Horticulture

Horticulture is the science and art of growing fruits, vegetables, flowers, or ornamental plants. Horticulture is commonly associated with the more professional and technical aspects of plant cultivation on a smaller and more controlled scale than agronomy. There are various divisions of horticulture because plants are grown for a variety of purposes.^[1] These divisions include, but are not limited to: propagation, arboriculture, landscaping, floriculture and turf maintenance. For each of these, there are various professions, aspects, tools used and associated challenges; Each requiring highly specialized skills and knowledge of the horticulturist.

Typically, horticulture is characterized as the ornamental, small-scale/non-industrial cultivation of plants; horticulture is distinct from gardening by its emphasis on scientific methods, plant breeding, and technical cultivation practices, while gardening, even at a professional level, tends to focus more on the aesthetic care and maintenance of plants in gardens or landscapes. However, there are aspects of horticulture that are industrialized/commercial such as greenhouse production or CEA.

Horticulture began with the domestication of plants around 10,000-20,000 years ago.^[2][3] At first, only plants for sustenance were grown and maintained, but eventually as humanity became increasingly sedentary, plants were grown for their ornamental value. Horticulture emerged as a distinct field from agriculture when humans sought to cultivate plants for pleasure on a smaller scale rather than for mere sustenance.

Emerging technologies are moving the industry forward, especially in the way of altering plants to be more adverse to parasites, disease and drought. Modifying technologies such as Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR/Cas9), are also improving the nutrition, taste and yield of crops.

There are many horticultural organizations and societies found around the world, that are formed by horticulturists and those within the industry. These include the Royal Horticultural Society, the International Society for Horticultural Science,^[4] and the American Society of Horticultural Science.^[5]

There are divisions and sub-divisions within horticulture, this is because plants are grown for many different reasons. Some of the divisions in horticulture include:

• gardening
• plant production and propagation
• arboriculture
• landscaping
• floriculture
• garden design and maintenance
• turf maintenance
• plant conservation and landscape restoration.^[6][7][8]

It includes the cultivation of all plants including, but not limited to: ornamental trees/shrubs/plants, fruits, vegetables, flowers, turf, nuts, seeds, herbs and other medicinal/edible plants. This cultivation may occur in garden spaces, nurseries, greenhouses, vineyards, orchards, parks, recreation areas, etc.

Horticulturists, are those who study and practice the cultivation of plant material professionally. There are many different types of horticulturists with different job-titles, including: gardener, grower, farmer, arborist, floriculturist, landscaper, agronomist, designer, landscape architect, lawn-care specialist, nursery manager, botanical garden curator, horticulture therapist, and much more.^[9] They may be hired by a variety of companies/institutions including, but not limited to: botanical gardens, private/public gardens, parks, cemeteries, greenhouses, golf courses, vineyards, estates, landscaping companies, nurseries, educational institutions, etc. They may also be self-employed.

Horticulture began with the domestication of plants 10,000-20,000 years ago, and has since, been deeply integrated into humanity's history.^[2][3] The domestication of plants occurred independently within various civilizations across the globe. The history of horticulture overlaps with the history of agriculture and history of botany, as all three originated with the domestication of various plants for food.^[3] In Europe, agriculture and horticulture diverged at some point during the Middle Ages.^[10]

Early practices in horticulture include a number of various ways that people managed the land (using an assortment of tools), with a variety of methods and types of plants cultivated for a number of uses. Methods, tools and plants grown, have always depended on the culture and climate.

There are a number of traditional horticultural practices that we know of today: such as the Indigenous peoples of pre-colonized North America using biochar to enhance soil productivity by smoldering plant waste^[11] - European settlers called this soil Terra Preta de Indio.^[12] In North America, Indigenous people grew maize, squash, and sunflower - among other crops. Mesoamerican cultures focused on the cultivating of crops on a small scale, such as the milpa or maize field, around their dwellings or in specialized plots which were visited occasionally during migrations from one area to the next.^[13] In Central America, the Maya involved augmentation of the forest with useful trees such as papaya, avocado, cacao, ceiba and sapodilla. In the fields, multiple crops such as beans, squash, pumpkins and chili peppers were grown. The first horticulturists in many cultures, were mainly or exclusively women.^[14]

In addition to the medicinal and nutritional values that plants hold, plants have also been grown for their beauty, and to impress and demonstrate power, knowledge, status and even wealth of those in-control of the cultivated plant material. This symbolic power that plants hold has existed even before the beginnings of their cultivation.^[15]

There is evidence that various gardens maintained by the Aztecs were sacred, as they grew plants that held religious value. Plants were grown for their metaphorical relation to Gods and Goddesses.^[10] Flowers held symbolic power in religious rites, as they were offered to the Gods, as well as were given in ceremonies to leaders to demonstrate their connection to the Gods.^[10]

Plant propagation in horticulture is the process in which the multiplication of a species is performed, increasing the number of individual plants. Propagation involves both sexual and asexual methods.^[16] In sexual propagation seeds are used, while asexual propagation involves the division of plants, separation of tubers, corms, and bulbs - by use of techniques such as cutting, layering, grafting.^[17]

When selecting plants to cultivate, a horticulturist may consider aspects based on the plants intended use and can include plant morphology, rarity, and utility.^[18] When selecting plants for the landscape, there are necessary observations of the location that must be made first. Considerations as to soil-type, temperature/climate, light, moisture, and pre-existing plants are made. These evaluations of the given environment are taken into consideration when selecting plant material for the location. Plant selection may be for annual displays, or they may be for more permanent plantings. Characteristics of the plant such as mature height/size, colour, growth habit, ornamental value, flowering time and invasive potential are what finalizes the plant selection process.

Environmental factors that effect plant development include: temperature, light, water, pH, nutrient availability, weather events (rain, snow, sleet, hail and freezing rain, dew, wind and frost) humidity, elevation, terrain, and micro-climate effects.^[1] In horticulture, these environmental variables may be avoided, controlled or manipulated in an indoor growing environment.

Plants require specific temperatures to grow and develop properly. Temperature control can be done through a variety of methods. Covering plants with plastic in the form of cones - called hot caps, or tunnels, can help to manipulate the surrounding temperature. Mulching is also an effective method to protect outdoor plants from frost during the wintertime. Inside, other frost prevention methods include the use of wind machines, heaters, and sprinklers.^[19]

Plants have evolved to require different amounts of light, and lengths of daytime; their growth and development is determined by the amount of light/light intensity that they receive. Control of this may be achieved artificially through the use of fluorescent lights in an indoor setting. Manipulating the amount of light also controls flowering. Lengthening the day encourages the flowering of long-day plants and discourages the flowering of short-day plants.^[19]

Water management methods involve employing irrigation/drainage systems, and controlling soil moisture to the needs of the species. Methods of irrigation include surface irrigation, sprinkler irrigation, sub-irrigation, and trickle irrigation. Volume of water, pressure, and frequency are changed to optimize the growing environment. On a small scale watering can be done manually.^[19]

The choice of growing media and components to the media help support plant life. Within a greenhouse environment, growers may choose to grow their plants in an aquaponic system where there is no soil used. Growers within a greenhouse setting will often opt for a soilless mix which does not include any actual components of naturally occurring soil. These mixes offer advantages such as water absorption, sterility, and are generally very available within the industry.

Soil management methods are broad, but includes the use of fertilizers, planned crop rotation to prevent the degradation of soils that are seen in monocultures, applying fertilizers, and soil analysis.^[19]

Abiotic factors such as weather, light and temperature are all things that can be manipulated with enclosed environments such as cold frames, greenhouses, conservatories, poly houses and shade houses. Materials that are used in the construction of these buildings are chosen based on the climate, purpose and budget.

Cold frames provide an enclosed environment, they are built close to the ground and with a top made of glass or plastic. The glass or plastic allows sunlight into the frame during the day and prevents heat loss that would have been lost as long-wave radiation at night. This allows plants to start to be grown before the growing season starts. Greenhouses/conservatories are similar in function, but are larger in construction and heated with an external energy source. They can be built out of glass, although they are now primarily made from plastic sheets. More expensive and modern greenhouses can include temperature control through shade and light control or air-conditioning as well as automatic watering. Shade houses provide shading to limit water loss by evapotranspiration.^[19]

Commercial horticulture is required to support a rapidly growing population with demands for its products.^[20] Due to global climate change, extremes in temperatures, strength of precipitation events, flood frequency, and drought length and frequency are increasing. Together with other abiotic stressors such salinity, heavy metal toxicity, UV damage, and air pollution, stressful environments are created for crop production. This is extrapolated as evapotranspiration is increased, soils are degraded of their nutrients, and oxygen levels are depleted, resulting in up to a 70% loss in crop yield.

Living organisms such as bacteria, viruses, fungi, parasites, insects, weeds and native plants are sources of biotics stresses and can deprive the host of its nutrients.^[21] Plants respond to these stresses using defence mechanisms such as morphological and structural barriers, chemical compounds, proteins, enzymes and hormones.^[22] The impact of biotic stresses can be prevented using practices such as incorporate tilling, spraying or Integrated Pest Management (IPM).^[23]

Care is required to reduce damages and losses to horticultural crops during harvest.^[24] Compression forces occur during harvesting, and horticultural goods can be hit in a series of impacts during transport and packhouse operations. Different techniques are used to minimize mechanical injuries and wounding to plants such as:^[25]

• Manual harvesting: This is the process of harvesting horticultural crops by hand. Fruits, such as apples, pears and peaches, can be harvested by clippers
• Sanitation: Harvest bags, crates, clippers and other equipment must be cleaned prior to harvest.^[25]

Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR/Cas9) has recently gained recognition as a highly efficient, simplified, precise, and low cost method of altering the genomes of species.^[26] Since 2013, CRISPR has been used to enhance a variety of species of grains, fruits, and vegetables. Crops are modified to increase their resistance to biotic and abiotic stressors such as parasites, disease, and drought as well as increase yield, nutrition, and flavour.^[27] Additionally, CRISPR has been used to edit undesirable traits, for example, reducing the browning and production of toxic and bitter substances of potatoes. CRISPR has also been employed to solve issues of low pollination rates and low fruit yield common in greenhouses. As compared to Genetically Modified Organisms (GMO), CRISPR does not add any alien DNA to the plant's genes.^[28]

There are various organizations worldwide that focus on promoting and encouraging research and education in all branches of horticultural science; such organizations include the International Society for Horticultural Science^[4] and the American Society of Horticultural Science.^[5]

In the United Kingdom, there are two main horticulture societies. The Ancient Society of York Florists is the oldest horticultural society in the world and was founded in 1768; this organization continues to host four horticultural shows annually in York, England.^[29] Additionally, The Royal Horticultural Society, established in 1804, is a charity in United Kingdom that leads on the encouragement and improvement of the science, art, and practice of horticulture in all its branches.^[30] The organization shares the knowledge of horticulture through its community, learning programs, and world-class gardens and shows.^{[citation needed]}

The Chartered Institute of Horticulture (CIH) is the Chartered professional body for horticulturists and horticultural scientists representing all sectors of the horticultural industry across Great Britain, Ireland and overseas.  It is the only horticultural professional body where its top professionals can achieve Chartered status and become a Chartered Horticulturist. The Australian Institute of Horticulture and Australian Society of Horticultural Science was established in 1990 as a professional society to promote and enhance Australian horticultural science and industry.^[31] Finally, the New Zealand Horticulture Institute is another known horticultural organization.^[32]

In India, the Horticultural Society of India (now Indian Academy of Horticultural Sciences) is the oldest society which was established in 1941 at Lyallpur, Punjab (now in Pakistan) but was later shifted to Delhi in 1949.^[33] The other notable organization in operation since 2005 is the Society for Promotion of Horticulture based at Bengaluru.^[34] Both these societies publish scholarly journals – Indian Journal of Horticulture and Journal of Horticultural Sciences for the advancement of horticultural sciences.^{[citation needed]} Horticulture in the Indian state of Kerala is spearheaded by Kerala State Horticulture Mission.

The National Junior Horticultural Association (NJHA) was established in 1934 and was the first organization in the world dedicated solely to youth and horticulture. NJHA programs are designed to help young people obtain a basic understanding of horticulture and develop skills in this ever-expanding art and science.^[35]

The Global Horticulture Initiative (GlobalHort) fosters partnerships and collective action among different stakeholders in horticulture. This organization has a special focus on horticulture for development (H4D), which involves using horticulture to reduce poverty and improve nutrition worldwide. GlobalHort is organized in a consortium of national and international organizations which collaborate in research, training, and technology-generating activities designed to meet mutually-agreed-upon objectives. GlobalHort is a non-profit organization registered in Belgium.^[36]

• C.R. Adams, Principles of Horticulture Butterworth-Heinemann; 5th edition (11 Aug 2008), ISBN 0-7506-8694-4.