2. Learning objectives
1. Know a range of types of protected structure, and their
use in growing plants.
1.1 Describe a range of protected structures, to include
greenhouses, cold frames, polythene tunnels, cloches and
conservatories
1.2 Describe horticultural uses for each of the structures listed
in 1.1, including plant propagation, crop production, and
decorative display.
1.3 Identify the limiting factors of photosynthesis and respiration
2. Know the environment provided by a range of protected
structures.
2.1 Describe the environmental differences between the
protected environment and outdoors, including temperature;
humidity; light; concentration of atmospheric gases; air
movement; and irrigation requirements.
3. What is protected growing?
Using various man-made structures to
enclose and protect plants for some or all of
their life.
These structures can range from the
expensive and permanent such as
conservatories and greenhouses to the
cheap and temporary like cloches and
fleece tunnels.
All provide some control of the environment
in which the plants are growing.
4. Why use protected growing?
o To maintain a more stable temperature for
seedlings and tender plants
o To maintain humidity and thus reduce the rate
of transpiration
o To propagate plants by seed or cutting in a
controlled environment
o To grow plants that are not adapted to our
climate.
o To grow plants out of season for cropping or
decoration.
5. Photosynthesis
Carbon dioxide +water +light → glucose + oxygen
(when in the presence of chlorophyll)
o Takes place in the chloroplasts.
o Requires carbon dioxide, water, light, the right
range of temperatures and chlorophyll.
o These factors are called limiting factors
6. Respiration
Do not confuse with breathing in
animals!
The process by which plants release
stored energy from glucose produced
in photosynthesis.
Limiting factors – oxygen, water,
temperature and glucose.
7. Law of Limiting Factors
If a process is influenced by more than one factor,
the rate of the process will be limited by the factor
that is in lowest supply
Therefore if temperature is low (10°C) increasing
light intensity or carbon dioxide concentration will
not increase the rate of photosynthesis.
Why does this matter ? The slower the rate of
photosynthesis (or respiration) the slower the rate of
growth.
Manipulating these factors in protected
environments maximises growth.
8. Controlling the environment
Outdoors Protected
Temperature Widely variable Less variation – heating,
insulation
Humidity Wind and temp. affect More controllable – no
wind.
Light Natural variation Can be reduced by
cladding; can be
supplemented
Gas
concentration
Natural levels of oxygen
and CO2
CO2 can become limited
Air Circulation usually free Air movement reduced –
diseases, increased
humidity
Irrigation Water can be wasted,
rain is available
All irrigation must be
provided
9. Types of protected growing
structure
Vary according to cost, permanence,
size and degree of control they give of
the environment.
Uses vary too – propagation from
seed and cuttings, growing crops and
decorative display.
Greenhouses, poly-tunnels, cold
frames, cloches, conservatories,
fleece.
10. Uses of protected growing
structures
Wider range of plants possible (adding heating
increases this further).
Earlier crops – either by growing inside or starting
seeds inside.
Raising half hardy plants e.g. bedding.
Raising large numbers of plants from seed (no
‘field factor’) reducing waste.
Hardening off half hardy plants before planting out.
Raising cuttings and producing plants in bulk from
seed.
Later crops – protecting plants for harvest later in
the season.
Year round display
11. Greenhouses
The larger the greenhouse the more
even the temperature inside – small
spaces heat and cool quickly.
Different shapes available – glazed to
the floor or brick or wooden sides.
Site in an open position in a sheltered
site with good access and services
Orientation – north to south for even
light distribution (although east to west
is best for winter light)
12. Cold Frames
Sloping box with glazed or plastic lid
that can be opened on supports or
removed.
Used to harden off plants, root
hardwood cuttings, grow out of
season but cold hardy crops, over
winter hardy plants in pots and bring
on young plants.
Site south-east or south-west facing
not directly south.
13. Poly- tunnels
Usually used to grow crops – not
attractive.
Metal or plastic frames with UV
stabilised polyethylene covers.
Lighter and cheaper than
greenhouses – can be moved.
Diffuse light means plants do not
shade each other.
14. Cloches
Smaller, temporary covers used to
protect crops at the start and end of
the season.
Moved to protect the plant which is
growing in the open soil (no need to
move the plants)
Glass or plastic, can be tent or bell
shaped.
15. Conservatories
Used to provide a year round
ornamental display of tender and half
hardy plants as part of the home.
This dual use can lead to problems as
the air may be too dry and warm for
some plants to grow comfortably.
Not suitable for propagation or crop
growing.
16. Fleece
Woven polypropylene fluffy mesh
Retains heat well, allows rain to penetrate, light is
diffuse but reduced. Pushed up by growing plants.
Short lived and not easy to re-use (tears and
degrades quite quickly).
Provides some protection from cold for
overwintering crops and at the start of the season.
Can be used to protect from pests but fine mesh is
probably better due to heat build up in summer and
limited water penetration.
17. Learning outcomes
1. Know a range of types of protected structure, and their
use in growing plants.
1.1 Describe a range of protected structures, to include
greenhouses, cold frames, polythene tunnels, cloches and
conservatories
1.2 Describe horticultural uses for each of the structures listed in
1.1, including plant propagation, crop production, and
decorative display.
1.3 Identify the limiting factors of photosynthesis and respiration.
2. Know the environment provided by a range of protected
structures.
2.1 Describe the environmental differences between the
protected environment and outdoors, including temperature;
humidity; light; concentration of atmospheric gases; air
movement; and irrigation requirements.
