Not everything I use nor everything I do in a greenhouse will work for everyone. Each grow zone and even micro-environments within a grow zone can be different. We now live in an area that experiences high winds, so during our greenhouse research – high wind stability was a priority. Our old greenhouse would never have survived the first wind storm at our new home.
Variants such as wind, sun, location, county ordinances, slope of land, space, personal needs, etc. all play a part in determining the best type of greenhouse for you.
First recorded greenhouses
Around 40 AD, during the time of the Emperor Tiberius, Roman gardeners plant-ed some crops inside a barrel on wheels so that the plant could be easily transported into the sun during the day or inside to keep it warm at night. The barrels were stored under frames covered with oiled cloth or selenite.
Korea, in the 1400s, utilized a structure with an ondol – direct heat from wood smoke passing under a floor – and covered with oil hanji, which is traditional handmade paper from Korea. This allowed light penetration to grow Mandarin orange trees throughout the winter.
It is believed that in the 1800s, Charles Lucien Bonaparte, a French botanist, created the first practical working greenhouse. With the study of botany on the rise at that time, greenhouses start-ed popping up at universities all over – but they were far too expensive for the average citizen.
There are many different styles of greenhouses with a variety of roof and wall configurations.
Here is a list of the main types of coverings for extending the growing season.
Basic greenhouse types
Cold frames are unheated greenhouses. Small, cold frames are common in home gardens around the world; a simply built frame covered with plastic or glass to protect crops from frost. Cold frames are prevalent for commercial growers on a large scale, having standard widths up to 48 feet wide and as long as they need them. Another name for this type of cold frame is a high tunnel.
A hotbed is an individually heated small, cold frame. In a cold frame, the sun is the only source of heat whereas in a hotbed, sunlight is supplemental heat. There are many ways to heat a greenhouse. I plan to cover some in a future article.
A hothouse is a greenhouse generally maintained at a minimum of 55 degrees Fahrenheit.
An even-span is a self supported structure with equally sized rafters. The most common even-span structure is a traditional gable.
An uneven-span is the opposite. Uneven-span structures are not always self- supporting. They have rafters that are not equal in length and are usually found built on hillsides.
A lean-to is attached to another structure, such as a south-facing wall of a home or shed. It may look like half of a greenhouse that has been cut lengthwise. The ridge of the lean-to is attached to the building. This type is ideal for those with little space. A lean-to can utilize stability and radiant heat from the building to which it is attached.
An abutting greenhouse is similar to a lean-to. The difference is that the building the greenhouse is attached to forms the end of the greenhouse and not a side wall; the greenhouse is perpendicular to the building and the roof slopes to either side. An abutting installed in front of a home’s door makes a nice sunroom.
Conventional detached or stand alone greenhouses
These types of greenhouses are mainly defined by the style of the roofs. In colder climates, the north wall, and part of the roof on the north side, should be insulated to help retain heat.
A gable style has straight walls with a triangle sloping roof. This style roof allows plenty of room to move around inside, maximizes sunlight and, depending on its rise, helps prevent too much snow build up.
Flat arch roofs look like smushed hoops. This style roof is not ideal in areas that receive a lot of snowfall.
Tri-penta greenhouses were developed by the Phyto-Engineering Laboratory, USDA, in 1971. It has five sides of connecting triangles permitting maximum light and inside area with minimum framework. Fifteen equilateral triangular surfaces with 25 edges made of 10-foot long 2x4s are built by starting at the base and proceeding to the crown in five sections. These provide maximum inside area, but can be difficult to keep cool in the summer. Since the walls are all triangles, custom building support beams for adding fans, vents, etc. would be necessary. Another option for using this type in the summer would be to remove the plastic coving and install wire mesh, such as poultry wire, to the frame. Vertically grown plants such as beans and tomatoes could grow up the wire support. This creates shading for vegetables such as lettuce, which benefit from the cooler areas.
Ridge and furrow greenhouses are most commonly used by commercial growers. Multiple like sized even-span greenhouses are connected together along their lengths with the interior walls removed. This maximizes interior space on a commercial scale. These are also referred to as gutter-connected greenhouses.
Gothic is a hybrid between a gable and A-frame. The walls – like the curve of an egg – gently curve inward toward the top, forming a ridge point like a gable. This type easily sheds rain and snow.
An A-frame has long sloping sides that go all the way to the ground; forming a tall triangle. This style is easy to build with a minimal amount of supplies. It maximizes sunlight but can be difficult to work in since space is limited.
Quonset styles include hoophouses, igloos, domes and high tunnels. Simple Quonset style greenhouses and cold frames are easy to build with minimal supplies. Although the shape of these look like the wind would blow smoothly over the top, without properly anchoring them and using heavy duty materials, they can be prone to wind damage.
A sawtooth greenhouse has a split roof length-wise with one side higher than the other. Windows are usually installed here to help with extra ventilation and heat release. If this split runs East to West, reflective material can be placed along the back wall for added sunlight. Another option may be to store a thermal mass, such as water barrels, along the back wall where sunlight hits them, storing up heat for the night.
Skillion greenhouses have a flat angled roof. This type may be useful when the north wall is insulated, built into a hill, or made of some other solid construction.
A hybrid of a walipini, of my own design, is my next greenhouse build. Walipini greenhouses are dug into the ground, also called pit style. When built correctly, they are able to take advantage of the natural geothermal heat and large thermal mass of the surrounding earth and rock. Cooling in the summer can be just as important as warmth in the winter. Having this pit style greenhouse helps to regulate the inside temperature with milder fluctuations. Maintaining a moderate temperature fluctuation reduces stress on the plants.
Proper drainage and ventilation are more of a concern for pit style greenhouses. Not getting enough sunlight is another concern. Planning out all of the details before starting on a walipini is essential.
Do not believe all the hype about a walipini only costing $100 to build. While it may be true that a hole in the ground can be dug out and a covering placed over it for less than $100, a well planned out, functional walipini may cost considerably more. If this is your choice, completely research the pros and cons and plan out everything before starting on it, including how deep the frost line is in your area.
Shade houses are not greenhouses, but are generally used in warm to hot climates to protect light sensitive plants from sunburn or from drying out too quickly. Shade houses can have as many different shapes and styles as greenhouses, but they utilize a shade cloth to cover the supporting structure instead of glass or plastic. Air-flow is essential in a shade house. This type of structure is popular over outdoor hydroponic systems in warm climates.
Screen houses are covered with screen instead of glass or plastic. Mostly used in warm and hot grow zones, screen houses buffer the effects of severe storms as well as damage from insects and vermin.
One of the most common American greenhouses is an even-span freestanding traditional gable.
Grow zones range from 1 to 13, with the United States falling mainly among zones 2 to 10. This is a rough guide, which is based on an area’s long-term average annual extreme minimum temperatures.
I have had unheated, free standing, traditional gable, polycarbonate greenhouses. I have also built many small cold frames, both outside and inside the greenhouses.
I usually place some type of cold frame or hoop over my lettuce and other crops before the first freeze. Lettuces are cold hardy and can recover from some freezing but I still like to protect them.
TIP: When lettuces, and many other crops, get hit by a frost or freeze, go out to them with cold water before the sun hits them. Gently pour the cold water over the crop, completely drenching it, a water hose works well. The cold water melts the frozen cells. When the sun hits frozen leaves, the effects of the sun are intensified and can cause irreversible cell damage within the plant. If it is going to be a bright sunny day after thawing the crop, cover it with a very light weight cloth, such as gossamer or other frost cover, until after the sun has past its zenith. Each sequential freeze may weaken the plant. I have been using this trick since Granddaddy taught to me when I was a young child, and it has worked about 75% of the time.
My current 13×20 foot greenhouse, located in grow zone 5, is not heated, and is divided into four separate sections.
One section has a long bench for starting seeds and potting with room to store supplies under it.
Another area has a shelving rack with covered seed trays sitting on temperature controlled heating mats.
The third section is the center row. It consists of raised beds for cold hardy plants such as kale, cabbage, etc. This center row has a simple frame over it to support a single layer of plastic during the winter, when temperatures are near or below 0 degrees Fahrenheit.
The fourth area in my greenhouse has raised beds running the full length down one side. This area is for my warm climate plants. Although I live in zone 5, I have several zone 8 to 11 plants in this area. A few of these are: turmeric, galangal, avocado, lemongrass, etc. I also put tender herbs such as basil and a tomato or two in these beds over the winter. I will cover how to grow these heat loving plants in zone 5 in a future article.
Things to consider
• How much space do you have for a greenhouse?
• What is your budget?
• Are there any county or city ordinances that may limit what you can have?
• Do you have the skills and equipment to build one from scratch or do you need to purchase a kit?
• What zone do you live in? How hot does it get in the summer and cold in the winter?
• Will the primary use be for starting seeds, extending growing period a few weeks, growing plants year around, or as a sunroom?
• What type of plants will you grow in the greenhouse? If you want to grow trees inside then consider how tall and wide they will be at maturity.
• Will you need to heat it? If so, how far from the house will it be? What type of heat will you use? If using geothermal heating, plans need to be made before digging starts.
• Is your property mostly flat or does it have steep slopes?
• How much rain and snowfall do you get each year?
• How will you get water into the greenhouse – a water hose from house, is there a nearby creek that flows year round, gutter system to collect and store?
• Will you need drainage around the foundation? Look at where rain water puddles.
• What kind of foundation will you have? Dirt, concrete, gravel, masonry?
• If you plan to heat the greenhouse, the higher the roof, the higher the heating cost may be.
As you transverse through these general questions, do more questions come to mind? If so, write them down and consider them, as well.
In part 4, I will cover heating. Although it may seem like the foundation is the place to start, knowing how the greenhouse will be heated should come first.