growth occurs

Maximum development threshold..maximum temperature at which growth occurs

A growing degree day is 24 hours at 1 degree above the minimum development threshold

Biofix date..date at which you being calculations, including seedling emergency, calendar date, first trapping, etc.

Degree days= ((daily maximum temperature + daily minimum \n temperature)/2)-minimum threshold temperature

A plant needs a certain number of degree days to exist.

Dormancy

Buds of woody plants go to pre-dormancy in the summer, which is broken if the plant needs more growth. By winter the buds are dormant. If a plant is placed in a greenhouse after this, buds will not grow unless overcome by a chilling period.

There is a minimum number of hours that a temperature must be below a certain threshold for buds to break dormancy.

Chilling period varies by species and cultivar.

Endodormancy..imposed by internal blocks in seeds and buds, regulated by hormones and removed by winter chilling (rest)

Ectodormancy..plants refrain from growing until external conditions are satisfied (quiescence)

Both endodormancy and ectodormancy work together to prevent bud break during the wrong time of year.

We can overcome dormancy by calculating chilling hours and the heat units required for buds to break once chilling hours are reached.

Temperature Injury

Chilling Injury

Chilling injury can occur to tropical plants at temperatures as warm at 59 degrees Fahrenheit (non-freezing temperatures).

While tropical plants are susceptible to cold at any time, temperate plants have different tolerances depending on whether they are growing or dormant.

Two main freeze events can threaten plants that grow in temperate regions.

Advective freeze..mass of cold air moved in by strong winds often leading to temperatures below freezing for a full day or more.

It is difficult to protect plants from advective freezes as they are very windy and have long durations.

Radiational cooling..clear nights and calm winds that last a few hours.

Protection

There are multiple ways to protect from radiational cold events as they typically only last a few hours on either side of the sunrise.

Row covers..protection from radiational cooling that can offer 1-3 degrees C of protection. Woven materials protect more than paper or plastic

Torches..a method of protection from cooling events that uses open flames throughout plantings, used widely in European vineyards

Helicopters..can be used to protect crops from cooling by mixing the air

Irrigation may be used to protect plants. Overhead irrigation begins at a very specific time using low volume sprinklers. As the water freezes, it gives off heat that warms plant tissues. Irrigation must continue until the ice is melted. This method is only effective for short periods within a few degrees of freezing.

Other Forms of Winter Injury

Sunscald..damage of thin barked trees which occurs when temperatures are below freezing, sun hits the bark and raises the temperature, thawing the tissues, and freezing conditions return as soon as the sun is no longer on the tissues. The cells die and the bark splits.

Frost cracking..splitting of turns due to extremely cold temperatures

Summer Injury

Very high temperatures can kill plants

High head with direct sunlight can cause sunburn or sunscald.

Temperature Fluctuation Injury

Rapid changes in temperature can cause injury to plants, sometimes even including cold water falling on leaves.

Site Selection

Temperatures are important to consider when selecting a site, with many factors impacting it such as air, slope, altitude, bodies of water, and latitude.

Frost pockets..low areas where cold air settles

Cool air is more dense than warm air and thus will flow downhill. Fruit orchards are usually planted on slopes to avoid cool air.

Altitude..the elevation of the site

For every 300m increase in altitude, the air temperature can drop by 5 degrees celsius, and higher altitudes have higher thermoperiodicity.

Variables at particular latitudes make prime locations for fruit production.

Large bodies of water can be useful for crop production due to the temperature moderation provided by the heat capacity. Warm water in the fall protects from early frosts, cool water in spring prevents buds bursting before a cold snap, and summer and winter temperatures are much less extreme.

Lecture 5: Water

70% of the Earth’s surface is water and many ancient civilizations were built near water.

Water is important for plants so that they can perform photosynthesis. Requirements vary by crop, region, and development state. Herbaceous plants are 80-90% water by weight, woody plants are 50% water by weight, and tomatoes are 95% water.

200 to 1000 grams of water can be needed to produce 1 gram of dry matter.

Water has unique properties that make it even more useful for plants.

High specific heat stabilizes extreme temperatures
Water is a universal solvent, helping transport nutrients, fertilizers, sugars, and hormones
Surface tension
Turgor pressure keeps plants erect
Water in guard cells open stomata

Water in Air

Transpiration..loss of water from a plant as vapor. Loss occurs through stomatal openings

Evapotranspiration..evaporation loss of water from plants and soil influenced by humidity

Water in Soil

When soil is saturated, all pores are full of water moving along gravitational potential

When soil is not saturated, water moves by metric potential

Water enters plants through root tips.

Field capacity..when water is only held in small pores, reached when large pores are drained by gravity

Permanent wilting point..the point when water will not longer be able to be absorbed

Incipient wilting..occurs when plants temporarily wilt and then recover without additional water

Irrigation

Water penetration of soil is important in irrigation as runoff is not desired and standing water reduces oxygen to plants

Irrigation..supplemental meeting of water needs of a crop

There are many different ways to irrigate plants

Hand watering is simple and low cost, but has variable success and requires a lot of labor.
Furrow irrigation..irrigation where ditches are placed between crop rows and gates are open to release water
- Requires ground to have slope, not suitable for well draining soils, and does not wet foliage
Flood irrigation..irrigation that covers most of a field
- Most inefficient form of irrigation
High volume irrigation
- Overhead irrigation using sprinklers
- Circular pivot sprays in a circular pattern
- Lateral system walks through a field
- Common in fields as good airflow is needed if it is used in a greenhouse
- Wind can distort patterns
- Evaporation loss is high, equipment is expensive, and salt can build up in soils
Low volume irrigation
- Trickle or drip systems
- Conserves water, limits weeds, reduces disease issues, more uniform, and fertilizers can be added
- Clogging can be problematic, coyotes may destroy systems, and they are expensive
Subirrigation..applying water below the root zone
Floor flood
- Plants are on a floor or bench and flooded for 15 minutes at a time
- Efficient for water and fertilizer, low labor and cost
- Pathogens become problematic very quickly

Open irrigation system..water is not reused

Closed irrigation system..water is recycled repeatedly

Lecture 6: Nursery and Floriculture

Nursery Crops

Nursery crops mostly involve the sale of woody ornamental plants in one of the fastest growing segments of agriculture

In the USA there are both wholesale and retail nurseries

Wholesale nurseries have fewer crops on a larger scale and sell to other nurseries whereas retail nurseries often sell these plants.

Product mix..type of plants to be grown

Methods of Nursery Production

Container production and field production are used, but the trend is leaning towards container stock.

Less labor required
More control
High density of crop
Quicker recovery
More marketable

Container Nursery Production

Plants are grown in pots

Very valuable in the market
Pots need to last a long time
Ground needs to be level
Issues with root binding
Pots are expensive
Roots are not are protected in the winter
- Plants should be grouped together or border pots can be placed
- Alternatively, pots can be buried in the ground

Field Nursery Production

Fields need tilled before planting

Cover crops may be used to make soil more fertile
Plants must be spaced for maximum size because they cannot be moved
- Space for equipment must be considered as well
Plants may be sold “balled and burlapped” with a ball of soil dug up and wrapped or bare root, which risks transplant shock