Glasshouses and Frames
Advantages and Disadvantages
Why have a glasshouse ?
• To allow some gardening to continue
irrespective of the weather conditions
• A wider range of crops can be grown
• Earlier fruit and vegetables can be obtained
• Half hardy plants can be raised from seed
• Large numbers of plants can be economically
grown from seed
Types of Glasshouses - Wood
Advantages
• Looks more at home in
the garden setting
• Better heat retention
• Less condensation
• Easier to put up hooks,
staging and shelving
Disadvantages.
• Expensive
• Requires treating with a
preservative every few
years
Types of Glasshouses - Aluminium
• Advantages.
• Maintenance free
• Light to handle when
erecting
• Thinner bars leading to
slightly better light
transmission
• Disadvantages
• Functional rather than
beautiful
Materials - Glass
• Advantages.
• Better light
transmission
• Better heat retention
• More permanent
• Disadvantages.
• Expensive
• Breakable
Materials - Polycarbonate
• Advantages.
• Cheap (in the short
term)
• Easy to handle
• Disadvantages.
• Limited life of cover 3 –
5 years
Shapes of Glasshouses
Traditional span:
• A good all-round glasshouse. The sides may
be of wood, brick or glazed to the ground.
The roof span gives a good headroom. Heat
retention is better if it is not glazed to the
ground.
Dutch light
• The sloping sides and glazing down to the
bottom gives maximum light transmission
and is good for crops grown at soil level like
tomatoes.
Lean-to
• This is made to fit against a wall. The warmth
and insulating properties of the wall will help
to raise the temperature.
Siting the glasshouse
• Open position: avoid positions where the glasshouse is
in the shade
• Shelter from the wind: wind may cause structural
damage as well as lowering the temperature within the
house.
• Access: access via a hard path is desirable
• Close to water and electricity: A water supply nearby
will be vital for growing crops. Electricity may be
needed for heat, light or running other equipment.
• Orientation: For the most even light distribution it is
best to have the house running from north to south.
Unheated
• Not frost free and cannot therefore be used for tender
plants. Extends the growing season with an early spring
and late autumn
• Allows half hardy plants to be raised from seed and
planted out when the danger of frost is past.
Unheated
• Protects from weather and
provides higher temperatures
in summer that will suit some
plants i.e. Tomatoes
• Hardy plants can be grown
over winter i.e. bulbs for early
spring flowering
• Suitable for alpines and other
plants that like to be protected
from rain and wind
Cool
• Day temperatures of 5 - 10˚C
and minimum night
temperature of 2˚C.
• Frost free allowing tender
plants to be over-wintered.
• Allows house plants and plants
for cut flower to be grown all
year round.
Temperate
• Day
temperatures of
10 - 13˚C and a
minimum night
temperature of
7˚C
• Allows some sub
tropical plants to
be grown i.e.
Orchids
Warm
• Day temperature of 13 18˚C and minimum night
temperature of 13˚C
• Allows sub tropical and
some tropical plants to be
grown.
• Propagation may be done
without additional heat
allowing for high volumes
• May require heating all
year round
Methods of Heating: Electricity
Advantages:
• most convenient
• Easy to automation with thermostats and timing switches
• Cheapest to run if thermostatically controlled
• Disadvantages:
• Requires an electricity supply
• Expensive to install if no supply nearby.
Methods of Heating: Paraffin
Advantages:
• Portable
• Cheap to install
• Gives off carbon Dioxide that may benefit plants
Disadvantages:
• Cannot be automated
• Low heat output
• Produces water vapour and condensation
• Some ventilation require giving some heat loss
Methods of Heating: Gas
• Similar advantages
and disadvantages to
paraffin although it is
possible to get
thermostatic controls.
Insulation:
• Insulation will raise the temperature in an
unheated glasshouse and reduce the cost of
heating in heated ones. Test have shown that up
to 40% of heating costs can be saved by lining the
inside of the glasshouse.
• The most appropriate insulation material is clear
or translucent polythene, bubble polythene is
particularly effective.
• Always bear in mind that any insulation material
will have the effect of reducing light at a time
when light levels are already low.
Ventilation:
• Ventilation is very important to
maintain an even temperature and
to replace stale air.
• A good guide is that the ventilation
area of the glasshouse should be
one sixth of the floor area, and
very small glasshouses would
benefit from even more.
• Very few commercially bought
houses meet this requirement.
Ventilation types
There are two basic types of ventilators found on glasshouses:• Hinged – one pane hinged at the edge
• Louvre – small, multiple panes that move in unison
The best arrangements for ventilators are:
• To alternate the ventilator on each side of the roof. The air would then
enter from one side, be diverted around the house and expelled from the
other side.
• As warm air rises, an even better arrangement is to have additional
ventilators at the floor level. The warm air in the house would escape
through the roof vents and fresh air would be drawn in from the floor.
• Automatic openers can be fitted to ventilators to allow the ventilators to
respond quickly to temperature changes.
• Extractor fans can also be used where higher level of ventilation are
required.
Shading
Shading can serve two purposes
• Help to lower temperatures
• Reduce the light intensity
Methods:
• Special shading paint can be applied to the
outside of the glasshouse. At the end of the
season this can be easily washed off.
• External and internal blinds, these can be made
of a variety of material.
Watering Systems
• Because of the higher temperatures more water will be
required than in the open garden.
• Watering Can: – very useful for small seedling and
small numbers of pot plants
• Automatic systems: useful where a large number of
plants need to be watered.
• Basically there are FOUR methods of automatic
watering systems available.
•
•
•
•
Capillary systems
Spray systems
Drip feed systems
Seep hoses
Watering Systems
• Capillary systems- in the past fine sand was used
but this is very heavy when wet, today special
capillary mats are available made from woven
polyester. The mats can be wet by various
automatic methods
• Spray systems – Commonly used in commercial
glasshouse, where large areas can be watered at
regular intervals. They are limited in most small
glasshouses as the spread is wider than most
houses and can lead to water wastage.
Watering Systems
• Drip feed systems – most commonly used
system. Small bore pipes deliver water to
small drip feed nozzles. These nozzles can be
adjusted to regulate the amount of water
supplied.
• Seep hoses – can be used where crops are
grown on the soil. Water seeps out of very
small holes in the material.
Watering Systems
• Automatic systems - two main types available
• Timers that will turn the water supply on or
off for a period of time each day
• Sensors that will turn the water supply on or
off depending on the compost moisture or the
humidity levels.