Greenhouses and Ferns
History of Greenhouses
Greenhouses were used long before wealthy Europeans and Americans used them to grow oranges and pineapples
in glass structures called orangeries and pineries. In 30 A.D. Roman emperor Tiberius used "Specularium,"
a material painstakingly fabricated from tiny translucent sheets of mica to build structure designed to satisfy
Tiberius's cravings for cucumbers out of season.
In 1599 the first practical greenhouse was developed by Jules Charles, a French botanist. This was erected
in Leiden Holland and used primarily to grow medicinal tropical plants. One of the favorite plants of the
day was the Tamarind (an Indian date) whose fruit was made into a curative drink.
Greenhouses began spreading throughout Europe. The French, who had a love of a new fruit, the orange, began
building orangeries to protect the trees from frost. These structures were cumbersome. One structure built
by Soloman de Caus in 1619 in Heidelburg which held 340 orange trees. It had a removable roof that had to
be painstakingly put up and taken down during the frost season.
Experimenting with angled glass walls and heating flues to improve the efficiency of greenhouses went on
throughout the 17th century. New technologies and improved glass led to larger and more elaborate structures
that housed plants simply to please the eyes and palates of the European aristocracy.
The Palace of Versailles was an example of the elaborate efforts of the royalty to build bigger and more
spectacular orangeries. The Versailles orangery was more than 500 feet long, 42 feet wide, and 45 feet
high. It had a southern exposure for light and heat.
Despite the elaborateness of these structures, it was the Victorian age in England that ushered in the
golden era of the greenhouse. By the end of the mid nineteenth century glass was plentiful and the
prohibitive taxes were repealed. The wealthy began competing with each other to build the most elaborate
greenhouse, again primarily just to grow citrus fruits and rare flowers. Little thought was given to using
the greenhouse for a complete range of food production.
The soaring conservatory at Kew Gardens in England is a prime example of the Victorian greenhouse. There is
a replica in San Fransisco's Golden Gate Park called the Conservatory of Flowers.
In America, the first greenhouse on record was built around 1737 by Andrew Faneuil, a wealthy Boston merchant.
Like his European predecessors, Faneuil used it primarily to grow fruit. The concept spread slowly, since
almost all greenhouses were built for the wealthy. George Washington, perhaps the richest man in America,
craved pineapples and ordered a pinery built at Mt. Vernon so he could serve pineapples to his guests.
By 1825, greenhouses were becoming increasingly common. Many of the greenhouses were heated by
furnaced-warmed air; some were pit greenhouses built into the earth and heated largely by south facing
windows. This is a design that remains highly practical today.
Indeed, the modern concept of the greenhouse is simple and practical. No longer is it the private domain of
the monied class, but something anyone interested in gardening can have for relatively little cost. Today a
greenhouse can go virtually anywhere there is space; it can be attached to a house, placed in a backyard or
perched on a deck, roof or balcony. In addition, greenhouses are becoming more automated, reducing the time
and care owners much spend. With new materials available today such as aluminum, PVC piping, fiberglass,
acrylic, and polycarbonate panels as well as pressure treated wood, the consumer is assured that their
greenhouse will stand the test of time. Long gone are the days of shattered glass and overheated/under
heated greenhouses.
Who Needs a Greenhouse?
Anyone who wants to grow plants that will not grow in the local heat, cold, humidity, or dryness needs a
greenhouse. We take small steps with aquariums, fruit ripeners, candy jars, and plastic pretzel barrels.
We use these small containers to control humidity and place them where the temperature matches the plants'
needs. When we have too many plants or too large of plants, we need to consider a greenhouse.
Getting Started
The world of greenhouses is a magical one, a place where seasons and climates don't matter. In a greenhouse
exotic plants bloom, tropical fruits and fresh vegetables are ready to be picked even in cooler months or,
if your greenhouse is heated and insulated, in the dead of winter. The lure of a greenhouse is powerful.
When you walk inside, you cut yourself off from the world, you work in the soil and tend to your plants
oblivious to the weather outside. You can now grow species you've never grown before and try new gardening
techniques in a controlled environment.
In the past greenhouses were a luxury, today there are nearly 3 million hobby greenhouses in the U.S. and
the number is expected to grow...grow...grow. The Internet has some nice gardening web sites and greenhouse
builder's sites and there are scores of models from which to choose. You can research and build your own,
use step-by-step plans, buy a kit (you still have to put it together), or have a contractor build one for
you. Careful planning will ensure that your new greenhouse is suited to your needs. You must first select
an appropriate site where there is plenty of sunlight, then determine what type of greenhouse you want: the
size, style, and covering.
Planning Your Greenhouse
You must first assess your needs. How big a greenhouse do you need? Hobby greenhouse owners suggest making
it larger than you anticipate using, because once you start gardening you'll probably want to expand. In
many cases, the size of your property will dictate the size of the structure.
Rule of Thumb
If you buy a greenhouse based solely on your current gardening expectations, it will probably be too small
within a year!
Is the purpose of the greenhouse to grow foliage houseplants or to grow veggies and flowers?
A warm greenhouse that permits maximum light isn't necessary for foliage houseplants. If your like me and
use the greenhouse for both, take the sunny location and use shading (shade cloth or a large tree at mid-day
will do).
How elaborate a structure do you need?
If you simply want to start your garden early and are not worried about aesthetics, you can use the hoop and
plastic style. They are easy to assemble and portable, you can move the smaller structures to different
parts of the garden as the need arises. Most folks nowadays want something that will look good in their
backyards, perhaps complement their deck, gazebo or fence. These types of greenhouse would use a
polycarbonate or fiberglass covering and cedar or redwood for the framing and walls. More elaborate glass
enclosed structures that have cement foundations, heating and electrical systems are very expensive and not
a do-it-yourself project.
Is a building permit necessary? Are there local design ordinances? Must the structure be set back from the
property lines?
The basic rule of thumb some places is; if it's portable or you can take it apart you don't need a permit
(much like a fence or gazebo). If you start putting running water, heat, electricity and a cement
foundation, get a permit. Anyway, don't take my word for it. Ask your local building code people. As for
taxes, the same applies. If it's a permanent structure, it will be taxed (i.e., pools). In any case, it
is best to check with your local permit office.
The cost to maintain a greenhouse and supply it with heat, water, and electricity depends on energy costs
in your area and what type of greenhouse you build. In most parts of North America electricity is cheap but
it's cold in the winter. You must build an insulated greenhouse with an energy efficient covering such as
Lexan Thermoclear or (dual poly for hoop style) if you want to maintain your greenhouse in the winter. With
a small portable 1500-watt heater in a three-season greenhouse, one could start the season late in March
and continue to late October possibly without incurring the costs of increased taxes, permits, and a more
expensive structure. Of course, if you live in a warmer climate where it doesn't freeze, cooling would be a
concern in summer and you would use the greenhouse to protect your plants from rain and wind. In this case,
use whatever you can to shade the greenhouse from the midday sun.
Deciding where you're going to locate your greenhouse is crucial. Unless it's a portable model built from a
kit, it's there to stay unless you're willing to go to a lot of expense and effort to move it. The first
consideration is sunlight and it's important to locate the greenhouse where it will get at least 6 hours of
direct sun per day. The preferred exposure is southern, then southeastern, southwestern, eastern, and
western. A northern exposure is too shady for a greenhouse. An east-west facing greenhouse will get 25%
more light than a north-south as it presents more surface to the sun at a right angle. Take note of any
trees, fences or other obstacles that may shut off light for a major portion of daylight hours. Remember
that, after June 21st, the sun starts to get lower on the horizon, so that a tree that doesn't affect the
greenhouse in June and July may shade the greenhouse in May or September. Drainage is another key
consideration in selecting a site. Find a level spot. Do not locate it in a depression that will act as a
catch basin for rain and snow.
Also avoid a boggy area where the soil is always wet. Access to water and electricity is important. The
further away from the access point, the more laborious it is to run the utility lines. Consider too, the
difficulty in walking to your greenhouse in inclement weather.
Greenhouse Styles
The style of the greenhouse you select depends on such factors as how permanent you want the structure to
be, whether it will be free standing or attached to the house, your building skills, and the type of snow
loads in your area. The following are the major styles of greenhouses that can be built; the attached,
A-frame, Gothic arch and the span roof or gable.
Attached
Also called a lean-to, this type of greenhouse is an extension of the home. There is usually direct access
to the house, and water and electricity are easily extended to the structure. In northern climates, an
attached greenhouse should not be located under a sloping roof because of icicles and snow slides.
A-Frame
Simple to construct, the A-frame can be built in sections on the ground and then raised into place and
covered. Although the shape is ideal for heavy snow loads, it provides limited headroom and is difficult to
ventilate.
Gothic Arch
The gothic roofline is made from laminated strips over which a permanent covering is installed. Extremely
decorative, it is a challenging project, because of the layout and lamination of the arches takes time. This
style is a good choice for regions with lots of rain and snow; the curved sides keep precipitation from
collecting.
Span Roof
This freestanding style probably has the most typical and usable shape of any greenhouse. The interior
layout is extremely practical, and there is easy access for a loaded wheelbarrow through a door at either
end. A variation of the span roof design is the gambrel roof (barn-shaped) greenhouse, however it is more
difficult to build because of all the angles to cut.
Coverings
One of the most important decisions you must make is the choice of material to cover your greenhouse. You
will want a material that will let in the maximum amount of light while allowing the least amount of heat
to escape. As well it must be strong enough to withstand hail and heavy snow loads. Greenhouse glazing has
improved remarkably in recent years. In addition to glass, there is a wide range of plastic glazing in the
form of film sheeting and rigid panels. You may be confused by the many trade names for each type of
plastic. Discuss your options with a reputable greenhouse supplier or builder, and make sure the plastic is
for greenhouses.
Glass
The traditional covering for greenhouses, glass is the preferred material for permanence. It lasts
indefinitely although it does become brittle with age. Since glass is breakable, it is more difficult and
dangerous to install, and it also requires a much sturdier frame than plastic-covered greenhouses. Glass has
undergone many improvements in recent years. Among the most important is increased strength (double and
triple strength ratings) to resist breaking. Larger panes are also available and, because fewer structural
members are needed, more light can enter the greenhouse. Frosted and hammered panels can be used break up
the light rays for more even distribution. Other advances have cut down on heat loss. Double-walled
tempered glass reduces heat loss by about one-third. Low-emissivity, or low-e, coating, is another option;
it reduces heat loss without a corresponding loss of light. In addition to being energy efficient, low-e
glass reduces condensation, partially blocks ultraviolet rays, and makes the inside glass warmer to the
touch.
Film Plastic
A greenhouse covered with film plastic is one-sixth to one-tenth the cost per square foot of a
glass-covered structure. Although less permanent than glass, film plastic can be heated as efficiently as
glass. Previously, film plastic had a life span of about three months in summer and nine months in winter.
Newer, clear types that resist yellowing last three to five years and allow up to 89% light transmission.
Sold under many trade names, they are available in many thicknesses from 2 mil to 15 mil. The thicker the
film, the more expensive. Weather-resistant 4 mil thick polyethylene film plastic, is perhaps the least
expensive film plastic that makes a satisfactory covering for a hobby greenhouse. In choosing plastic film,
make sure you buy one that has UV protection. You can also buy a plastic film with an infrared inhibitor;
it cuts heat loss inside the greenhouse by up to 20% on a cloudless night.
Another way to reduce heat loss is to double-layer the plastic creating an air pocket for insulation. This
space can be 3/4 to 4 inches thick. Although there is some light transmission loss, heating costs are
reduced by one third. Another innovation in film covering is an anticondensate additive that allows
moisture buildup to run down the sides of the film instead of onto the plants. By removing the condensation
drops that block the sun's rays, this new type of film plastic allows more light into the greenhouse. In
addition, it helps stop disease infection by keeping contaminated moisture from dripping on the plants.
Rigid Plastics
These coverings, which include fiberglass, acrylic, and polycarbonate, come in corrugated and flat forms.
Shatterproof, they resist hailstone damage to varying degrees (polycarbonate being the strongest). Some
types of rigid plastics get dirty and do not quite let the same amount of light in as glass does. However, a
good wash with detergent and water will remove dirt or smudges. All rigid plastics retain heat well. For
example, fiberglass retains heat 4.4 times more efficiently than glass and 70.8 times more efficiently than
polyethylene film. Plastic panels have fewer lap joints through which heat can escape. Corrugation in some
types makes a very tight fit at lap joints, thus saving heat. The total amount of light transmitted through
fiberglass rigid panels is roughly equal to that transmitted through glass. Fiberglass actually has the
advantage over glass because it transmits less heat. During the summer a fiberglass-covered greenhouse
requires less cooling than a glass greenhouse of the same size. Fiberglass with PVC is a durable,
relatively lightweight material that resists damage from weather, ultraviolet radiation, and acid rain.
Recent improvements in plastics include the introduction of structured sheets. Available in both acrylic
and polycarbonate, these are double skinned (for insulation) or corrugated. Acrylic transmits light better
but polycarbonate is stronger and more resistant to impact and fire. Both materials can be used on curved
areas. When purchasing polycarbonate panels, make sure they are UV-coated to guard against premature
yellowing.
A local firm, San Diego Plastics, makes a variety of plastic coverings that can be used for greenhouses.
Greenhouse Frames
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.
Galvanized Steel
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 greenhouses are normally covered with polyethylene film. Be sure that any steel tube
greenhouse you purchase is made with tubing such as Allied Steel's Gatorshield. Allied Gatorshield is used
by virtually all manufacturer's of large commercial greenhouses. This tubing has extra thick galvanizing to
protect it from a greenhouse's normal humid and corrosive (fertilizer salts) atmosphere. Gatorshield is not
the same as galvanized water pipe. It is galvanized structural steel designed to support heavy weight.
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 price.
Aluminum
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 plastics for glazing in structures.
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
Wood is most commonly used either for sunrooms or in homemade greenhouses. Redwood or cedar sre normally
used because of their natural resistance to the elements and attractive look. Wood frames are generally
much larger and heavier than equivalent metal frames which greatly increases the amount of shadow in the
greenhouse. 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. Wood hobby houses are generally small scale with a limited ability to expand once construction
is complete.
PVC Pipe
Over the last 5 to 10 years PVC hobby greenhouses have become increasingly popular. The main advantages of
these greenhouses is their low cost, portability, and ease of installation. PVC is not as strong as metal
and wood greenhouse frames, but the introduction of options like metal wire supports help compensate for
what PVC lacks in strength. PVC hobby greenhouses are a good low cost solution for extending your growing
season, starting seeds, growing transplants, and wintering plants. If you are interested in growing year
round or live in an excessively cold (negative temperatures are common) or windy (80 + mph winds) area you
may want to consider investing in a galvanized steel or aluminum structure.
Operating Systems and Accessories
Ventilation
Ventilation is the single most important requirement for a greenhouse. Without good ventilation, a
greenhouse is nothing more than a solar furnace (you can use it very effectively during the summer for
drying fruit). Your ventilation system should be able to make a complete change of air every few minutes in
summer to keep temperatures in the greenhouse at a reasonable level. In hot climates shade cloth may be
necessary to hold temperatures in check. Winter ventilation needs are lower.
Heating
Heating is only necessary if you plan to use your greenhouse throughout the year. If you're using your
greenhouse to start seedlings and root cuttings in the spring, supplemental heating probably will not be
necessary. In mild climates, 12' x 12' and smaller model hobby greenhouses can be adequately heated with
electric heaters (make sure electric heaters are not exposed to water to avoid a dangerous shock). In cold
climates or with larger size greenhouses, you should use gas greenhouse heaters particularly where
temperatures regularly fall below zero. When heating with gas, it is best to use a vented heater, because
they vent harmful gases produced during combustion.
Shade Cloth
Shade cloth is the way professional growers keep their greenhouses cool during those long hot summers. It
is relatively inexpensive and is also good for providing shade for plants that don't grow well in the full
sun.
Flooring
The floor of your greenhouse should allow easy drainage of water. Gravel and brick or concrete stepping
stones laid over sand are probably your best choices for greenhouse floor covering. You will want to lay a
sheet of woven weed barrier under the floor covering to prevent weed growth. Weeds harbor many pests and
diseases. Wood slat floors are sometimes used, but they tend to get very slippery when wet.
Benches
You will want benches in your greenhouse. They make a world of difference in the ease of gardening, and they
also add a lot of extra working space to your greenhouse. Benches come in a variety of materials from wood
to steel to aluminum to plastic. Metal and plastic benches may last longer than wood, but wood tends to be
more decorative.
Build or buy a kit?
Once you know what kind of greenhouse you want, you must decide whether to build your own from a plan or
assemble a prefabricated model from a kit. Base your decision on such factors as your available time,
budget, and building skills. If you want to construct your own but are inexperienced, consider hiring a
carpenter to help you. If saving money is your goal, you may be able to do that by building your own,
especially if you are able to use scrap materials such as old windows and doors. Even if you buy new
materials, you can build a greenhouse for less money than prefab kits. On the other hand if money is not
an issue but your skills are then a kit is a logical choice. Kits provide everything you need, including
a lightweight foundation for some models. Before deciding on a kit, send away for catalogs and study them
carefully. A greenhouse company with an informative web-site can provide more information than a brochure
and you will always have a fresh copy on your computer. Make sure assembly instructions are included as
well as a list of any materials you may have to buy to outfit the greenhouse such as landscaping cloth,
gravel, patio blocks etc.
Choices, Choices, Choices
There are a huge number of choices in greenhouse size, styles, and materials. You should first research
your greenhouse to determine exactly what you want. If you have local gfreenhouse distributors, contact
them for information and advice. If you are like San Diegans, with no local greenhouse distributor, there
are a huge number of choices and loads of information in books at your library or on the Internet. There are
more than 20 distributors with web pages.