Protected structures

Question 1

Describe a greenhouse/glasshouse

Answer 1

A structure with a frame constructed from steel, aluminium or wood, usually clad in glass or plastic.

Many different styles and intended uses.

Choice of style will depend on intended use and location.

Can be heated or unheated, and can include top and bottom vents.

Question 2

Describe horticultural use for a greenhouse/glasshouse

Answer 2

Propagation (inc. cuttings and seeds)

Crop production

Overwintering of tender perennials and houseplants

Decorative display of specialist plant collections

Question 3

Describe a cold frame

Answer 3

Low structure consisting of a wooden, aluminium or brick frame

Cladding panes on top, known as lights, made from glass or plastic

Lights can be opened using hinges, or slid upwards.

Question 4

Describe horticultural use of a cold frame

Answer 4

Sowing seeds

Hardening off seedlings

Overwintering vulnerable plants

Weaning cuttings

Protecting young plants

Forcing bulbs into early flower

Giving crops extra protection early in the season.

Question 5

Describe a polythene tunnel

Answer 5

Large tunnels made of polythene sheeting stretched over a series of arc-shaped frames (usually made from steel or aluminium

Doors at the ends but no vents

Inexpensive and flexible alternative to a greenhouse

Question 6

Describe horticultural use of a polythene tunnel

Answer 6

Overwintering half-hardy and sensitive plants

Hardening off young plants.

Plants are planted into the soil or laid out in pots.

Provide shelter from rain and wind and maintain a higher temperature and RH than outdoors, but are not usually heated like greenhouses

Question 7

Describe a cloche

Answer 7

Low structure designed to protect individual plants or rows of plants.

Different shapes and sizes.

In longer cloches with frames, the frames are made of plastic or aluminium and the cladding is glass or plastic.

Individual cloches may be made of plastic or glass and can be improvised from plastic bottles with the bottoms cut off.

Question 8

Describe horticultural use of a cloche

Answer 8

Protecting a wide range of plants from rain and wind

Providing a higher temperature and humidity than if they were unprotected.

Often used to give seedlings and young plants a head start in spring

Sheltering vulnerable plants over winter and for low-growing crops like Lactuca sativa (lettuce).

Stopping pests like birds and rabbits from getting to crops.

Question 9

Describe a conservatory

Answer 9

A structure built onto to a house and is like an extension or extra room.

In effect, an ornamental greenhouse.

Conservatories may or may not be used primarily for plants and are often furnished.

Framework may be wood, plastic or metal, sometimes with a brick or concrete base

Cladding is usually toughened glass, often double-glazed.

Range of styles from Victorian to modern - important that the design matches or complements that of the house.

Question 10

Describe horticultural use of a conservatory

Answer 10

Sheltered environment that can be environmentally controlled though, depending on its main uses, control may not be as complete as in a greenhouse.

As the construction is more substantial than greenhouses, less light enters them.

Used for display of plants rather than for crops or propagation

Suitable for half-hardy, subtropical, and even tropical foliage and flowering plants.

Question 11

Environmental differences between protected environments (PE) and outdoors - TEMPERATURE

Answer 11

Air temp in a PE is more important than the soil temp.
Air temp in PE is easily controlled: heated to appropriate levels for propagation; no huge fluctuations; ventilation for cooling.

Air temp outdoors is only controllable in terms of careful situation of plants (e.g. shelter, frost pockets, shading)

Question 12

Environmental differences between protected environments and outdoors - HUMIDITY

Answer 12

RH outdoors does not need controlling and will usually be at the optimum range.

RH in a PE needs regulating through air movement and ventilation, and damping down when necessary.

Question 13

Environmental differences between protected environments and outdoors - LIGHT

Answer 13

Outdoors plants will get the correct amount and quality of light if situated in the correct place.

In a PE, the light may need supplementing and/or replacing if needed, depending on day length and situation of protected structure.

Question 14

Environmental differences between protected environments and outdoors - GAS CONCENTRATION

Answer 14

Outdoors, the concentration of atmospheric gases is always right for plants.

In a PE, CO2 can become a limiting factor for photosynthesis, and so CO2 enrichment may be necessary. Ventilation is important for this also.

Question 15

Environmental differences between protected environments and outdoors - AIR MOVEMENT

Answer 15

Outdoors there is no way of controlling air movement, but shelter can be provided if necessary.

In a PE, air movement is important to regulate RH and allow the right concentration of gases; and to minimise disease transmission.

Question 16

Environmental differences between protected environments and outdoors - IRRIGATION REQUIREMENTS

Answer 16

Outdoors, depending on the climate, plants will receive rain and extra irrigation from humans.

In a PE, plants are 100% reliable on human intervention for their watering. Overhead watering and sub-irrigation can be used for crops grown in containers and in the border soil.

Question 17

Benefits of using protected structures for growing plants, compared with growing the same plants outdoors - with example!

Answer 17

Eg. Solanum Lycopersicum

In a PE, it will benefit from:
Being kept at the correct constant temp;
Being kept in the optimum RH
Receiving the right amount of light
Being able to control CO2 concentration
Ventilating and air movement as needed, to avoid risk of disease
Being able to set up a regular watering regime.

Means:

Higher yields
Better quality
Longer season of fruiting and ripening
Able to grow greater range of cultivars

Question 18

Limitations of using protected structures for growing plants, compared with growing same plants outdoors - plus example!

Answer 18

Eg. Solanum lycopersicum.

• Relative costs to set up the protected structure;
• More effort required with maintenance (irrigation, ventilation, damping down etc.);
• P&D problems are different indoors than outdoors;

Question 19

Effects of environmental factors on plants in a protected environment - with named plant(s) and horticultural situation(s):

Answer 19

Named plant: Solanum Lycopersicum.

Temperature:
As tomatoes do best between 21-24C, growing under cover can increase the quality of fruit and give a bigger yield, but higher temperatures also increase P&D infestations.

Humidity:
Lowering the humidity will make infection from fungal diseases (eg Tomato leaf mould) less likely. Raising the humidity will help control Red spider mite.

Light:
Lack of light would result in tomato seedlings becoming leggy and weak (etiolation), making them prone to pest infestation (usually whitefly);

Concentration of atmospheric gases:
Lack of Co2 and O2 in the environment will affect the plant’s ability to both photosynthesise and respire, hence to grow, and both too much and too little humidity in the environment will impact the plants’ ability to take up water through transpiration.

Air movement:
Too little air movement can encourage Tomato leaf mould to develop rapidly, causing significant yield loss (rarely seen on outdoor crops), so ample ventilation is important.

Irrigation requirements:
Water regularly, not sporadically and never allow the soil to dry out (can result in Blossom end rot)
Tomato blight is less likely in a greenhouse as it is encouraged by wet foliage.
Fruits can split if there is an imbalance in watering.

Question 20

List range of materials used for framework construction.
Describe and state benefits and limitations

Answer 20

Steel -
Rigid, strong and long-lasting (but must be galvanised)
Good for greenhouses/polytunnels
Can be welded for strong joints
Heavy - difficult to handle

Aluminium -
Used for greenhouses, frames & polytunnels
Sturdy yet light
Less expensive than wooden frame
Least bulky
Lightweight - easy to handle
Won’t corrode
Not attractive
More expensive than steel
Not easy to weld - have to use nuts and bolts to construct
Production is energy-intensive

Wood -
Traditional for greenhouses and frames
Can be softwood or hardwood
Hardwoods are more robust and won’t rot as quickly as softwoods,
But hardwoods are more heavy, bulky and expensive
Provides good insulation - retains heat
Bulkiness can cause more shade
Minor repairs are easily made
Wood rots, so sealer treatment every 1-2 years is necessary.

Plastics -
Plastic (UPVC) frames are good for conservatories
Durable and cheaper than wood
Not attractive and may not be in keeping with the garden style.
Plastic hoops can be used for low tunnels (clad in polythene or fleece)
Plastic is degraded by light over time, but can still last many years.

Brick -
Can form the base of a conservatory or the sides of a cold frame in a permanent situation.
Long lasting, strong and durable.
Expensive and skill needed to lay the bricks.

Question 21

Describe properties of different cladding materials - benefits and limitations!

Answer 21

Glass -
- Transmits highest levels of light
- Easily cleaned
- Won’t discolour
- Long-lasting
- Most expensive
- Easily broken - may crack or shatter
- Cannot be formed around corners, so not suitable for curved structures.

Polythene sheeting -
- flexible
- lightweight
- inexpensive
- only cladding material suitable for polytunnels
- allows a diffuse light which helps maintain light levels in structure
- can be degraded by sunlight
- becomes discoloured
- needs replacing after a couple of years
- more condensation, so good ventilation needed
- good for covering a broken glasshouse pane!

Polycarbonate -
- lightweight
- durable
- does not shatter
- good insulating properties, especially twin-walled
- can use in large sheets - does not bend
- easy to cut
- expensive
- can discolour over time
- scratches easily
- water condenses quicker on plastics
- needs replacement over time due to poor light transmission

Acrylic sheets -
lightweight
- durable
- does not shatter
- can be shaped during production (for curved structures)
- more brittle than polycarbonate but can be cut or drilled easily
- can discolour over time
- scratches easily
- water condenses quicker on plastics
- needs replacement over time due to poor light transmission

Shade netting -
- woven plastic netting
- used instead of polythene for shade tunnels (for e.g. ferns) to protect against scorching sunlight
- used inside greenhouses seasonally to provide shade
- fixed inside: shades plants from scorching sunlight
- fixed outside: helps reduce overall temperature inside greenhouse
- also used to construct windbreaks.

Horticultural fleece -
- soft, fibrous, spun plastic
- can be cut to size or sown into “jackets”
- insulator for a greenhouse
- insulator for soil and tender plants
- can be used over low frames instead of polythene.
- good flying insect barrier.

Question 22

Describe factors that affect LIGHT LEVELS in protected structures.

Answer 22

Shape of structure:
Venlo/ widespan/ Mansard/ curvilinear
Angle of incidence (light should ideally hit glass pane close to 90 degrees)
Aesthetics

Site factors:
Exposed/sheltered
Latitude

Orientation: E-W (for spring sun) or N-S (for summer sun)

Type and condition of cladding materials:
New?
Scratched?
Dirty?
Screened/painted with shading compound?

Question 23

Describe how TEMPERATURE can be maintained in structures

Answer 23

Heating using gas, electricity, paraffin, biomass (and relative costs)

Electricity: powers fans and convection heaters; efficient in smaller areas and controlled by thermostat; no harmful fumes; dry heat so will lower RH; costs more than gas heating; needs electricity supply to structure and waterproof sockets etc.

Gas: readily available and can be mains or bottle supplied; powers small heaters; powers boilers for large HW circulation systems; burning gas causes water vapour = increased RH; can emit fumes, so ventilation should be managed properly.

Paraffin: not commonly used now; emits fumes; cheaper than electric/gas heaters but not as efficient.

Biomass: a solid fuel that can be used to heat boilers.

Thermal screens and fleece can be used to keep greenhouse warmer in winter.

Cooling by forced or natural ventilation such as a fan one end and vents at the other end; louvre vents; top opening vents

Cooling by evaporation - damping off - spraying the floor surfaces with water to cool the structure

Shading - shade netting in the summer will keep the greenhouse cooler.

Question 24

Describe how to change the RH in a protected environment

Answer 24

RH can be raised by reducing ventilation and air movement, and by lowering the air temperature inside the structure.

RH can be raised by “damping down” - spray floor with water; as it evaporates it helps to raise the humidity levels and cool the space down; overhead irrigation methods and misting machines.

RH can be lowered by using electric heaters; increasing airflow and ventilation; increasing air temperature inside.

Temperature changes affect RH which in turn affect water and nutrient uptake.

Ventilation - hinged vents fitted in opposite walls and roofs to allow air in and out from either direction; louvre vents lower down in structure; open and close to control; also automated systems to open and close;

Forced ventilation = where vents on one side or end of the glasshouse draw in fresh air as the fan forces out hot and humid air at the end/side of the glasshouse.

[Polytunnels don’t have vents - achieve air flow by opening door or pulling back the sheeting.]

Question 25

Describe manual and automated methods of IRRIGATION - benefits and limitations

Answer 25

WATERING CAN -
Benefits - good for a small space; allows water to be tailored for each plant’s needs; easy and cheap.

Limitations - water is left sitting on leaves (can encourage disease)

HOSEPIPE -
- with spray head attachments

Benefit - good for larger areas; allows water to be tailored to each plant’s needs; easy and cheap.

Limitations - water is left sitting on leaves (can encourage disease)

CAPILLARY -
- potted plants placed on benches containing capillary matting. Mat can soak up and hold water. Compost (when dry) draws water up from the mat. Edge of mat sits in a water reservoir which can be topped up manually or on an automated system.

Benefit - can be fully automated (useful when going on holiday!); increases humidity; does not leave water sitting on leaves; low maintenance.

Limitation - increases humidity.

DRIP -
- network of small pipes fed by a larger pipe from mains; small pipes lead to individual pots.

Benefit - can work on an automated hosepipe timer; little water lost through evaporation; can water individual plants evenly (good for batches of same plants); does not leave water sitting on leaves; relatively cheap and easy to install.

Limitation - maintenance needed to avoid clogging of small nozzles.

Question 26

How can light levels be manipulated by use of supplementary lighting and shading?

Answer 26

Supplementary lighting is artificial lighting that is used to supplement daylight - extends the growing season; allows for crops and bedding plants to be grown earlier in the spring.
e.g. LEDs, high pressure sodium lamps, fluorescent tubes.

Shading -
Shading washes, blinds, netting and paints used to reduce effect of direct sunlight on greenhouse; often needed in spring and summer to prevent overheating.

Artificial light/dark period to prepare poinsettia crops -
- Getting poinsettias to flower again requires specific hours of darkness over a particular period of time to stimulate them to flower and even a small burst of light can interrupt this.
- Professional growers use special blackout blinds in their glasshouses to exclude all light from the plants to get them ready in time for sale.

Question 27

Describe importance of cultural and biological controls to limit damage caused by plant pests and diseases - + two examples of each!

Answer 27

CULTURAL control means good plant husbandry and making conditions less suitable for P&D. e.g. good hygiene, ventilation, air flow, physical controls like removing pests and using barriers.

e.g. - good ventilation can prevent fungal disesases such as Tomato Leaf Mould
e.g. - sticky traps to control Glasshouse Whitefly; misting plants can deter Red Spider Mite

BIOLOGICAL control means using beneficial organisms to control problem ones.

e.g. parasitoid wasp (Encarsia formosa) used to control Glasshouse Whitefly

e.g. ladybirds to control aphids.

Question 28

Advantages that cultural and biological control have over chemical control methods

Answer 28

Cultural controls benefit biodiversity and plant growth. They do not carry the associated risks of pesticides and pests do not build up resistance.

Biocontrols are very specific, only affecting the target problem organism. There is no waiting period for harvesting edible crops as with pesticides and they are often cheaper than chemicals.