Written by H . Sierke (Gothic Arch Greenhouses INC. )

Best Greenhouse Options to Prepare for Winter: Top Tips for Cold-Weather Gardening

Winter gardening presents unique challenges, but with the proper preparation, your greenhouse can thrive during the colder months. Ensuring your greenhouse is equipped with the necessary tools and features is crucial to maintaining a steady environment for your plants. In this guide, we will walk through the best options for preparing your greenhouse for winter, covering insulation, heating, and cold-hardy plants.

Selecting the Best Greenhouse Insulation Materials

Insulation is key to maintaining a stable temperature in your greenhouse during winter. Several materials can provide effective insulation, ensuring that your plants are protected from the harsh cold:

Bubble Wrap

Bubble wrap is a cost-effective and easy-to-install insulation material. It traps air, which acts as a barrier against cold weather. For best results, use horticultural-grade bubble wrap, which is UV-resistant and designed for outdoor conditions. Simply apply the wrap to the inside of the greenhouse frame, securing it with clips or tape.

Polycarbonate Panels

Polycarbonate panels are a popular choice for greenhouse glazing due to their superior insulation compared to traditional glass. They are lightweight, durable, and provide better thermal regulation. The panels also diffuse light, helping to distribute sunlight more evenly inside the greenhouse during the shorter winter days.

Thermal Screens

Thermal screens ( e.g., Aluminum shade, Climate Shade, Solar Reflection Screens, etc.) can be automated to close at night, trapping heat inside the greenhouse. During the day, they retract to allow sunlight to enter. These screens offer a high-tech solution to maintaining a consistent temperature, reducing the need for manual adjustments.

Installing a Heating System

In colder climates, heating your greenhouse is often necessary to keep plants alive through the winter. There are several options depending on your greenhouse size and budget:

Electric Heaters

Electric heaters are user-friendly and ideal for small to medium-sized greenhouses. They can be thermostatically controlled to ensure the temperature stays within the desired range. While convenient, ensuring the greenhouse has a proper electrical setup to handle the heater's power requirements is essential.

Gas Heaters

Gas heaters are a more powerful option suited for larger greenhouses. Propane or natural gas can be used, but proper ventilation is critical to avoid gas buildup, which could harm plants and create a hazardous environment.

Solar-Powered Heating

Solar-powered heaters are a great eco-friendly solution. Though they require an initial investment in solar panels, they can reduce long-term energy costs. Solar systems work best in areas with ample sunlight, but supplementary heating may be needed during overcast days.

Maximizing Natural Light in Winter

With shorter daylight hours in winter, ensuring your plants receive adequate light is essential for healthy growth. Here’s how to optimize natural light in your greenhouse:

Supplemental Lighting

LED grow lights are excellent for providing extra light during winter months. They are energy-efficient, long-lasting, and emit the specific light wavelengths that plants need for photosynthesis. Position the lights above your plants and adjust the intensity based on the type of plants you’re growing.

Positioning Your Greenhouse

Maximize natural sunlight by ensuring your greenhouse is positioned to receive as much direct sunlight as possible. South-facing orientation is ideal in most regions. If your greenhouse is in a shaded area, consider trimming trees or other obstacles that block sunlight during the winter.

Reflective Surfaces

Reflective surfaces inside your greenhouse, such as walls painted white or using reflective foil, can help distribute sunlight more evenly. This ensures that plants in the corners or further from windows still benefit from available light.

Managing Humidity Levels

Maintaining the proper humidity levels in your greenhouse during winter is essential to prevent fungal diseases and ensure healthy plant growth. Cold air holds less moisture, so controlling humidity becomes a delicate balance.

Ventilation Systems

Good ventilation is critical to preventing mold and mildew in the winter. Opening vents for a short period during warmer parts of the day allows fresh air to circulate, helping to manage humidity without losing too much heat. Automated ventilation systems that open and close based on temperature and humidity levels can make this process easier.

Dehumidifiers

In highly humid conditions, a dehumidifier can be a helpful tool to reduce excess moisture. Modern dehumidifiers can be set to maintain a specific humidity level, ensuring your plants have the optimal environment without the risk of fungal growth.

Choosing Cold-Hardy Plants for Winter Growth

Not all plants can survive winter, but you can extend your growing season by selecting cold-hardy varieties. Here are some of the best plants to grow in a winter greenhouse:

Leafy Greens

Leafy vegetables like kale, spinach, and lettuce are excellent winter-growing choices. They thrive in cooler temperatures and can tolerate occasional frosts. These plants increase and can provide a steady supply of fresh greens throughout the colder months.

Root Vegetables

Crops such as carrots, beets, and radishes are also well-suited for winter growing. They need more soil insulation, but with proper preparation, these vegetables can be grown successfully in cold weather. Consider using raised beds or insulated containers to maintain soil warmth.

Herbs

Herbs like parsley, thyme, and chives are cold-tolerant and can flourish in winter conditions with minimal care. These herbs add variety to your winter garden and can be harvested fresh for cooking all season.

Efficient Watering Systems in Cold Weather

Watering your greenhouse during the winter requires careful management to avoid overwatering while ensuring that plants stay hydrated. Here's how to maintain an efficient watering system:

Drip Irrigation Systems

Drip irrigation systems provide a slow and steady water supply directly to your plants' roots. This method minimizes water waste and ensures plants get the moisture they need without oversaturating the soil. This can be a problem during the darker winter when evaporation rates are lower.

Self-Watering Systems

Self-watering containers are an excellent option for maintaining consistent moisture levels in small greenhouses. These systems store water in a reservoir beneath the soil, allowing plants to draw moisture as needed. This reduces the risk of over- or under-watering during the winter.

Water Temperature Considerations

In winter, it's important to avoid watering plants cold, as it can shock the roots. Use room temperature or slightly warmer water to keep your plants comfortable and avoid disrupting their growth. Additionally, water should be used early in the day so that any excess moisture can evaporate before nightfall, reducing the risk of freezing.

Implementing an Insulated Foundation

An often overlooked part of winter greenhouse preparation is the foundation. Insulating your greenhouse from the ground up helps retain warmth and provides a stable environment for plant roots.

Insulating Materials for Foundations

Use foam boards, insulated panels, or mulch to create a thermal barrier between the ground and the greenhouse floor. This prevents cold from seeping through the soil and helps maintain a more consistent temperature.

Raised Beds

Raised beds are a fantastic solution for insulating plant roots. The soil in raised beds warms up faster and retains heat better than the ground soil. Line the beds with insulation material or use straw and mulch to add another layer of protection against the cold.

Thermal Mats

For gardeners who want precise control over soil temperature, using thermal mats under planting trays or pots can provide warmth directly to the roots. This is particularly helpful for starting seeds or cold-sensitive plants that need extra protection in winter.

Utilizing Passive Heating Techniques

Passive heating methods harness natural energy sources to warm your greenhouse, reducing your reliance on artificial heating systems. These techniques are eco-friendly and cost-effective in the long run.

Composting

Composting generates heat as organic matter breaks down, making it an excellent passive heating method. Placing compost piles inside or next to your greenhouse can generate enough warmth to elevate the internal temperature by several degrees.

Thermal Mass

Thermal mass involves placing materials that absorb and store heat during the day and release it slowly at night. Water barrels, concrete, or large stones can be excellent thermal masses. Position them where they will receive the most sunlight, and they will radiate stored heat back into the greenhouse after the sun sets.

Cold Frames and Cloches

Adding cold frames or cloches inside your greenhouse creates a microclimate for susceptible plants. These structures trap additional warmth, providing extra protection against harsh winter conditions.

Ventilation and Air Circulation

Proper air circulation is critical in winter to avoid cold spots, condensation, and mold growth. Even though heat is essential, stagnant air can lead to plant disease.

Installing Ventilation Fans

Ventilation fans help keep air moving, preventing cold, damp air buildup in certain greenhouse parts. Automated systems regulating airflow based on temperature and humidity can ensure fresh air is introduced without losing too much heat.

Strategic Vent Placement

Vents placed at different heights help to balance air circulation. Install lower vents to allow cool air in and upper vents to release warm air that rises. This method ensures a steady airflow while maintaining internal warmth.

Using Circulation Fans

Circulation fans ensure that warm air from heaters or thermal masses reaches all corners of the greenhouse. Gently moving air around the space prevents cold pockets from forming and reduces condensation on plants and surfaces.

Greenhouse Monitoring Systems for Winter

Maintaining the right temperature, humidity, and lighting levels in your greenhouse during winter can be challenging, especially if you're not constantly monitoring it. Automated greenhouse monitoring systems can help keep conditions stable.

Automated Temperature Control

Automated temperature control systems can be programmed to maintain the perfect climate inside your greenhouse. These systems work by adjusting heating, ventilation, and cooling elements in response to temperature fluctuations, ensuring that your plants stay in an optimal environment day and night.

Remote Greenhouse Monitoring Apps

Modern monitoring systems often have apps allowing you to check on your greenhouse from anywhere. These apps can alert you to changes in temperature or humidity, and some even allow for remote control of heating and ventilation systems. This is particularly useful for managing the greenhouse during sudden cold spells or unexpected weather changes.

Humidity and Light Sensors

Advanced systems include temperature, humidity, and light sensors to give you a comprehensive view of your greenhouse conditions. These systems provide detailed insights, helping you make real-time adjustments to ensure your plants thrive throughout the winter months.

Solar Greenhouses: Harnessing Renewable Energy

Solar greenhouses are designed to maximize the use of natural sunlight for both heating and lighting, making them an energy-efficient option for winter gardening. With the proper setup, a solar greenhouse can remain warm and productive year-round, even in colder climates.

Overview of Solar Heating Systems

Solar heating systems capture sunlight during the day and store that energy to heat the greenhouse at night. This can be done with solar panels and thermal mass systems, such as water barrels or stones, that absorb and slowly release heat.

Passive Solar Greenhouses

Passive solar greenhouses are designed to maximize heat retention without relying on external energy sources. The structure uses angled glazing, insulated walls, and thermal mass to capture and store heat naturally. This type of greenhouse works best in areas with abundant sunlight and can significantly reduce heating costs in winter.

Energy-Efficient Design Features

Solar greenhouses often feature slanted roofs and insulated walls to optimize sunlight absorption and minimize heat loss. High-quality insulation and strategically placed thermal masses ensure the greenhouse retains heat even during the coldest months.

Preparing for Power Outages

Winter storms can sometimes cause power outages, which could affect your greenhouse’s heating, lighting, and ventilation systems. It’s essential to have backup plans to maintain a stable environment for your plants during these emergencies.

Backup Power Systems

Consider investing in a backup generator to keep your greenhouse operational during power outages. A generator ensures that your heaters and fans continue functioning, preventing temperature drops that could damage or kill your plants.

Non-Electric Heat Sources

In addition to a backup power supply, it’s wise to have non-electric heat sources like propane heaters or wood stoves on hand. These options can provide sufficient heat to keep your greenhouse warm during an extended power outage, though proper ventilation is crucial to prevent harmful gas buildup.

Insulating During an Outage

If power is lost, insulating your greenhouse as much as possible can help retain heat. Cover plants with frost blankets or row covers to provide extra warmth, and close vents to trap as much heat as possible until power is restored.

Maintaining Your Greenhouse Structure in Winter

Winter weather can be harsh on your greenhouse structure, especially in areas with heavy snow or strong winds. Proper maintenance and preparation can prevent damage and ensure your greenhouse remains intact throughout the season.

Snow Load Management

If your region experiences heavy snowfall, it's essential to clear snow off the roof of your greenhouse regularly. Snow can add significant weight to the structure, potentially causing damage or collapse. Installing a pitched roof can help snow slide off more efficiently, reducing the burden on your greenhouse.

Windbreaks

High winds can damage your greenhouse by causing structural strain or knocking it over. Installing windbreaks, such as fencing, trees, or hedges, can reduce the force of the wind hitting your greenhouse. This simple step helps prevent structural damage and reduce heat loss from wind chill.

Regular Inspections

Conduct regular greenhouse inspections throughout winter to check for any damage or wear, especially around seals, doors, and windows. Ensure that all bolts, panels, and joints are secure, and make repairs as necessary to keep your greenhouse weather-tight.

Insulating Greenhouse Doors and Windows

Greenhouse doors and windows are familiar sources of heat loss during the winter. Insulating these areas can significantly improve your greenhouse's ability to retain heat and maintain stable growing conditions.

Sealing Gaps

Check your greenhouse doors and windows for gaps where cold air can seep in. Use weatherstripping or caulk to seal these areas and prevent drafts. Adequately sealed doors and windows are vital to maintaining a consistent temperature inside your greenhouse.

Double-glazing 

If your greenhouse still has single-pane glass, consider upgrading to Double-glazing. 

Double-glazing provides much better insulation by trapping air between two glass panes, helping keep the interior warm during winter.

Insulated Curtains or Blinds

Adding insulated curtains or blinds to your greenhouse can provide additional protection against heat loss at night. These coverings can be closed in the evening to trap warmth inside and then opened during the day to allow sunlight to enter.

Effective Greenhouse Pest Management in Winter

Even during the colder months, pests can threaten your plants. Winter conditions may cause different types of pests to invade your greenhouse, so it’s important to stay vigilant and implement preventive measures.

Common Winter Pests

Some pests, like aphids, whiteflies, and spider mites, can thrive in a greenhouse's warm, humid conditions during winter. These pests can multiply quickly if not controlled, so regular inspections are essential.

Natural Pest Control Methods

Introduce beneficial insects like ladybugs or predatory mites to help keep pest populations under control. Insecticidal soaps or neem oil sprays can also effectively manage infestations without harming plants.

Maintaining Cleanliness

Good sanitation practices are critical for preventing pests in your greenhouse. Remove any plant debris, clean up soil spills, and regularly wash tools to reduce the chances of pests finding a foothold in your winter greenhouse.

Preparing your greenhouse for winter requires careful planning and the right combination of insulation, heating, and maintenance strategies. These steps allow you to create a stable environment that helps your plants to thrive, even in the coldest months. From selecting suitable materials to choosing cold-hardy plants, following these best practices will help ensure a successful winter growing season.

FAQs

1. What is the best material to insulate a greenhouse for winter?

Bubble wrap and polycarbonate panels are among the best materials for insulating a greenhouse, providing cost-effective solutions for retaining heat.

2. How do I heat my greenhouse in the winter without electricity?

You can use passive heating techniques like composting, thermal mass (such as water barrels), or non-electric heat sources like propane heaters or wood stoves.

3. Can I grow vegetables in a greenhouse during the winter?

In a winter greenhouse, you can grow cold-hardy vegetables such as spinach and kale and root crops like carrots.

4. How do I prevent mold in my greenhouse during the winter?

Proper ventilation is essential. During warmer parts of the day, use fans and open vents to circulate air and reduce humidity.

5. What are some tips for maintaining my greenhouse during heavy snow?

Clear snow from the roof regularly, install a pitched roof for better snow drainage and inspect the structure for any weak points or potential damage.