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  3. Essential Guide to Greenhouse Ventilation and Heating

Essential Guide to Greenhouse Ventilation and Heating


Ventilation and heating are essential aspects of greenhouse management as it helps to regulate the temperature and humidity levels inside, which in turn promotes the healthy growth of plants. Greenhouses provide a controlled environment for plants to thrive, and proper ventilation and heating are crucial for their success. This article will explore the importance of greenhouse ventilation and heating and their impact on healthy plant growth.

Heater in a greenhouse, a concept of maintaining the required temperature in a greenhouse by means of additional heating with an electric oil heater

The Power of Temperature Control

When it comes to growing plants in greenhouses, temperature control holds the key to success. As a beginner gardener, grasping the impact of temperature is crucial for flourishing greenhouse cultivation. Let’s delve into the fascinating world of temperature control with these beginner-friendly insights:


Seeds have their own temperature preferences for germination. Each plant species requires a specific temperature range. Generally, warmer temperatures expedite germination, while cooler temperatures can delay or impede it.

Growth Rates:

Temperature directly influences the pace of plant growth. Warmer temperatures often result in faster growth, while cooler temperatures can slow things down. However, extreme temperatures—be it scorching or freezing—can harm plant development.


Temperature plays a pivotal role in photosynthesis, the process by which plants convert sunlight into energy. Within a certain range, increased temperatures enhance photosynthesis and boost plant productivity. Yet, excessive heat can hamper photosynthesis and disrupt the plant’s metabolic processes.

From Flower to Fruit:

Flowering and fruiting in plants hinge on specific temperature conditions. For instance, tomatoes and peppers thrive in warm temperatures, while lettuce and spinach prefer cooler surroundings. Mastering the optimal temperature requirements for flowering and fruiting is vital for a bountiful harvest.


Respiration is the process by which plants convert stored energy into a usable form. Higher temperatures escalate respiration rates, leading to increased energy consumption by plants. That’s why proper greenhouse ventilation is crucial to prevent overheating, which can stress the plants.

Guarding Against Pests and Diseases:

Temperature influences the occurrence and spread of plant diseases and pests. Some pests flourish in warmer temperatures, while others prefer cooler climes. By maintaining an appropriate temperature range, you can minimise the risk of pest infestations and diseases.

To unlock the full potential of your greenhouse, it’s crucial to monitor and control the temperature. Several methods can be employed, such as ventilation, shading, insulation, and heating or cooling systems. Additionally, selecting plant varieties that thrive in your greenhouse’s temperature conditions is paramount.

Remember, every plant has different temperature preferences. Therefore, it’s essential to research the specific requirements of the plants you are growing to provide them with an optimal environment. Regular observation, record-keeping, and adjusting the temperature accordingly will create favourable conditions for robust and productive plants in your greenhouse.

Greenhouse Temperature Guide: Plant-by-Plant Insights

Understanding the preferred temperature range for different plants is the first step toward creating an ideal greenhouse environment. Here’s a handy guide for some common greenhouse plants:


Tomatoes love warmth. The optimal temperature range for tomato seed germination is around 21-29°C. Once established, tomato plants thrive in daytime temperatures between 21-29°C and nighttime temperatures around 15-21°C. To encourage fruit setting, aim for daytime temperatures around 24-29°C and nighttime temperatures around 15-21°C.


Peppers also revel in warmth. The optimal temperature range for pepper seed germination is around 24-29°C. After germination, pepper plants flourish in daytime temperatures between 21-29°C and nighttime temperatures around 15-21°C. To ensure fruitful results, maintain daytime temperatures around 21-27°C and nighttime temperatures around 15-21°C.


Cucumbers are sun-worshippers. The optimal temperature range for cucumber seed germination is around 24-29°C. After germination, cucumber plants thrive in daytime temperatures between 21-27°C and nighttime temperatures around 15-21°C. Higher temperatures can promote rapid growth and fruit development, but be wary of excessive heat, which can stress the plants.


Lettuce is a cool-season crop. The optimal temperature range for lettuce seed germination is around 15-21°C. After germination, lettuce plants prefer daytime temperatures around 15-21°C and nighttime temperatures around 7-13°C. Higher temperatures can cause lettuce to bolt prematurely, impacting its quality.


Spinach also prefers cooler temperatures. The optimal temperature range for spinach seed germination is around 10-15°C. After germination, spinach plants thrive in daytime temperatures around 15-21°C and nighttime temperatures around 7-13°C. Warmer temperatures can induce spinach bolting.

Herbs (e.g., basil, parsley, cilantro):

Optimal temperature ranges for herbs can vary. Generally, herbs prefer temperatures around 15-21°C during the day and slightly cooler temperatures at night. Basil enjoys warmer conditions, while parsley and cilantro tolerate slightly cooler temperatures.

Remember, these temperature ranges serve as general guidelines, and variations can exist within each plant species. Furthermore, different cultivars within the same species might have slightly different temperature preferences. It’s always wise to consult seed packets, plant labels, or reliable gardening resources for precise temperature recommendations tailored to the plants in your greenhouse.

A Beginner’s Guide to Humidity Control

When it comes to greenhouse gardening, understanding the role of humidity is crucial for the well-being of your plants. Don’t worry if you’re new to this—let’s break it down in simple terms so you can create an optimal growing environment with ease.

Why Humidity Matters

Humidity is all about the moisture in the air, and it affects plants in several important ways. Let’s explore how it impacts your greenhouse garden:

  1. Transpiration: Just like us, plants need to cool off, and they do so by releasing moisture through tiny openings on their leaves called stomata. When the air is dry, plants transpire more to stay cool and obtain water from the soil. But in high humidity, the air is already filled with moisture, making it tough for plants to release excess water vapour. This can lead to reduced transpiration and even water stress for your plants.
  2. Disease Development: Humidity levels have a huge impact on the development and spread of plant diseases. Certain fungal and bacterial pathogens thrive in humid conditions. When combined with warm temperatures, high humidity becomes a perfect breeding ground for these troublemakers. Nasty fungal diseases like powdery mildew, downy mildew, and botrytis love the moisture and can wreak havoc on your plants.
  3. Foliage Health: Healthy foliage is the key to thriving plants. Low humidity can dry out leaf surfaces, causing wilting, yellowing, and leaf drop. On the other hand, excessive humidity creates a damp environment that invites fungi, moulds, and bacteria to take up residence on your precious leaves. This can lead to leaf diseases and reduced photosynthesis—something we definitely want to avoid.
  4. Pollination and Fruit Set: If you’re growing plants that rely on pollination, humidity is crucial for their success. High humidity can interfere with pollen movement, making it less likely for pollination to occur. This can result in poor fruit development and a disappointing yield. Sometimes, you may need to lend a helping hand by gently shaking your plants or even resorting to hand-pollination techniques in high-humidity conditions.

The Greenhouse Secret: Ventilation and Air Circulation

Now that we understand the impact of humidity, let’s talk about how to manage it effectively in your greenhouse. The secret lies in ventilation and air circulation—here’s what you need to know:

  1. Ventilation: Keep your greenhouse well-ventilated by opening vents, doors, or windows. This allows the exchange of air, helping to remove excess moisture and maintain airflow. Say goodbye to stale, humid air and welcome in fresh, invigorating breezes.
  2. Fans: Introduce fans to your greenhouse to boost air circulation. They’ll keep the air moving, preventing those dreaded stagnant pockets and encouraging healthy transpiration in your plants. The gentle breeze will make your greenhouse feel alive and vibrant.
  3. Watering Practices: Adjust your watering routine to match humidity levels. In high humidity conditions, be cautious about overwatering, as it can lead to waterlogged soil and excessive moisture around your plants. Finding the right balance is key.
  4. Monitoring: Stay on top of humidity levels by using a hygrometer or digital weather station. Regular monitoring allows you to identify periods of high or low humidity, empowering you to take appropriate actions promptly. Knowledge is power, after all.
  5. Dehumidifiers: If high humidity persists and becomes a recurring issue, consider using dehumidifiers. These handy devices will help you reduce moisture levels in the greenhouse, creating a healthier environment for your plants.

Create a Healthy Haven for Your Plants

By mastering humidity control in your greenhouse, you’re paving the way for a healthier growing environment, reducing disease risks, and supporting the overall well-being of your plants. Remember, it’s all about finding the right balance between moisture and fresh airflow. So, open those vents, introduce fans, and keep a close eye on humidity levels. Your plants will thank you with vibrant growth and bountiful harvests.

Improving Greenhouse Ventilation

When it comes to greenhouse gardening, one crucial aspect that every beginner gardener should pay attention to is ventilation. Picture this: it’s a warm, sunny day, and your greenhouse is basking in the glorious rays of the sun. While this may seem ideal, without proper ventilation, your greenhouse can quickly turn into a sauna, causing harm to your beloved plants. Fear not! With a few simple techniques, you can ensure that your greenhouse remains a comfortable and nurturing environment for your green friends.

Greenhouse in back garden with open windows for ventilation

Why is ventilation so important, you ask?

Well, during the period from spring to autumn, greenhouses are especially prone to overheating. Without sufficient air circulation and humidity control, the heat and dry atmosphere can wreak havoc on your plants. But don’t despair! By implementing proper ventilation techniques, you can recreate the tropical and subtropical conditions that many plants thrive in.

So, what’s the main goal of ventilation?

It’s simple: you want to prevent the temperature within the greenhouse from reaching levels that can harm your plants. As the temperatures rise, it’s crucial to gradually reduce and remove any shading. This allows ventilation to take the lead in controlling overheating. During cold winter nights, you can bring back the blinds and netting to limit heat loss.

Now, let’s talk about airflow.

There are three main areas in your greenhouse where air can enter and exit: the doors, the roof vents, and the side vents. Don’t underestimate the importance of these openings! Smaller greenhouses, especially those with a higher glass-to-floor area ratio, require a higher percentage of ridge ventilation. Sadly, this often gets overlooked, leaving amateur greenhouses vulnerable to overheating.

To ensure effective ventilation, keep an eye on the greenhouse temperature using a maximum-minimum thermometer. If the temperatures soar above 27°C, your plants may be in danger. Watch out for signs like leaf scorch and desiccation of tender young plants and shoots, as they indicate the need for shading and ventilation. On sunny days, throw open all doors and vents, and if the temperature remains high, leave them open at night too. In extreme heat waves, you might even need to remove some glass panes temporarily to help with ventilation.


While opening doors and vents is a good start, it might not be enough. That’s where shading comes into play. From mid-spring to early autumn, shading becomes essential to keep temperatures in check. However, remember that shading limits the amount of light your plants receive, and since plant growth depends on light, it’s crucial to use the minimum amount of shading necessary. For light-loving plants like tomatoes, provide as much light as possible. On the other hand, sun-loving plants like succulents may not need shading, but adding some can create a more pleasant environment inside the greenhouse.

External Blinds

When it comes to shading options, you’ve got a few to choose from. External blinds provide maximum cooling by blocking the sun’s rays from entering the greenhouse through the glass. While they can be a bit pricier and may interfere with vents, they are highly effective. If you prefer something easier to automate, internal blinds are a good choice. Though not as efficient at cooling, they offer shade when needed and come in various materials and shading degrees.

Shade Netting

Shade netting is a cost-effective option that you can place inside the greenhouse and secure with clips. While external fitting is preferable, internal placement can be more convenient. Keep in mind that the plastic netting may degrade over time, but it’s relatively inexpensive to replace.

Shade netting over garden greenhouse
Shade netting over garden greenhouse

Shade Paint

Last but not least, we have shading paints. These paints are diluted in water and applied to the outside of the glass in spring, with thicker applications added as the season progresses. In early autumn, the coating can be washed off. However, keep in mind that shading paints may not be suitable for unpainted timber structures or greenhouses glazed with acrylic or polycarbonate, as the paint can leave traces that are difficult to remove. Some shading paints are designed to become translucent when wetted, allowing more light to pass through.

By implementing proper ventilation techniques and utilizing shading methods, beginner gardeners can maintain a healthy and thriving greenhouse environment while minimizing the risks of overheating and heat-related plant damage. So, go ahead, equip yourself with these essential tools, and watch your greenhouse transform into a haven for flourishing plants!

Heating: Keeping Your Greenhouse Warm and Your Plants Thriving

As a beginner gardener, understanding how to heat your greenhouse is essential for creating the perfect conditions for your plants, especially during the colder months. Let’s dive into the world of greenhouse heating and explore why it’s so important.

Choosing the Right Heating Method

When it comes to heating options, electricity is often the top choice for beginner gardeners. While it may seem costly, electric heaters offer several advantages. They are easy to control, and most importantly, they don’t produce combustion byproducts like water, ethylene, and carbon monoxide, which can harm your precious plants. Gas or paraffin heaters are better suited for specific crops that require lower temperatures, but keep in mind that they may require more ventilation, which can reduce energy savings. While other sustainable heating sources like ground source heat pumps show promise, they are currently expensive and not ideal for small greenhouses.

Insulating Your Greenhouse

Proper insulation is key to minimizing heat loss and saving energy costs. Here are some simple tips to help you insulate your greenhouse effectively:

  1. Seal cracks, replace broken panes, and ensure that doors and vents fit tightly.
  2. Add a layer of bubble polythene to insulate your greenhouse. However, keep in mind that each layer of plastic reduces light transmission by about ten per cent, which can affect plant growth. Double-glazing also reduces light transmission.
  3. Use transparent mastic or flexible materials to seal any gaps, ensuring that your greenhouse remains intact even during windy conditions.
  4. Renew seals on doors and vents, and if needed, use plastic sheeting to cover any leaking areas while still allowing for proper ventilation.
  5. In larger greenhouses, you can use polythene and battens to create sections, reducing the area that needs to be heated.
  6. Provide additional frost protection by draping fleece over your plants during cold snaps. Alternatively, you can use roll-down blinds or thermal screens suspended above head height to cover the entire greenhouse at night.

Choosing the Right Temperature

Setting the appropriate temperature is crucial for saving fuel while ensuring your plants stay warm enough. While a minimum temperature of 3ºC (37ºF) can sustain many tender plants, there is a risk if the plants become damp. For greater peace of mind, it is recommended to maintain a minimum temperature of 7ºC (45ºF) or even 10ºC (50ºF). By using fleece and other protective measures, you can safeguard your plants at these fuel-saving temperatures.

Additional Insulation Methods

Here are some extra methods to enhance insulation in your greenhouse:

  1. Insulate the greenhouse with horticultural bubble wrap designed to withstand UV light. Opt for bubble wrap with larger bubbles for better insulation and light transmission. Secure it in place with pegs, staples, or tape, making sure your windows stay clean for maximum light intake. You can also use bubble insulation to wrap outdoor pots, protecting the rootballs and preventing cracking.
  2. On very cold nights, place frost-protection fleeces over your plants for added warmth without relying solely on heating. Remember to remove the fleece during the day to allow for proper light and ventilation. Another option is to use an extendable greenhouse cloche to protect border plants.
Frost protection fleece over plants in greenhouse
Frost protection fleece over plants in a greenhouse

The Importance of Heating Your Greenhouse

Heating your greenhouse holds several vital benefits:

  1. Temperature regulation: Many plants have specific temperature requirements for optimal growth. By providing heating, you can create a stable environment, extending the growing season and protecting your plants from freezing temperatures.
  2. Plant health and growth: Consistent warmth promotes healthy growth, reduces stress on plants, and helps prevent diseases caused by cold and damp conditions.
  3. Protection from frost: Heating prevents frost damage, which can be extremely harmful to plants, especially during the winter months.
  4. Maximising productivity: With a heated greenhouse, you can cultivate a wider range of plants throughout the year, allowing for continuous harvests and a more diverse garden.

Remember, maintaining appropriate humidity levels and proper ventilation are equally important to prevent excess moisture, mould, and rot. Regularly monitor and adjust these factors based on your specific plant requirements to ensure a thriving greenhouse environment.


In conclusion, proper greenhouse ventilation and heating are crucial for maintaining optimal temperature and humidity levels, ensuring healthy plant growth. By understanding the temperature preferences of different plants and implementing effective ventilation techniques, you can create a favourable environment for robust and productive plants. Additionally, managing humidity through ventilation and shading methods helps prevent disease and promotes foliage health. Finally, choosing the right heating method and insulating your greenhouse further contribute to maintaining a warm and nurturing space for your plants. With these essential practices in place, your greenhouse will flourish, providing you with vibrant growth and bountiful harvests.

For more articles on Greenhouse Gardening, click here.

Updated on April 10, 2024

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