(Placement of a Greenhouse)

By Michelle Moore 

Anthony J. D’Angleo in The College Blue Book said, “Wherever you go, no matter what the weather, always bring your own sunshine.”  While D’Angleo’s statement referenced one’s disposition, those of us with a greenhouse take his statement one step further - we make the sunshine!  In the Pacific Northwest, we have an average of 76.5 days without rain or overcast skies each year. Bringing sunshine into our days is a challenge we know something about.

Not many people will have the perfect place for a greenhouse. There are usually some trade-offs. Perhaps your greenhouse may not be as large as you would like, or it may not be an extension of your house. But that doesn’t mean you can’t have the greenhouse you’ve been dreaming of.  In some ways, having a greenhouse is like having a garage.  First, you will love having one! Once you get used to it, you won’t want to leave your plants or your cars outside again. Secondly, things in a greenhouse G-R-O-W! No matter how much room you start with just about any greenhouse eventually gets crowded. Like a garage; all the empty spaces mysteriously fill up.

If you are going to purchase or build a greenhouse, you’ll want it in the best place possible. The ideal location for a greenhouse has five attributes:

• enough space
• level and well drained
• maximum sun exposure
• easy access and proximity to your house
• protection from potential hazards such as falling tree branches.

If your location does not have all of the ideal attributes, chances are good that you can still reap the rewards of owning a greenhouse.  It’s better to have a greenhouse in a less than perfect site than not to have one at all. Let’s look at each of these attributes individually.

What is the best location? It depends upon how you will use your greenhouse and your constraints. Common wisdom is to purchase the largest greenhouse of the best quality your space and budget will allow. With that in mind, when purchasing a greenhouse you will identify your constraint: budget, or space, or both. The good news is that there are solutions for a small space and a small budget!  If budget is your primary limiting factor, you may want to purchase an expandable kit that you can add on to later when you are able.

Enough Space
If space is your constraint, then you may only have one possible greenhouse location.  In that case, the greenhouse you purchase will be based on size. Many greenhouse kits come in six and eight foot widths to fit in those small spaces. If you are watching your budget and have limited space, building your own frame may give you the best utilization of your site. There are a variety of coverings available in all price ranges.

To get started right away with limited funds, use a single layer of film plastic and upgrade to a better quality covering in a few seasons. The single layer covering will extend your growing season in the spring and fall by a few weeks. Adding an insulated covering later will add years of life to your structure and months of growing time to your season.  

Level and Well Drained
If you have several locations to choose from, identify the potential greenhouse sites.    The potential area must be fairly level and have good drainage.  If there is not a level space one may be created. However, don’t forget to factor in your time when estimating the project costs! Some greenhouses require a foundation and significant site preparation. Other greenhouses have either a supplemental or attached base and require little more than level ground. If the site is level and has good drainage, little preparation may be needed. Minimally, you will need a weed barrier. Ideally your flooring inside the greenhouse will provide additional drainage for excess water.  Many experts recommend using several inches of pea gravel over the weed barrier.  This type of flooring increases insulation, is easy to clean, and will not retain
excess moisture.

Maximum Sun Exposure
Sun exposure is the next most important consideration.  Plants need both light and heat in the winter, so maximizing winter sunlight will reduce heating and electric costs. Most experts recommend a minimum of six hours of light for optimum results.  Southern exposure is the best, with South East exposure second. If the proposed location does not have light all day, then morning light is preferable because it jump starts photosynthesis that continues through out the day. Ideally the greenhouse end walls will face East-West so the sun will run along the ridge of the greenhouse from sunrise to sunset.  This will distribute the most even light in the greenhouse. If the greenhouse covering diffuses the light, this placement is not as important.

Easy Access and Proximity to Your House
Selecting a location with easy access makes spending time in the greenhouse more convenient and enjoyable. After all, the most fun part of owning a greenhouse is using it!   A greenhouse placed close to the house will be used more than one that requires a long walk along a muddy path or a trudge through knee deep snow. Greenhouses near a house are easier to wire for electricity, plum with water and natural gas. Creative homeowners often find ways to capture heat from sources like dryer vents or adding covered buckets of hot water to the greenhouse on particularly cold nights.  

Protection from Potential Hazards
Shelter is a final consideration. Falling branches may cause significant damage, as can strong winds. Some greenhouses are designed to withstand harsh elements, but many are not. Internet forums are filled with stories of homeowners losing greenhouses to strong winds. Some greenhouses can withstand high winds if tied down, while others require some shelter from prevailing winds. If you live in a high wind area, make sure to ask how the greenhouse you are interested in will perform in wind, and how it will handle impact from projectile objects. It’s also a good idea to avoid bird’s nests if your greenhouse is made of polycarbonate. Bird droppings can visibly scar the coverings and may add further scratches when cleaned. If your greenhouse in a vulnerable location and the unfortunate does occur, you’ll be happy to know that some greenhouses are easy to repair.

Balancing the Five Factors
Now it’s time to choose the location based on a balance of the five factors.  If faced with the decision between a less than convenient Southern location and a Northern location with extremely easy access, think about how you will use the greenhouse.  Would you like to spend time in the greenhouse puttering?  Will you be able to monitor the environment frequently or do you prefer more automation?  The convenient location is important if you want to spend time in the greenhouse and do not plan to have automated heat, ventilation or water.  It’s less likely you’ll view your greenhouse as your oasis if you have to brave the elements to get there. The Northern location may not have the ideal sun. In that case you can add a grow light if your greenhouse has a place to hang a fixture, and the structure is strong enough to support the weight.  You may also need some additional heat if there is not enough solar collection during the day. (Also keep in mind that the winter sun is lower, so there may more shadows in the winter.) Supplemental heat is also effective if the greenhouse is covered with an insulated covering. The insulation will hold the added heat, although the higher operational costs are unavoidable without natural solar energy.

It may not be cost effective to operate a greenhouse all winter in a cold location that does not get full sun.  In this case, choosing the sunny location may be preferable.  If your site is not close to your home, your greenhouse operation will be much easier with some automation. Constant monitoring will increase your success. A mini weather station will monitor the temperate and humidity inside the greenhouse displaying the results in your home. Some models have a frost alarm that will alert you if your greenhouse temperature approaches freezing.

Thermostat controllers operate both heaters and automatic vents allowing you to set an exact greenhouse temperature. Additionally, programmable timers work well with grow lights and hydroponic units. Watering is also an issue, especially on warm spring days.  Aquamat self watering capillary mats or an Oasis watering system work well for intermittent watering.

You can mitigate the risks of an exposed location by carefully selecting the greenhouse you purchase.  Naturally, glass or a breakable material is more susceptible to damage from airborne objects. A strong frame is also important. Many greenhouses are made with panels that sit inside the frame. Any shifting of the frame may cause the panels to pop out of place under pressure. A tie-down or anchor system is a necessity for almost any location when the greenhouse is not attached to a foundation.   Selecting a greenhouse with a curved roof may also mitigate the risk of wind damage.  The curve of the greenhouse facing the prevailing wind will deflect the force.

As any greenhouse owner can tell you, greenhouse growing is addictive! There is nothing like harvesting ripe tomatoes in May or planting starts when it’s just warm enough to start seeds. No matter where you build your greenhouse, you will enjoy the benefits of growing your own food, starting flowers for your yard or just escaping the gray days.  In Oregon we often hear the phrase, “There’s no such thing as bad weather, just bad gear.”  This is true in our gardens as well. If we waited for perfect conditions to enjoy the outdoors, we would be waiting for 288.5 days a year! GG

Michelle Moore is the general manager for The Greenhouse Catalog. She is an Oregon State University Master Gardener and has nearly 20 years experience working with greenhouses. She lives in Oregon with her husband where they are gardening outside of a greenhouse for the first time. You can contact Michelle at This e-mail address is being protected from spam bots, you need JavaScript enabled to view it or your can visit their website at www.greenhousecatalog.com/garden .