Protected cultivation involves growing plants in a sheltered or enclosed environment, for the purpose of improving plant growth. Structures used to protect crops range from cloches and conservatories in home gardens through to highly sophisticated commercial greenhouses. The structure may provide partial enclosure, as in a shade-house, or full enclosure, as in a fully automated and heated glasshouse.
Many types of crops are grown under cover utilizing a particular climate, whereas, they can be produced in the open in another climate type. Whether a particular plant is treated as a “protected crop” or not will depend on when and where you grow it, and what you hope to achieve from the production of the crop.
The crops produced in a protected environment can be ornamental – for the home garden and nursery; for the cut flower industry; or food crops for commercial production. Types of plants include:
- Cut Flowers
- Container Plants
- Bedding Plants
- Over- wintering cold-tender species
- Display plants
There are 10 lessons in this course:
Structures For Protected Cropping
Cladding Materials And Their Properties
Relationship Between Production Techniques And Horticultural Practices
Horticultural Management In A Greenhouse: Pests And Diseases
Harvest & Post Harvest Technology
Each lesson culminates in an assignment which is submitted to the school, marked by the school's tutors and returned to you with any relevant suggestions, comments, and if necessary, extra reading.
Describe and Evaluate the type and shape of modern growing structures
Describe and evaluate environmental controls in protected cropping
Explain the nature of solar radiation, transmission properties of glass and its substitutes
Determine the water requirements of a crop; and methods of irrigation.
Relate horticultural principles to the production and harvesting of a range of crops.
Evaluate the factors involved in marketing protected crops
Evaluate the factors involved in marketing protected crops
Undertake risk assessment for a protected crop
What You Will Do
Identify the main types of growing structure
Relate use of structures to shape and type of construction
Identify the range of environmental factors controlled within a growing structure
Describe the use of the equipment used to measure and monitor these factors
Name and describe a range of types of environmental controls
Evaluate the use of IT facilities for environmental control
Describe the meaning of “daylight” and explain the role of sunlight and diffused light
Relate time of year to the quantity and quality of available light
Evaluate how the shape and orientation of a structure will affect light transmission
Assess the effectiveness of glass and cladding alternatives for light transmission
Describe the durability and insulation properties of glass and alternative materials
Select and describe appropriate systems of irrigation for plants grown in a situation
Select and describe appropriate systems of irrigation for container grown plants
Specify and evaluate systems for incorporating plant nutrients into the irrigation water
Explain the effects of environmental control on a range of plants
Relate the essential features necessary for successful plant establishment and development to their underlying scientific principles.
Describe the production of a range of crops
State the optimum stage of growth for harvesting a range of crops
Describe the harvesting systems for protected crops
Explain how shelf life can be affected by pre and post harvesting treatment of the crop
State the factors to be considered when marketing crops
Evaluate alternative marketing outlets
Relate packaging & presentation to marketing
Assess benefits to the grower and customer, of grading a crop before marketing
Determine elements of risk in the practical operations associated with protected plant production.
Identify safe working practices
How to Grow Plants Using Protected Environments
Even if you live outside of the tropics, you can grow tropical plants with the aid of structures that alter plant growing conditions. If you want to grow summer vegetables outside of summer; you can do that using similar protected environments.
Greenhouses, shadehouses, pergolas, conservatories, cold frames and cloaches are all useful structures for providing protection from weather extremes for tender plants. Such structures are commonly used to grow plants from the tropics and sub-tropics in cooler climate areas, or in areas where there is insufficient shade (e.g. growing rainforest understorey plants without the protection of upper storey plants).
For convenience in a cold climate, nothing beats a conservatory ‑ a glasshouse attached to the house, on the north or east side. A conservatory or greenhouses will allow you to:‑
Propagate new plants
Grow plants in cooler climatic conditions than what they would usually tolerate.
Protect plants which are cold or frost sensitive over winter
Protect plants from wind, hail and pests
Grow vegetables, cut flowers or berry fruits out of season, or faster than might be achieved outside.
This is great if you don't feel like walking to a greenhouse at the bottom of the garden in the rain. Conservatories are popular in colder climates like Europe, because even if it is cold and windy outside, as long as the sun is shining, it is pleasant to sit in a warm conservatory and dream of tropical islands. However, conservatories can be expensive to construct and a bay window or even a sunny window sill can be used to grow some parsley or other herbs. Conservatories can be covered with blinds or shadecloth in summer, (or grow beans on a trellis just in front of it) and in winter kept open to the house to warm it up.
Greenhouses or glasshouses provide permanent protected growing areas, and are usually sited independently of other buildings. When planning a greenhouse consider the following:
Is the site on a slope or flat. Too steep a site will make it impossible to build thegreenhouse unless it is stepped.
Is the site in sun or shade. A natural windbreak will also be useful, but take care to avoid shading the greenhouse.
Does the greenhouse require a concrete base?
What sort of soil is the greenhouse going to be built on. A sandy soil will give good drainage from any watering, but a clay soil will not. You may need to install a drainage system before construction.
- If you decide to build a greenhouse at the bottom of the garden it is a good idea to at least partially obscure it with climbers on a trellis, or behind some shrubs. A greenhouse can tend to dominate, and ruin an otherwise carefully designed garden. Care should be taken with your choice of screen, as a heavily shaded glasshouse will not be suitable for growing plants.
Which way should the greenhouse be sited, either north ‑ south or east west? A greenhouse that is sited with it's ridge running east to west is best, but this may be a fact which is governed by the space that you have available.
If you are planning to automate some of the functions of your greenhouse, or provide electrical heating, a power supply will be essential. A greenhouse will be a damp place, so it is important that all electrical connections are made by a registered electrician.
- Metal Aluminium frames are popular because they resist rusting. Galvanised iron or steel are also used, though over time corrosion can become a problem. Glass works well with metal, however PVC film and other plastics can deteriorate if in direct contact with metal (e.g: metal will get very hot in summer sections of PVC film touching it will crack or tear much sooner than parts not in contact).
- Timber Timber does not heat up like metal, however it will rot, particularly in the humid environment of a greenhouse. Some treated timbers will last for many years, but it is important to check that the materials used in treating the wood are non‑toxic to plants. Pests such as mealy bug may also breed in timber.
- Greenhouses are commonly covered with
glass, polythene or polyflute. Other alternatives include polycarbonate
sheeting, fibreglass and others. All have advantages and disadvantages:
- Glass ‑ very long lasting, strong, expensive. Excellent light transmission and holds heat in well. Looks good.
- Polyflute, corflute ‑ medium life span, quite strong, moderately expensive. Poor light transmission, good insulation. Tends to collect dust. Easy to build with.
- Polycarbonate ‑ Long lasting, very strong, expensive. Available in clear or smoky grey sheets, corrugated or 'Grecca' style. Excellent light transmission, flexible and easy to work with. Collects dust. Looks good.
- Fibreglass ‑ tends to collect dust, and become brittle and yellow with age, generally not as good as alternatives. Green corrugated sheets are no good for growing plants under.
- Polythene ‑ short life span, changed every three to five years in most cases. Relatively cheap in the short term. Inclined to form condensation on the inside which causes dripping (on plants and you), and leads to heat loss. Not as well insulated as glass, occasionally used as a double cover to improve insulation, but some light is lost. Good light transmission but some brands become yellow with age. Strength and durability and brittleness depends on brand, with some incorporating woven thread for strength. Can flap noisily in the wind and is not particularly good to look at. Polyhouses are better sealed than glasshouses and tend to get hotter than glasshouses, and more humid, which makes them less comfortable for some plants and people.
What to Grow in Conservatories and Greenhouses?
This is of course largely a matter of personal preference and the range of plants that you can grow will be only controlled by the limitations of your conservatory or greenhouse. Temperature will be a deciding factor as to the choice of your plants, and you need to decide on what temperature you are going to have as a constant in the greenhouse.
If you want to control the temperature in your building, you can do this in a number of ways.
- The sun will warm the structure during the day, and the degree of warming will depend upon the time of the year, time of day and weather conditions that day.
- Heaters can be used to add to the heat in the house. The heater must have the ability to replace heat at the same rate at which it is being lost to the outside.
- Vents and doors can be opened to let cool air into the house, or closed to stop warm air from escaping.
- Shade cloth can be drawn over the house to stop the warm sun penetrating it. Whitewash can also be applied to the glass to give the same effect. The whitewash used is usually one that lasts the summer but will wash off with weathering to allow the penetration of warming light in the winter.
- Fans can be used to lower temperature.
- Watering or mist systems will also lower temperature.
If you intend to grow pot plants in a greenhouse, you probably need some benches. Benches enable you to raise plants off of the greenhouse floor, keeping them away from disease and often in better light. A tiered system of benches usually provides more useable space than if you were to only use the floor. Benches can be made out of metal, wood or plastic, and are usually either slatted or solid in construction. The surface of a bench should drain freely. Wooden benches if not treated with preservative can rot, and may become infested with pests such as ants or mealy bug. Capillary matting (ie. a continually moist, absorbent material, sold by some greenhouse companies) will help reduce the need for watering if used on a bench, to sit pots on.
Pergolas are structures built to provide shade and shelter. They can produce a cool humid environment preferred by ferns and many tropical tree seedlings; or can be covered with water proof material to prevent rainfall thereby reducing humidity, increasing heat and producing a more arid situation.
Pergolas usually consist of a roof supported by posts and/or walls of an adjacent building, with the sides open or enclosed. The roof is commonly made from beams covered by something to filter the sunlight while still allowing rain to penetrate. Pergolas are commonly constructed over a path, patio or verandah so as to increase the useable area of the land for living space or plant growing. They may be attached to or between buildings. In the southern hemisphere, pergolas are normally attached to the north side of the house to provide shade in the heat of the day. In warmer climates a pergola can also be very useful on the east and west sides of your house where the morning and afternoon sun can be more of a problem than the high midday sun.
There are three parts to a pergola:
1. The posts (uprights)
2. Roofing framework
3. Covering material (not always used).
Posts and roofing framework are usually made from timber. Metal is sometimes used. In most situations, a height of 2.5 metres is ideal for pergolas.
The covering material is very important as it will effect the amount of light, or shade, that the plants will receive. A solid cover creates a more shaded, cooler area, but restricts rainwater moving through. Plants under a pergola may need more watering.
The main choices in coverings are:
a. Growing Plants
- The combination of foliage, flower, scent and colour provide a sense of continual change and freshness.
- Regular pruning may be necessary to remove growth hanging too low, or spreading beyond the pergola.
- Avoid plants that may damage an attached building (eg. Ivy) or block guttering.
- Deciduous climbers will let light through during winter (when bare of leaves), but provide coolness and shade in summer.
b. Brush (cut foliage for plants)
- Brush can be purchased in bundles or slabs, or cut yourself (do not cut it from the bush though) from plants like Melaleuca and tea tree.
- It can in some cases carry disease and may be readily flammable if lit.
- Soft wooded plants are rarely any good as brush.
- Water moves in an irregular way through brush, creating heavy dripping in some places.
- Shadecloth comes in a variety of degrees of shade.
- Lasts for a very long time.
- Needs to be well supported by beams and slats, or it will sag, forming low spots which collect leaves and other rubbish.
d. Timber slats
- Timber slats or battens give an optimum cooling effect if run in a north-south direction.
- All timber needs to be treated to extend life.
e. PVC or Fibreglass sheet
- Sheeting must have a slope to move rainwater. It is normal to slope the roof away from buildings or pathways, to keep those areas free of water.
- A collection system or guttering may be used at the bottom of the roof, and take it to a drain.
Covering material of shadehouses has been primarily with the use of banboo or wooden slats, or shadecloth.
Shadecloth colours are now available in:
- Green ‑ although it may look good in the garden, it is the least desirable colour as the plants do not photosynthesis effectively under this colour cloth.
- Black ‑ very popular and is perhaps the colour which is least noticeable.
- Brown ‑ fits in well with rustic and colonial style homes and with native bush gardens.
- Sandstone ‑ may be in keeping with the colour of the bricks or roof tiles of a house.
- Pale blue and white ‑ go well with white houses and swimming pools. White shadecloth is good for growing plants, as they are protected but still grow in bright conditions, as the light is reflected and dispersed as it passes through.
In warmer climates, darker coloured shade cloth will have more of a cooling affect than the lighter colours.
Shadecloth is available in a range of shade strengths, ie. 50% and 70%. Stronger cloth is better in warm hot areas for the growing of more tender plants. 50% shadecloth is good for most other plants especially orchids and other flowering plants.
Shade cloth can also be used as a windbreak substance.
Pergolas and shadehouses are ideal for growing ferns, azaleas and orchids. They can also be used to grow rainforest plants like gingers, monstera, philodendrons and cunjevois; or frost/heat sensitive plants such as fuchsias, impatiens and begonias.
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