Specification of structures Flashcards
Examples
Greenhouses
Cold frames
Polythene tunnels
Conservatories
Environment of protected structures
Control of following factors:
Growing medium - easier to specify, less prone to soil-borne pests
control of soil temperature - basal heat
Aerial environment - humidity - damping down - misting
air temperature - heating
gas exchange (carbon dioxide enrichment)
ventilation - air movement with use of side and roof vents, or fan ventilation
shade - paint or netting
lighting (supplementary)
Irrigation - overhead, capillary matting
Uses of protected structures
Growing tender/exotic plants
Helping to harden off plants
Providing controlled environments for demanding plants eg alpines
Temporary decorative display of plants at their peak
Overwintering
Propagation
Production of high quality cut flowers
Production of exotic fruit and veg
Benefits of protected structures
Extending growing season for food production
Improving quality of crops/flowers and yield
Enable application of biological controls (Encarsia formosa - check spelling)
All year round production of crops eg carnations and lettuces
Less dependent on weather
In GH auto control of temp, irrigation, light, CO2 levels, feeding, humidity
Use of mist benches and heated cases aids propagation
Conditions can be varied for different crops
Limitations
If not managed well, the greenhouse effect can make environment hostile for plants (too humid, too dry or too hot, and in winter plants may use more energy than they capture by photosynthesis)
Specific pests/diseases thrive in a protected environment
Costs of building, equipping and maintaining structures
Cost of heating/lighting
Cloches - features
Small, temporary and moveable covers
Traditionally glass but plastic is also popular (safer and easier to handle)
Benefits: cheap form of protection from wind and rain and temperature and humidity is slightly higher
Limitations: limited options to control growing environment
Uses: provide protection for early outdoor crops
Can be used to warm soil prior to sowing or planting
Advances/extends growing season for crops for two to three weeks
Strip cropping where cloches are moved to and fro between adjacent plots to cover thee or four different crops at critical growth stages
Tunnel cloches
Long, low, protection
Made from eg polythene sheets or horticultural fleece stretched over wire hoops or sheets of corrugated plastic held in place by pegs.
Can be quite elaborate and include irrigation systems and adjustable ventilation
Benefits: cheap form of protection from wind and rain and temperature and humidity is higher
Limitations: limited options to control growing environment
Uses: provide protection for early outdoor crops
Can be used to warm soil prior to sowing or planting
Advances/extends growing season for crops for two to three weeks
Strip cropping where cloches are moved to and fro between adjacent plots to cover thee or four different crops at critical growth stages
Cold frames
Low boxes in which plants can be propagated and grown. They can be covered with lights or left open. Optimum size 1.2x0.6m
Should be sited in a shaded, frost free area
Compost or improved soil should be added in the frame
Uses: may be used for cuttings, or seed sowing, or for pots or trays of propagation material, low growing crops, plants to be over wintered or hardened off before planting out
Polythene tunnel
A large walk-in structure. Increasingly favoured over glasshouses
Benefits: cheaper to purchase/erect. Will keep out to worst of the winter cold and protect against strong wind and heavy rain Irrigation and heating can be installed.
Limitations: not aesthetically please, poorly ventilated and plastic ‘skins’ need replacing every 3 or 3 years.
Uses: propagation and growing on in nursery industry and for the commercial production of vegetables and cut flowers
Glasshouses
These range from functional to ornamental and may be free standing or lean-to
Light transmission: most efficient at 90 degree (90% of light transmitted, 10% reflected)
A dome shape maximises transmission as some part of the dome is a right angle to the sun whatever the season or time of day. A circular floor plan and sloping sides makes this impractical. A Mansard design (pictured) is a compromise, is Dutch light
Benefits: aesthetic, a range of options to control environment, eg light levels, temp light and day, irrigation, ventilation, gas concentrations
Limitations: high costs of building and equipping GH, high cost of heating and lighting, overheating and drying out due to greenhouse effects in summer
Uses: vegetable and cut flower production
Overwintering of plants, propagation of plants, growing of tender plants, growth and display of specialist plants eg alpines which require specific conditions
Uses
Glasshouse - diagram
Polytunnel - diagram
Cladding Materials - glass
Benefits: best for light transmission
easy to clean
does not deteriorate with age
Limitations: heavy
fragile
can be dangerous
more expensive
Cladding Materials - polycarbonate
Benefits: Good insulation (double skinned with air pockets)
Does not shatter (safer)
Easier to cut than glass
Limitations: light transmission in 75%
more expensive than glass
Long lived
Cladding Materials - polyethylene
(polytunnels, tunnel cloches, mini glass houses)
Benefits: relatively inexpensive
good light transmission when new (similar to glass)
lightweight requiring less frame and more light transmission
Limitations: deteriorates in the sun and becomes cloudy
can rip and develops holes
replacement every 3-4 years
