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4 Questions to Ask Yourself | Selecting
a Site for Your Greenhouse
Greenhouse Coverings | Greenhouse
Rule of Thumb
Thinking About Buying a Greenhouse
Eventually every gardener considers the purchase of a greenhouse. A greenhouse
offers the opportunity to enjoy gardening every month of the year. It also
represents a considerable commitment in money, time, and space. This guide
has been developed to help you select from the variety of available greenhouses.
You will want your greenhouse to meet both your gardening needs and your pocketbook. This
guide can help you decide what type of greenhouse best fits these requirements,
whether it is one from us or a different greenhouse.
1. What size greenhouse?
Greenhouse size is usually dictated by factors like available space and construction
costs versus need or desire. When choosing a size, consider if the greenhouse
will be used year-round, seasonally, or mainly as a sunspace. If you want a greenhouse
to house an extensive collection of houseplants, then it is best to plan on building
or purchasing a structure that is larger than your current space requirements.
Most hobby greenhouse owners find they need a larger greenhouse than they originally
thought. Upgrading later on may be more costly than ordering a larger unit
from the beginning. Another important size consideration often neglected
is height. You want to make sure your greenhouse has adequate head room. You need
to consider both peak and eave (sidewall) height. Taller houses are also easier
to heat and ventilate because the air has a greater buffer area.
2. What will the greenhouse be used for?
I want to get a head start in early spring and/or a few
extra growing weeks in late fall.
This is an easy task for a greenhouse. How much extra time the greenhouse will
provide will vary based on your local climate and if you choose to equip the greenhouse
with automatic ventilation and heating. Any of the greenhouses we offer can be
used for season extension since heating and cooling requirements are very low
for this purpose.
I am interested in overwintering plants that are not
hardy in my area.
Overwintering, maintaining the minimum temperature needed for plants to survive,
requires heating the greenhouse even if it is for a short period of time. Greenhouses
suitable for overwintering can also be used for season extending. Inexpensive
greenhouses like the FlowerHouse and Little Greenhouse are fine in milder climates
that you don't expect needing to heat the greenhouse more than about 30°
F above the outside temperature for any extended length of time.
If you are in a colder climate with temperatures that sometimes drop to 0°
F or below, a greenhouse with an insulated covering is recommended. These
greenhouses are not only retain heat better, but they also generally offer a tighter
seal than other greenhouses making them easier to heat. The Cross Country, Aspen,
and Sunshine models would be better suited for this purpose.
I want to grow plants in a greenhouse during the winter.
This is different from overwintering plants because plants generally need higher
temperatures to grow and thrive versus just staying alive. In this case, an insulated
greenhouse will be worth the extra investment because of the lower heating cost.
The Cross Country, Aspen, and Sunshine models are better greenhouses for growing
in the winter.
I want a greenhouse to grow plants year round.
A tightly sealed and insulated greenhouse with high light transmission is desirable
for year-round vegetables and flowers (especially in northern climates). Remember,
greenhouses are designed to store heat from the sun and create a warmer environment
inside of them, so use in the summer in most areas would be limited at best. A
greenhouse with a active ventilation system and evaporative cooling system will
be vital to keep temperatures at a minimum when it is hot outdoors.
A COMPARISON OF THE GREENHOUSES WE OFFER
3. How elaborate do you want the greenhouse to be?
If you are just starting seedlings or wintering over a few plants and are looking
for the least expensive option to do so, you should consider the FlowerHouse,
Little Greenhouse, and Portable greenhouses. All are great values. If you want
your greenhouse to be a focal point as well as functional, the Sunshine and Cross
Country greenhouses are among our most attractive structures. The Cape
Cod and Cottage series of the Cross Country are
available with a combination of glass and polycarbonate providing both beauty
4. Is a building permit required?
Check local ordinances for required setbacks from property lines, design requirements,
and other requirements. Call your local building department. Some hobby
greenhouses may not need a permit, but it is a good idea to check anyway.
a Site for Your Greenhouse
Choosing the right site for your greenhouse will not only determine how well it
works as a greenhouse, but how much you will enjoy it. There are several
factors to consider in choosing your site.
If the greenhouse is going to be used primarily for starting seeds and transplants
or plant propagation in the summer, place it in partial shade to minimize heat
buildup. You can use a shade cloth to control the amount of sunlight reaching
the interior if a partially shaded site is not available. If the greenhouse
will be used for growing in late fall and winter, or growing plants to maturity,
it will need maximum exposure to the sun. It should receive a minimum of
6 hours of direct sunlight everyday. It is best to position the greenhouse
with the ends facing east and west. This will provide more heat gain from the
sun during the winter and create less shadowing in the greenhouse. If the southern
exposure is restricted, but open to the east, southeast, southwest, or west, turn
the greenhouse to the winter sun. Remember the difference in sun angles from summer
to winter (the sun is much lower in the winter).
Sometimes a shade tree can be an advantage, providing some shade for the greenhouse
during the hot summer and letting the sun in after losing its leaves in the fall.
The problem with overhanging trees is one of falling branches that can damage
You want your greenhouse to be easily used. A good site should be sheltered from
high winds and easily accessible from your home and garden. Remember the need
to move soil, plants, fertilizer, and yourself to and from the greenhouse. Access
to utilities such as electricity and water are important requirements to remember
also when selecting your site.
Many regions have chronic weather problems such as heavy rain, snow, and/or strong
winds. Heavy rains may cause drainage problems in and around the greenhouse. To
avoid standing water, choose a spot on high well-drained ground or install a drainage
system before the greenhouse is erected. Snow is usually not a problem as long
as you provide adequate insulation and heating. Strong winds can be a real problem.
In cold weather, winds blowing over a greenhouse can drain it of its interior
heat escalating energy costs. Windbreaks are your most effective weapon. A windbreak
is an obstacle that "breaks" up the force of the wind. Trees, shrubs,
fences, and other structures can all be effective windbreaks. Remember that a
windbreak can also obstruct light. Try to locate one where it will block the least
amount of light.
4. Ease of construction and maintenance
A level, well drained site will obviously be easier to work with and maintain
than a low, swampy, or sloped area. It is also a good idea to locate your greenhouse
away from children's play areas.
What's the Best Material for Greenhouses?
There really is no best material for a greenhouse. It is hard to know what's best
when there are so many different materials used to make greenhouses. Aluminum,
galvanized steel, wood, PVC, glass, fiberglass, polycarbonate, polyethylene, etc. They
all have their place in greenhouse construction. Your needs and budget will determine
which is best for you.
Most important is the covering. It will determine the amount
and type of light reaching your plants, the overall appearance of your greenhouse,
its safety, ease of maintenance, and longevity.
- Glass -
Greenhouse Covering Insulation (R) Values
|4 mil polyethylene
||4 mm twinwall polycarbonate
|6 mil polyethylene
||6 mm twinwall polycarbonate
|6 mil poly double layer (inflated)
||8 mm twinwall polycarbonate
|11 mil woven polyethylene
||10mm twinwall polycarbonate
|3 mm glass (single layer)
||16 mm 5 wall polycarbonate
|Two layers of glass (insulated)
||Fiberglass or polycarbonate (single
R value is a commercial unit used to measure
the effectiveness of thermal insulation. A larger number represents a higher insulation
value and therefore greater heating and cooling efficiency.
Specific, brand-name, product R values may vary slightly from these figures.
The traditional greenhouse covering, preferred for its permanence and beauty.
Glass is one of the least efficient materials for retaining heat, because it transmits
heat and cold quickly and has very little insulating value (that's why it is used
in cooking utensils and thermometers). Greenhouse glass should be double or triple
strength to increase heating efficiency and decrease breakage which can be dangerous
when installing as well as a problem in the completed greenhouse.
Glass is much heavier than other coverings, requiring more substantial framing.
Other disadvantages include: it doesn't diffuse light, so there's a risk of burning
plants; glass breaks more easily than the plastic coverings (important if you
have hailstorms, trees nearby, kids that play baseball, etc.); and finally, slight
deviations from horizontal and vertical frame alignment or settling of the foundation
can crack it. Most glass greenhouses use either engineered aluminum, steel, or
laminated wood frames with full foundations. Never install glass on breezy
days. Because of the need for many smaller, overlapping, glass segments in these
greenhouses, site selection should take wind into consideration. Air (heat) leakage
is greater in glass greenhouses because of the many panes needed.
If you are unsure about your building talents, you might do well to avoid glass
as the frame must be absolutely square and rigid. If you must have glass, consider
hiring a contractor for your installation.
- Plastics -
These coverings include fiberglass, polycarbonate, acrylic sheets, and polyethylene
film. All plastics resist hailstone damage and are shatterproof, a distinct advantage
over glass. Rigid plastics are stiff, but not brittle. They can be flexed
to fit over a curved surface and are available in large sheets. This reduces the
number of potential air leaks by reducing the number of joints in the covering.
The first of the practical replacements for glass, fiberglass usually comes in
rolls or corrugated sheets and is translucent rather than transparent. You
can't see through it but light transmission is roughly equal to glass. Fiberglass
diffuses light that passes through it creating a virtually shadowless greenhouse. Fiberglass
retains heat more efficiently than glass (but not as well as insulated plastics
like multiwall polycarbonate or two layers of inflated polyethylene film) while
transmitting less heat into the greenhouse, a benefit in both winter and summer.
Its corrugated form allows overlapping sides to seal well but its undulating
ends can make for difficult joints. Aesthetically, the corrugations tend to detract
from the structure and grime can collect in valleys. Greenhouse fiberglass
is UV protected by a gel coat that will eventually be baked off by the sun lasting
only about 6 years before turning yellow. When this happens, dirt accumulates
among the glass fibers and becomes very unsightly.
One of the newest covering options, UV treated polycarbonate provides much of
the clarity of glass and is stronger and more resistant to impact than other coverings.
It is also more resistant to fire than other plastics. View
picture of polycarbonate
Polycarbonate is available in several different thicknesses and normally comes
in single, double, and triple walled sheets with many structural walls separating
its two flat sides. Single wall polycarbonate is the least expensive and is generally
used for its attractive appearance, but it lacks the strength, heat retention,
and light diffusing properties of double and triple wall polycarbonate. The multiwall
structure gives it greater strength and superior insulating values with the air
space built into the product. Multiwall polycarbonate also provides your
greenhouse with an even diffused light that minimizes shadow and is optimal for
growing plants. Another advantage of polycarbonate is its +15 year lifespan in
most areas. Triple wall is rather expensive compared to other covering options,
but it will pay for itself in reduced heating costs in cold climates that require
frequent heating. Double walled polycarbonate is used to cover the Aspen
and Sunshine greenhouses. Cross
Country greenhouses are available with double or 5 walled polycarbonate options.
A favorite of commercial growers (about 90 % of all greenhouse sq. footage in
the USA) because of its simplicity of maintenance. Use it for 3 to 5 years (life
depends on poly thickness and UV treatment used) then recover with new poly.
Used in single thickness, polyethylene film is good for simple cold frames and
greenhouses used for starting seeds and other seasonal needs. When two layers
are used, and the space between is inflated by a fan creating insulated air space,
the polyethylene film retains heat more efficiently than glass houses, saving
roughly 40% in heating costs.
Drawbacks to polyethylene film include a relatively short lifespan vs. other
coverings, possibilities of rips and tears, and a translucent appearance much
like fiberglass. Polyethylene's low cost, ease of replacement, high
light transmission, and good heat retention have made it a favorite of nurserymen
and commercial growers.
There are differences in polyethylene film. Cheap, thin films sold at many
hardware stores and home centers are unsuitable for greenhouse use. Those films
are designed as vapor barriers in home construction and other "interior" uses.
Greenhouse polyethylene films are specially coated for protection from UV (ultraviolet)
rays which shorten the lifespan of unprotected film. There's a minimal cost difference
and a considerable difference in performance on your greenhouse. The Little
Greenhouses use an advanced thermal film which cuts heating costs up to 15%
at night by reflecting thermal heat released from plants back into the greenhouse
and diffuses incoming light similar to more expensive polycarbonate coverings. The
FlowerHouse greenhouses use a new woven polyethylene
which is more durable.
Most greenhouse frames are made from wood, aluminum, galvanized steel, and PVC.
Which material is right for you depends a great deal upon where and how you will
be using your greenhouse.
Most commercial greenhouses have galvanized steel frames because they are long-lasting,
low cost, and require less framework (thus less shadowing) than any other framing
material thanks to steel's natural strength. Steel's greatest value in greenhouse
construction is its strength. You want as much light to enter your greenhouse
as possible and steel frames can be thinner than others, creating less shadow.
Its other big advantage is its low cost. Steel greenhouses are normally covered
with polyethylene film because most frames are not designed to accommodate rigid
panels without additional hardware. Be sure that any steel tube greenhouse you
purchase is made with heavy-duty galvanized or stainless tubing which is made
for outdoor construction purposes to protect it from a greenhouse's normal humid
and corrosive (fertilizer salts) atmosphere.
Galvanized metals will eventually wear off their protective finish and rust from
high humidity levels present in a greenhouse. Steel is much heavier than
aluminum and generally requires additional hardware to mount a rigid covering
Aluminum is used primarily in conjunction with glass or polycarbonate in architectural
sunspaces and hobby greenhouses. It can be anodized in a variety of colors and
has low maintenance requirements. Because of its higher initial cost, aluminum
is most often used with glass and rigid plastic coverings in structures like the
Aspen and Cross Country greenhouses.
Aluminum is the longest lasting of all of the framing materials mentioned because
it will never rust, rot, or break down from UV rays.
Aluminum does not have the strength of steel so frame members either must be
larger or more numerous. Look for engineered shapes in aluminum that are designed
to increase frame strength, because you want as little frame shadowing as possible
while not sacrificing the integrity of your greenhouse's frame.
Wood is most commonly used either for sunrooms or in homemade greenhouses.
They are popular because of their attractive look, the ease in which accessories
can be added to them, and the low amount of heat loss they produce compared to
similar size metal frames. Wood frame structures are most often covered with a
rigid plastic or glass. Though very attractive in sunspaces, wood has a limited
lifetime in a greenhouse's damp atmosphere before it starts to deteriorate. Redwood
(used in the Sunshine greenhouse frames) or cedar
is recommended because of their natural resistance to the elements and insects.
Applying a chemical sealant or stain to the wood periodically can also greatly
increase the life of the material.
Wood frames are generally larger and heavier than equivalent metal frames which
increases the amount of shadow in the greenhouse. Wood hobby houses are generally
small scale with a limited ability to expand once construction is complete.
Over the last 10 to 15 years plastic hobby greenhouses have become increasingly
popular. The main advantages of these greenhouses is their low cost, portability,
and ease of installation. Plastic is generally used to construct smaller structures
because it is not as rigid as metal or wood, but the introduction of options like
metal wire supports (included in Little Greenhouses)
compensates for what plastic lacks in strength. Plastic frames have become
increasingly popular because of the low amount of heat loss they produce compared
to similar size metal frames. This is because plastic is a poor heat conductor
The main drawback to a plastic frame is that ultraviolet rays from the sun will
eventually cause the plastic to deteriorate even if it is a UV protected material.
UV protected PVC materials generally have a 20 year or better life. Plastic frames
are also normally larger than equivalent metal frames which increases the amount
of shadow in the greenhouse.
Rule of Thumb
If you buy a greenhouse based solely on your current gardening
expectations, it will probably be too small within a year!
Greenhouse Supplies Guide >
Aspen | Cross
Country | FlowerHouse | Little
Greenhouse | Sunshine
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