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Greenhouse 101: What you need to know to start your project

Updated: Jun 20, 2023

You don't jump headfirst into a greenhouse project the way you would jump down from a dive at the local pool on a hot summer day. There are several factors to consider before starting to build a greenhouse.

A greenhouse cannot be built until you have determined two things: what you want to grow and the feasibility of your business plan. The type of crop you want to grow will allow you to determine more adequately the greenhouse model, the budget allocated to it and the length of the production period. By studying the feasibility of your business plan, you will be able to evaluate impact factors such as the marketing strategy, your opportunities, the proximity of the market, the means of transportation that will be required, etc.

Once these 2 factors are determined, it will be time to tackle the greenhouse construction project. To do this, you will need to address the following 3 main points.

1. Greenhouse location

Whether you build your own greenhouse, assemble a kit or have one built by a manufacturer, it is essential to choose the optimal location to install it. To find your dream location, consider:

a) Orders, permits and covenants

Make sure there are no local ordinances, permits or restrictive covenants that could affect the construction of a greenhouse.

b) Soil type

In order to avoid rainy seasons or the risk of flooding, it is preferable to find a flat piece of land that will be safe from heavy runoff.

Also, since most vegetable production is done directly in the greenhouse soil, it is a good idea to have a soil test done to assess its fertility and nutrients. Stay tuned for unwanted contaminants in the soil that could end up in your food!

For more details on the soil testing process, click here.

c) Snow

In areas with particularly snowy winters, it should be anticipated that snow may accumulate on and around the greenhouse. In addition to potentially creating a cycle of melting and freezing that can damage a poor foundation, there is also a risk of heaviness with the accumulation of snow; if time is not taken to remove the excess or build a sufficiently strong building, then the risk of your greenhouse collapsing will just be a time bomb ready to explode.

d) The sun and the orientation of the greenhouse

Especially important in colder regions, your greenhouse should be located on a sunny site with the least amount of obstruction from trees. Remember that the angle of the sun varies at different times of the year: it will be higher in the sky in mid-summer and lower at other times of the year.

Sunlight and your geographic location can also influence the orientation of the greenhouse. Considering the colder climate of North America, the optimal orientation would be directly south or southeast to catch the morning light. In most cases, it is wise to avoid orienting the greenhouse towards the west, as the risk of overheating is greater.

However, in regions such as the northwest where the winter season is more cloudy, the orientation is less important. It should also be noted that at higher latitudes, during the summer season, the sun moves further north.

Of course, these recommendations are not absolute; take the time to examine your situation and make the right choice accordingly.

e) Water and electricity

Whether watering by hand, drip irrigation or a sprinkler system, it is necessary to have access to water nearby. If necessary, protect the greenhouse from freezing to avoid damage caused by the cold.

Electricity will be used for irrigation, light or heating. Plan your installations and connections accordingly.

f) Wind

If your area is prone to high winds, anchor and orient your greenhouse into the wind. Some ideas for protection from the wind would be to include a line of trees (without them blocking sunlight to the greenhouse) or an earthen berm.

Strong winds can damage your plants. One of the best options to avoid this would be to have a greenhouse roof with rolls up that will open and close automatically as they catch the wind.

g) Space available

You need to have enough space for your current and potential crop. There are many situations where growers need more space than they originally estimated.

Also, think in terms of production growth: allow for additional space if you expand or add a new crop.

2. Types of greenhouses and costs

Investing in a greenhouse depends above all on the use you wish to make of it. Your final purchase should suit your needs, your available space and also your budget. If you look at the price and size of the greenhouse, you can find a list in the Greenhouse Guide - What you need to know before building a greenhouse that presents some of the options available to you.

The 2 most common types of greenhouses are tunnel greenhouses and glass greenhouses. Although the latter has proven to be very versatile and suitable for overwintering, it is more common to see market gardeners working with tunnel greenhouse models.

This is the most interesting option for small producers who cannot afford to pay huge sums of money. Tunnels cover crops while keeping the soil warm, allowing production to start earlier in the year and doubling the usual annual yield. That's why we'll focus on this model today, but you can always read more about glass greenhouses if the idea sounds interesting.

Tunnel greenhouses are ideal for growing plants and vegetables for a good part of the year (or year-round, depending on the region and climate you are in). They are definitely the best choice for growers who are growing in the ground and want to increase their production yield. In addition to having a more attractive price than glass greenhouses, you can also find subsidies to finance the purchase and construction of your greenhouse. It is important to note, however, that these grants are not automatically awarded once the application(s) are submitted.

It is possible to build your own greenhouse from your own resources or even from a kit that can be purchased online. However, make sure you have quality, sturdy material that will stand the test of time and the vagaries of the weather. Otherwise, to make a wise choice adapted to your different selection criteria, you can always buy greenhouses from manufacturers.

Here is a short list of greenhouse manufacturers with various models:

3. Greenhouse equipment

It can be difficult to know where to start when taking on a large project like a greenhouse. Depending on your commitment and budget, you can add shelving, automatic vents, a misting system, a heating system, a fan, a tool rack and the list goes on. Think about what you really need, what you would like to have and what you have room for.

There are a number of essentials for building and using almost any greenhouse. The first thing to know is that any equipment with an ON-OFF switch can easily be automated, saving you time, energy and money on human (labour) and energy resources.

Typically, greenhouse equipment that can be automated includes:

a) Heating (boilers, unit heaters, hot water distribution)

Greenhouse heat sources include: hydronic (in-floor heating), geothermal, electric heaters, propane or natural gas heaters, biomass, furnace, etc.

The furnace is generally the most common choice and is very easy to automate. A universal model that we use as an example in our User's Guide is the Modine furnace.

b) Cooling and airflow (ventilation, pad and fans, A/C)

The purpose of a greenhouse is to capture heat, but it can get too hot in hot weather. You need ventilation or your plants will die. You can choose between natural or mechanical ventilation. Natural ventilation uses the outside wind and exchanges air through side and roof vents. It is possible to automate the opening and closing of the vents.

There are two types of mechanical ventilation: exhaust ventilation and positive pressure ventilation. Mechanical ventilation is essential for year-round production. It is also recommended for greenhouses be less exposed to the wind. It is also possible to automate this type of installation.

c) Humidity control (fog, ventilation)

Low air circulation, excessive humidity and high temperatures can also lead to mold, mildew and other plant diseases. It is possible to monitor the humidity in your greenhouse with a humidity meter or with an outdoor or indoor temperature and humidity sensor, both of which can be automated.

For more details on proper greenhouse humidity control, click here.

d) Irrigation (valves and sensors, misting, hydroponics)

Check the soil moisture regularly and water it if necessary to prevent your plants from drying out. However, be careful not to over-water so as not to drown your plants or unnecessarily increase the humidity level. It is possible to monitor the rate of water absorption in the soil and avoid overwatering with a tensiometer.

The 2 most common ways to irrigate are with valves or misters, both of which are easily automated.

To choose durable equipment adapted to your crops, here are some suggestions from greenhouse equipment manufacturers that can meet your needs.

Fight against parasites

Pests like sheltered conditions as much as your plants. The first step in preventing unwanted visitors to your greenhouse is to keep your greenhouse and gardening tools clean. Thoroughly inspect your plants for disease and pests before bringing them into the greenhouse.

Remove plants with insects or diseases immediately. Plant foliage can be sprayed with, for example, Safer® Insect Soap which will kill or deter many soft-bodied insect pests. Also, bring in the right insects to help control pests. You can also introduce pollinators for fruiting your plants and inoculate the soil with mycorrhizal fungi to help establish a healthy ecosystem.

Here is a list of the most common greenhouse pests:

- Aphids

- Fungus

- Midges

- Cutworms and other caterpillars

- Whiteflies

- Shore flies

- Slugs

- Bloodworms

Note that mice, shrews and snakes can move into your greenhouse and affect your production.


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