Plant needs, Horticultural plants
The word horticulture comes from Latin and refers to the cultivation of gardens. There are three main branches of the science of growing plants: forestry, agronomy, and horticulture. Forestry is concerned with the cultivation of stands of trees for their commercial and ecological uses. Agronomy involves the large-scale cultivation of crops, such as wheat, cotton, fruits, and vegetables. Horticulture involves growing plants for their aesthetic value (e.g., in floriculture; the cultivation of flowers), or on a very local scale as food (as in a home garden).
In addition to home gardening, horticulturists are involved in the landscaping and maintenance of public gardens, parks, golf courses, and playing fields. Seed growers, plant growers, and nurseries are the major suppliers of plants and supplies for use in horticulture. Among the important specialists working in horticulture are plant physiologists, who work on the nutritional needs of plants, and plant pathologists, who are engaged in protecting plants from diseases and insect damage.
For the amateur home gardener, the rewards of horticulture are both recreational and emotional. Gardening is one of the most popular pastimes for many people—for those living in suburbs, as well as city dwellers who plant window boxes, grow house plants, or develop a garden in a vacant lot.
Whether plants are being grown on a large scale for commercial purposes or for the pleasures of having a garden, they have fundamental needs that include a suitable regime of water, soil, and climate.
The climatic factors that have the greatest effects on plant growth are temperature, precipitation, humidity, light, and wind. In deciding what plant species can be grown in a particular location, the horticulturist must consider whether the seasonal ranges of temperature can be tolerated. Many plants will die if exposed to temperatures as low at 28°F (-2.2°C), although others are frost hardy and can be grown in places much colder than this. While some plants die from frost, others may only die back and then recover when warmer weather returns. Conversely, many plants need exposure to seasonally cold temperatures, as occurs during the wintertime.
Another climatic factor affecting plants is precipitation. The amount of moisture that plants require varies greatly. Desert plants can survive on little water, and may perish if over-watered. Other plants need continuously moist growing conditions. Plants of some coastal habitats receive benefits from fog and moist air blowing in from over the water. However, too much dew can damage some plants, by predisposing them to fungal diseases. In many regions, trees overburdened by heavy, freezing rain are subject to broken branches.
The amount of sunlight plants receive also affects their growth. The intensity and duration of light controls the growth and flowering of plants. Insufficient light results in the rate of photosynthesis being insufficient to allow the plant to grow and flower. Wind is another important factor, which can cause damage by increasing the rate of water loss, and if extreme by breaking off plant parts. Strong wind blowing from oceans can deposit harmful salts on sensitive plants.
All these climatic factors must be considered by horticulturists when planning a garden or landscaping project. These factors determine the possible selection of plants for a particular ecological context.
All types of soils need management for optimum plant growth. Some soils are rich with clay, while others are sandy or rocky. Clay soils are heavy and tend to drain water poorly, which may cause plant roots to become waterlogged and oxygen-starved. Sandy or rocky soils, on the other hand, drain water rapidly and may have to be irrigated to grow plants well. Usually, the preferable garden soil is loamy, meaning it consists of a balanced mixture of clay, sand, and organic matter. Organic matter in soil is important because it helps develop larger pore spaces and allows water and air to penetrate. This helps roots to grow well and absorb nutrients for use by the plant.
Other important soil factors include the acidity or alkalinity of the soil, the presence of beneficial or harmful microscopic organisms, and the composition and structure of the soil layers (topsoil and subsoil). The addition of mineral nutrients and organic matter to soil being prepared for planting is a common practice in horticulture. This may include the addition of fertilizers that meet the nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, and trace-element needs of the plants.
Thousands of plant species are available for use in horticulture. Many of these have been domesticated, selectively bred, and hybridized from the original, wild, parent stocks, and are now available in large numbers of cultivated varieties (or cultivars). Consider, for example, the numerous varieties of roses, tulips, geraniums and many other common horticultural plants that can be obtained from commercial outlets.
In most places, almost all of the horticultural plants that are widely grown in parks and gardens are not indigenous to the region (that is, their natural habitats are far away, usually on another continent). This widespread cultivation of non-native plants has resulted in some important ecological problems, caused when the horticultural species "escape" to the wild and displace native plants. Because of this kind of severe ecological damage, many environmentalists are advocating the cultivation of native species of plants in horticulture. If this sensible "naturalization" is practiced, there are fewer problems with invasive aliens, and much better habitat is provided for native species of animals. This means that horticulture can achieve important ecological benefits, in addition to the aesthetic ones.
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