Greenhouses 101: Styles and Materials
Frank Rauscher gives us the basics on greenhouse construction and the materials involved. He says the most important step in building your greenhouse is first figuring out what kind of plants it’s going to contain.
Greenhouses offer many benefits for professional growers and hobby gardeners alike and there are lots of different styles, materials and accessories out there to choose from. Many current greenhouse styles have a long history of use, but there are some innovations out there due to new technology—especially in the area of materials and accessories.
The amount of information available on this subject is almost overwhelming and I found that I could only cover a portion in an article of this size, so I would suggest that anyone thinking about purchasing or building a greenhouse might want to do a bit more research and just use this article as a starting point.
Planning a Greenhouse
The decision to build or purchase and assemble a greenhouse should come as the result of a careful plant review and a good understanding of the kind of protection the specific plant varieties you’re going to be growing will require. This assessment will be mostly based on your local climate and various plant characteristics, although protection from pests and even people can be important too.
If you are not sure what you’re going to grow yet, you won’t be able to determine what level of protection will be required. Don’t make a decision based on inadequate information—start your plan by knowing what you intend to grow, how much of it there will be and what features your greenhouse will need to include in order for you to be successful.
After you have decided which plants you want to grow and have done the research to know what kind of environment they’ll need in order to thrive, then you can choose what kind of greenhouse you’ll need. You won’t want to discover after your first growing season that you really needed a larger greenhouse, or one with different features, so plan well, build once and grow for many seasons—that’s my motto for greenhouse happiness.
Styles of Greenhouses
Tunnel and high tunnel designs have been around for quite a while and are one way of gaining greater control over the environment in an easy and cost-effective manner. Whether you’re growing vegetables, small fruit or flowers, these structures can do the job. The fact that the basic skeletal structure of a hoop house minimizes connectors makes this design both inexpensive and simple to set up.
Concerned about snow on the roof of your greenhouse? Snow weight can be an issue for standard hoop-tunnel style structures, but an option here might be gabled or gothic roofs—these have only a single added joining point, so construction will still be relatively simple. The angle of a gabled roof slope is steeper so it will prevent any buildup of snow that might damage or destroy the unit in cold climates.
Engineered greenhouses will naturally be more expensive in the design and construction phases, but can often provide cost or operational efficiencies down the road that make these up-front costs good investments.
When we talk about ‘engineering’ we’re generally referring to things like climate control or other special features required to grow certain types of plants, or operational conveniences—like roll-up and roll-down curtains or windbreaks or sliding, swinging or roll-up doors.
You’ll also find things like shade screens, circulation and exhaust fans, portable or rolling benches or even special flooring with radiant heating. Engineered greenhouses do not need to be large, but because the cost of design and construction are higher, their plans typically provide for a larger crop yield.
When the plan calls for a more basic greenhouse and the requirements are few, a kit can be just the thing. ‘Do it yourself’ is very popular today and a pre-designed kit can help take the complexity out of constructing your own greenhouse.
If this is going to be your first greenhouse and you intend to build it from scratch, you should realize that although this might be an exciting adventure it could also be just the recipe for unexpected and costly surprises—greenhouse kits can eliminate these risks and allow you to get set up and start growing in your new greenhouse with a minimum of difficulty.
There are of course many different kits on the market, so some research on your part will be required to make sure you get the right one. Just because it’s a kit doesn’t mean it has to be small—you’ll find a lot of options as far as size and design out there. A good first step will be to make sure you did your pre-planning effectively. Greenhouse kits can be the right decision for all kinds of applications—like community gardens, institutional gardening programs, commercial gardening businesses, plant nurseries, garden centers, market gardening operations, universities and schools, to name a few.
Hobby greenhouses are most often found in kit form and have design features that make the particular hobby in question (say, growing orchids) more convenient or likely to succeed. So if your need for a greenhouse is based on a particular plant or hobby, you might want to see if a design for that application already exists—this can save you a lot of time. Another style, the patio greenhouse, is typically smaller and designed to be conveniently located close to the house—convenience is the keyword here.
Traditional cold frame greenhouses are unheated, fairly small units with a transparent roof. Most often the roof is levered and can be opened. Generally these structures are built low to the ground in order to take advantage of natural ground warmth—their function is to provide temporary protection from cold temperatures and they are often used to start plants earlier in the season. Cold frames are most often stand-alone plant shelters, but are sometimes actually used inside of larger greenhouses that might not provide sufficient protection from cold temperatures.
Canopies and Tents
Perhaps the easiest greenhouse to assemble or build and the most affordable for its size, the canopy greenhouse is a good place to start for a lot of gardeners. These structures can be designed in several styles and will feature some kind of cloth-like material covering with an aluminum, polycarbonate or wood structure for support. Covering materials like Tyvek will add strength and durability to the greenhouse. Canopy greenhouses are generally easy to relocate and this portability can be very useful in the garden. Different designs can be employed for protection from cold or for shade protection in places where the summers are dry, hot and challenging for many plants.
There are several important issues to be considered when making your selection of greenhouse cover materials. The strength of your covering is going to be critical if strong winds or snow are likely to be encountered and the amount of light that will be able to penetrate the covering is obviously important in order to get the most out of your sunshine.
However, if the issues you are going to be facing are dry, hot conditions with excessive sunlight, the amount of light that you are able to shade becomes the most important consideration. You should also remember blue light encourages vegetative growth while most plants need red or orange shades in order to bloom.
Transparent and translucent plastic films are popular cover materials. The thickness of the film will determine its strength—a thickness of six millimeters is common, while a two millimeter cover is unlikely to withstand much mechanical stress or wind buffeting and is not recommended.
Often film coverings are manufactured with additives to prevent deterioration from ultraviolet radiation. These ‘UV inhibitors’ are not put into the material in order to block plant-required UV light, but to keep the material from degrading too quickly—very important! Some film materials are also mildew resistant.
Greenhouses are usually humid inside—although plants like this, it’s enough of a challenge to keep the mildew from damaging our plants without having it attack the very walls of our greenhouse.
Other covering features you can find are infrared retention (which retains desirable solar radiation), anti-condensation (which reduces precipitation from the covering) and tri-layer manufacturing processes (which improve cover strength). Recycled plastic baseboard and flooring is also available for your greenhouse, providing green benefits as well as superior greenhouse characteristics.
Polycarbonate panels are also available for use where wind and other stresses are substantial. Some of these rigid plastics are fully transparent—transparent corrugated plastic adds a significant level of strength and temperature protection and there is also clear bubble insulation that can be added for cold protection.
The permutations seem almost endless—sunblocker shade curtain, aluminet reflective shade screen and even liquid shade are all currently available options. They all seem pretty interesting—choosing the features and design for your new greenhouse can be kind of fun once you figure out what you’re looking for.