HOW TO SAFELY WINTERISE YOUR GREENHOUSE
Winterising your greenhouse is an essential process when it comes to ensuring that your plants survive the cold winter months. By keeping the space well-maintained, you can retain heat, protect plants from frost damage, and prevent costly repairs caused by issues such as frozen plumbing.
This guide by gardening expert Calum Maddock at HomeHow.co.uk will explore why it is important to winterise your greenhouse and when you should start the process, as well as taking you through everything you need to know to get the job done safely and effectively.
Why is it Important to Winterise Your Greenhouse?
Winterising your greenhouse is crucial when it comes to protecting your plants during the colder months. Many greenhouse plants are damaged or killed by frosty conditions, but taking the right steps will help you regulate temperatures and prevent injury from the cold. A winterised greenhouse will retain heat far better, so you can also reduce the amount of energy needed and save on heating costs.
Winter-proofing will fortify your greenhouse against weather conditions such as frost, wind, snow, and ice, which can cause damage to glazing, vents, doors, and the overall structure. In addition to this, by maintaining warmer conditions, you can extend your growing season and grow plants later into the autumn and earlier in the spring.
When Should You Winterise Your Greenhouse?
Timing is key when it comes to winterising your greenhouse. In general, you should plan to prepare the space for winter around 4 to 6 weeks before the first expected frost. Attempting to start the process later can risk exposing plants and structures to frost and cold before you have adequate protection.
Some key steps, such as removing tender plants, cleaning up debris, harvesting final crops, and checking structural integrity, can be started earlier, whereas insulation, heating preparations, sealing vents, and other cold protection steps should be done closer to when frost is expected.
In the next sections, we will explore the key steps you can take to prepare your greenhouse for the winter season.
Clear Out the Space
The first task is clearing out any dead plant material, debris and unnecessary items. This includes getting rid of any spent annual flowers or vegetables, as their dead foliage can become a breeding ground for pests and diseases. Relocate tender perennials that cannot withstand cold temperatures to an indoor space temporarily for overwintering care.
Eliminating clutter such as extra pots, trays, and tools will clear your workspace for winterising tasks, and all traces of soil, debris, and plant matter should be removed from benches, shelves, floors, and work areas. Harvest any remaining produce that you want to use over the winter, and compost healthy plant material that is no longer producing.
Deep Clean
Once your greenhouse is emptied, it is time to give it a deep clean. Sweep floors and benches to remove any dirt, debris, and leaves that have accumulated over the growing season before disinfecting the benches. Scrub down walls, glazing, doors, vents and framing using a mild greenhouse cleaner or bleach solution that should then be rinsed away, as well as an algaecide if needed for any algae or moss growth.
Make sure all floor drain grates are free of debris so that water can drain freely and pull any weeds growing in the footing around the perimeter. Finally, clean and sanitise any tools that will remain in the greenhouse over winter. Thorough sanitation eliminates the risk of pests and diseases surviving over the winter and helps to prevent infestations when plants return in spring.
Assess Structure
It is critical to examine your greenhouse structure closely and make sure that everything is in working order before the colder weather arrives. Inspect glazing to check for cracking, clouding, or other signs that the panels are degrading and replace any that are damaged. Also, look for any gaps, cracks, or rot in framing joints and re-caulk seals if needed.
Test the doors and vents to make sure that all openings are operating smoothly and tightly, adjusting or lubricating hardware as needed. Repair any sinking cracks or gaps in the foundation and assess the overall structure by checking for loose screws, corrosion, weathering, or any instability in the frame and supports.
Insulate Your Greenhouse
Adding proper insulation will help to regulate temperatures and retain warmth in your greenhouse. Bubble polythene draped over the interior framework is a great option for boosting thermal control while still allowing light transmission, and foam board or rigid thermal panels around the base will help to maintain warmer soil and root zone temperatures.
Insulate walls with sheeting whilst avoiding restricting airflow, and add breathable fabric row covers or thermal blankets to add flexible temperature regulation over plants and benches. It is a fantastic idea to mulch the floor with a deep layer of straw or leaves to prevent ground frost.
Protect Water Systems
Freezing temperatures can cause damage to plumbing and irrigation pipes, but thankfully, this is preventable. Start by turning off the main water supply and drain lines using drain valves and open taps to remove any remaining water. Wrap foam covers around exterior fixtures and pack insulation around the head of in-ground hydrants.
Disconnect any hoses and store them to prevent cracking from freezing temperatures, and drain and protect irrigation pipes, pumps, filters, and other components. Taking these steps will prevent costly repairs from burst pipes and other freeze damage.
Maintain Air Circulation
Stagnant air in your greenhouse can promote the growth of mould and mildew, amongst other problems, so maintaining good circulation is key. It is a good idea to run circulation fans designed for greenhouses at a low speed for gentle movement and keep some vents partially open, except during spells of extreme cold.
Avoid overcrowding plants on benches and allow adequate space for airflow around each plant. Constantly monitor for humidity and increase ventilation if condensation or high humidity becomes an issue. Proper airflow will help to reduce pests, regulate humidity, and provide your overwintering plants with fresh oxygen.
Prepare Heating Systems
Depending on the temperatures of the season and overwintering needs, supplemental heating may be required. Start by checking that your greenhouse unit heaters or other heating systems are in working order with no damage or defects, and for natural gas, propane, or other fuelled heaters, ensure that they are serviced and safe.
Prevent heated air loss by sealing any draught sources such as gaps, cracks, or vents near your heat source, but be sure to include sufficient venting to avoid the buildup of hazardous gases. Proper heating system preparation will provide reliable warmth and protect your plants from extreme cold temperatures.
Add Winter Crops and Plants
Once your greenhouse is fully prepared for winter, it is time to bring in your overwintering plants. Select hardy crops that are adapted to cooler weather, such as kale, carrots, lettuce, and parsley. Move frost-tender potted plants into the greenhouse and relocate vulnerable perennials inside, providing cold protection while allowing them to go dormant.
Monitor all crops and plants carefully for signs of cold, watering needs, frost damage, disease, or pest infestations. If needed, use heaters, thermal blankets, and warmth-retaining strategies to keep plants above their minimum temperatures. Selecting the right plants and maintaining ideal conditions will help them to thrive despite the challenges that winter poses.
Final Thoughts
Winterising your greenhouse is an important annual task that marks the end of one growing season and prepares you for the next. Taking the time to properly insulate, seal draughts, sanitise, maintain structures, regulate temperatures, and care for overwintering plants will reward you with vigorous growth and bountiful harvests when spring arrives.
MORE ABOUT THE AUTHOR… CALUM MADDOCK: Calum Maddock is a UK-based landscaper with over fifteen years of experience in the industry. As a gardening expert for HomeHow, Calum offers his expert advice to tradespeople and homeowners around the globe. He has also been featured as a gardening expert for a range of reputable publications.
