Preparing for the Cold: How to Winterize a Greenhouse

Oct 29, 2020   

With the winter months fast approaching, every grower knows that now is the time to prepare their greenhouses for the onslaught of winter weather and cold temperatures. It is important for growers to winterize their greenhouse, so their grow can thrive even during the coldest winter months.

Winterization mainly consists of preventative measures to ensure a smooth transition into the colder months for an operation, so it is advised that growers begin this process in the fall. Starting winterization when temperatures have already gotten colder, or worse yet, not winterizing at all, can have detrimental effects on a grow.

Preparation is essential for a grow to flourish during the winter. Many steps can be taken to prepare a greenhouse for the winter, including cleaning the greenhouse from top to bottom, testing systems’ functionality and ensuring a greenhouse is properly heated and insulated. These are all vital aspects of an operation that need to be properly tested and prepared well before winter begins and temperatures start to drop. By doing this, growers will ensure their operation can combat the winter and keep their grow thriving.


Growers should carefully inspect every aspect of their greenhouse to make sure it is in perfect operating shape. Even the slightest damage or abnormality can cause huge problems for a grower and their crops. Broken equipment, systems or cladding can damage or even halt a grow. For example, a broken irrigation system could result in dehydrated plants and a broken heater could quickly cast crops into dangerously cold temperatures. This is why it is essential to inspect every aspect of the operation; anything that’s overlooked may be damaging to a grow.

Growers should also inspect their cladding for any rips, tears or holes. If there are any holes, they will allow cold air and pests to get into the greenhouse, and they will making heating a greenhouse nearly impossible. Heating with a poorly sealed greenhouse is inefficient and will quickly eat into winter profits.

It is also important to make sure the cladding is strong and can stand up to heavy snow and harsh winds, depending on the climate the operation is located in. Polyethylene film has a high tensile strength and comes in varying thicknesses, but may not stand up to strong winds or heavy snow. Double polyethylene film has added durability due to its two layers, and the middle can be inflated with air to provide superior insulation to the single layer film. Twin-wall polycarbonate is the most durable cladding option. It will stand up to inclement weather due to its rigidity and impact resistance. Twin-wall polycarbonate is even referred to as “bomb-proof,” so it can easily withstand just about anything thrown its way.

Next, growers should test all of their systems and ensure that they are functioning properly. Test heating, irrigation, fertigation and any other systems, and make any necessary repairs. It is important to make these repairs during the fall, so that the greenhouse is in perfect shape by the time winter rolls around and the weather gets colder. Failed systems can quickly become detrimental in the winter. While during the summer or fall a greenhouse could arguably last a couple days with a failed system, during the winter a grow could only last a couple hours – if not less – before succumbing to the elements.


It is crucial for growers to sanitize and clean every part of their greenhouse and its equipment to reduce the risk of pests and diseases. Growers should do this in the fall in order to have enough time to prepare for the winter season.

Start of by removing everything from the greenhouse and cleaning and disinfecting any benches or pots. This helps to keep pests away from crops. Then, clean and disinfect all of the greenhouse equipment. Bleach and hydrogen peroxide are both great options for cleaning and disinfecting, but always remember to dilute with water. A widely used cleaning solution for greenhouses is comprised of one-part bleach to nine parts water.

If a grower uses a hydroponics system, winterization provides the perfect opportunity to completely purge and clean the system. This ensures that the system is free of harmful pests, diseases and pathogens that can damage a grow, and gets rid of any build up from previous growing seasons.

Start by pulling all plants from the greenhouse. Then, clean and sanitize the entire system by cleaning out reservoirs, NFT channels and Dutch buckets, and then power washing and sanitizing the greenhouse from floor to ceiling. Lastly, repopulate the greenhouse and begin to grow. It may be helpful to start seedlings in a propagation room during the purging process, so they are ready to go once the system is properly cleaned.

Growers should also clean and disinfect their greenhouse cladding. Be sure to use a non-abrasive towel or sponge in order to avoid damage. After everything has been cleaned, growers can organize their greenhouse to optimize efficiency.

It is necessary to have a completely clean grow space at any time of the year, but preparing for the winter gives growers the perfect opportunity to deep clean and organize their greenhouse to start off the new season on a clean slate.

Heating and Insulation

The two most important things to a grower in the winter should be heating and insulation. Well before the start of winter, growers should test their heating system to make sure it is functioning properly. If growers wait until winter to do so, or don’t test it at all, they might find themselves in an emergency situation if their plants suddenly don’t have a heat source. It is also a good idea to have a backup heater for an operation in case of power outages or failure. A great option would be battery-powered heaters or gas heaters.

Growers should test their heating system and repair any part of it that is broken. It may also be a good idea to replace an old heating system with a high efficiency heater. One of the best high efficiency heaters on the market is the Modine Effinity 93 Condensing Unit Heater. This heater will provide a reliable source of heat while reducing energy costs. This heater is 93% efficient, so it is a cost-effective option monthly. It also protects against mold and maintains an even temperature with steady air circulation. While this heater may be an investment, it will pay for itself with energy savings.

It is also important to test thermostats and environmental controls to make sure they are functioning properly as well. An accurate thermostat is a must-have for any grow, so replace any inaccurate equipment immediately in favor of a newer, more precise option. Growers should also consider remote monitoring equipment if they haven’t already implemented it. Many of today’s greenhouse controllers allow growers to monitor their greenhouse from a separate location. This can provide peace of mind when growers can’t be on site.

A new high efficiency heater will get a grower nowhere if a greenhouse lacks insulation. Again, a common culprit for heat loss are holes in greenhouse cladding, as they let cold air in and allow warm air to escape, which is the opposite of what growers need during the winter. Completely sealing a structure is a simple and easy fix that improves insulation immensely.

Growers should keep the R-value of their cladding in mind when making decisions regarding winterization. For example, twin-wall polycarbonate cladding has an R-value of 1.72, which means it insulates well and prevents heat loss. This is due to the air pockets between the two walls providing superior insulation. Inflated double polyethylene film is a cost-effective option that also uses air pockets for better insulation, and doubly poly generally has an R-value of around 1.5. Single layer polyethylene film, on the other hand, has an R-value of .83. This is on the lower end, which will result in more heat loss and higher heating costs. Growers should make sure they have the proper cladding for their particular climate, and add extra insulation if they need more protection.


There are many steps growers can take to winterize their greenhouse, and each is important in a different way. It may be a bit time consuming and take a bit of effort, but being prepared for the winter and having a thriving greenhouse makes it worth the time. This is especially important for older greenhouses or greenhouses in colder climates, and these extra steps are sure to pay off with healthy, prosperous crops all winter long.


Janine Coppola