Greenhouse Temperature Control

Achieving an optimal temperature in your greenhouse is one of the most important aspects of ensuring your plants grow as efficiently and healthily as possible. Whilst it’s important your greenhouse is warm enough to encourage plant growth, it’s essential that you don’t let the temperature get too high, as this can cause your plants to wilt and too much sunlight can scorch delicate foliage. 

In this section of our extensive greenhouse guide, we take you through all things ventilation, heating and cooling. 

What is the ideal temperature for a greenhouse?

The ideal temperature for your greenhouse is anywhere between 25-28 degrees Celsius, though it’s worth noting that with the fluctuating UK temperature, along with overnight temperature drops, you’re not going to be able to achieve these temperatures consistently throughout the year. 

We would recommend not letting your greenhouse exceed 29 degrees Celsius, as this will start to cause damage to your plants. It’s exceptionally important to keep a close eye on the temperature of your greenhouse, particularly on warm days and especially if you don’t have automatic vents or louvres installed. 

It’s equally important to keep an eye on your greenhouse when the temperature drops too, as frost can creep into your greenhouse during the winter months and wreak havoc on your crops. That’s where our great range of greenhouse heaters come in useful, keeping your plants at a comfortable temperature all year round. 

There are lots of gadgets and apps available to monitor the temperature of the greenhouse, but even popping a bog-standard thermometer on a ledge inside is going to be invaluable. Investing in something very simple will help to settle your anxiety when it comes to monitoring temperature.

How can I cool down my greenhouse?

If your greenhouse does exceed 29 degrees Celsius, you need to take steps to cool it down effectively. Opening the door is a good place to start, but you’ll also need to ensure that any vents or louvres are open too. This is where automatic vents and louvres come into their own, as they open and close to keep the greenhouse at an optimal temperature throughout the day, leaving you free to relax in the knowledge it is all happening automatically. Most automatic openers can be adjusted to open at different temperatures too, so you can decide what works for your plants.

You could also consider investing in greenhouse blinds, as they protect your greenhouse from direct sunlight on particularly warm days. Pairing blinds with adequate vents and louvres is a great way to cool your greenhouse down effectively throughout the summer with minimal effort.

If you are looking for a more cost effective way of cooling your greenhouse, many greenhouse owners will attach shading material internally, though this can be difficult to put up and take down on a daily basis. Other options include shading paint, which you can paint directly onto the greenhouse glass; some paints can be washed off, while others can be peeled off the glass. 

It is worth noting that external shading is scientifically proven to be more effective at reducing greenhouse temperatures than internal shading; it’s much better to stop the heat from entering the greenhouse in the first instance, rather than trying to fend off what has already penetrated the glazing.

One other very simple way to bring heat down is to wet the floor of the greenhouse. Get the hose or watering can, and give the ground a good soaking - this is an especially good idea if you have a paved or concrete base which absorbs more heat than soil. The act of evaporation will bring down the overall temperature.

If you really want to get clever with your cooling systems, you could look to implement complex misting and fanning systems with the aid of electrics, thermostatic controls and smart engineering. But this certainly won’t be an option for everybody.

How much ventilation does my greenhouse need?

This all depends on the location you live in and the plants you want to grow.

If you live in an area that gets especially warm in the summer months, then time and money will be well spent on enhancing the ventilation in your greenhouse. Although it is worth noting that no matter where you live, it is always beneficial to have more ventilation rather than less. Temperature control is key for greenhouse gardening, so giving yourself the ability to ventilate more (or less) is invaluable.

It will also depend on what kind of plants you want to grow, as different plants will favour more or less ventilation. Tropical plants, for example, will enjoy high humidity, while alpines enjoy a good stiff breeze.

Most makes of greenhouse come with one roof vent as standard or none at all, but unlike many, our Rhino greenhouses come with a minimum of 1 roof vent and 1 side louvre, with our Premium collection boasting the maximum amount of roof ventilation the structure can possibly handle.

If you’re unsure of how much ventilation you’ll need, feel free to contact our friendly team who will be more than happy to advise. 

How to stop greenhouse condensation

Stopping condensation is essential if you want to reap maximum growing benefits from your greenhouse. Condensation constantly building up in your greenhouse can cause several issues such as disease spreading among your plants and unsightly and unhygienic mildew build-up on the glazing which encourages pests and stops light coming in. 

Being able to control the overall humidity in your greenhouse is an essential part of the growing process; if the humidity is too high, it can interfere with plant transpiration, which inevitably slows down plant growth. On the other hand, if humidity is too low, it can accelerate transpiration to levels the roots can’t keep up with, leaving plants dry and wilted.

Whilst it can be frustrating when condensation forms in your greenhouse, you’ll be glad to know there are several steps you can take to remedy this. Here are some of our top tips for stopping greenhouse condensation:

Give your plants space

Ensuring your plants have enough space between them allows for proper air circulation. It’s crucial in your battle against condensation. Moisture can get trapped if plants are too close together, which increases the chances of condensation forming in your greenhouse. 

Don’t overwater your plants

Whilst it’s important to give your plants plenty of water, it’s also vital that you don’t overwater them. Overwatering will likely lead to pots sitting in stagnant water which is bad for the plants and the greenhouse environment. If you’re consistently overwatering your plants you’ll find that condensation is likely to form in your greenhouse, especially if you’re watering your plants late at night. 

Water early in the day

Following on from our previous tip, always try and water your greenhouse crops in the morning, as this vastly reduces the chances of condensation forming. If you water your plants early, there is enough time for any excess water in and around pots to evaporate whilst the sun is on your greenhouse during the day. Leaving your watering till late at night significantly increases the risk of condensation forming inside the greenhouse, as the outdoor temperatures fall. 

NB: When watering in the morning, try to do so before the sun is directly on the greenhouse, so your plants have time to take up water. Otherwise the water may evaporate faster than the plants can absorb it!

Make sure air circulation is adequate  

Whilst spacing plants appropriately will help air circulation, you’ll need more than just that to lower the condensation levels in your greenhouse. Maintaining greenhouse air flow with adequate ventilation is key for all greenhouses, so if you have a real issue with condensation, consider investing in additional vents or louvres to increase the overall air circulation. A combination of both these vents and louvres is ideal, as it creates circulation through convection from the bottom (louvres) up to the roof (vents). Within 30 minutes to an hour of opening vents in your greenhouse, you should see that all condensation has cleared. 

Shading options

In the height of summer, ventilating your greenhouse may not be enough to get the temperature down to a suitable level. This is where greenhouse blinds become extremely useful for Rhino Greenhouse owners, as they enable your greenhouse to cool down quickly and effectively by avoiding strong direct sunlight.

Greenhouse blinds are very useful if you’re growing tender plants or seedlings in your greenhouse, as some can be more susceptible to wilting under intense sunlight when compared to established plants. You’d be surprised how much damage can be done to your plants in a short time when it comes to overheating, so having ventilation and blinds on hand can help avoid any issues. 

Check out our selection of Rhino blinds today, you’ll find the following sizes on our website (please note these are designed to fit Rhino greenhouses only): 

• Rhino 2ft Wide Roof Blind (For 6ft, 7ft & 8ft Wide Rhinos)
• Rhino 2ft Wide Roof Blind (For 9ft, 10ft & 12ft Wide Rhinos)
• Rhino 4ft Side Blind
• Rhino 6ft Side Blind

Another important benefit of our patented Rhino blinds is that they have been designed to work with our autovents, so that ventilation is never obstructed while the blinds are in position. Louvres and roof vents will continue to open and close without issue when the blinds are pulled down. Allowing ventilation after pulling the blinds over your greenhouse is essential when temperatures rise. We place particular emphasis on ensuring our range of blinds allow you to ventilate, whilst also shading your plants. 

Image: Rhino greenhouse without blinds (left) showing autovent open; Rhino greenhouse with blinds (right) showing autovent open without obstruction from blinds.

It’s also worth noting that blinds can be deployed in the winter months to reduce heat loss from the greenhouse. This is especially important during colder winter nights when the temperature drops significantly.

Automatic Ventilation Options

As you can probably tell by now, having adequate ventilation for your greenhouse is important if you want your plants to grow at an optimal rate. Depending on the model of greenhouse you purchase from Rhino Greenhouses Direct, you will have one or more of the following ventilation styles installed as standard.

• Autovent Replacement Cylinder (suitable for Ventomax or Univent)
• Easy-Fit Automatic Louvre Opener
• Bayliss Automatic Roof Vent Opener

All our automatic ventilation accessories work are operated via a wax cylinder that expands in the heat of the sun, pushing the piston open and contracts as it cools, gently pulling the vent back into the closed position. These are simple and eco-friendly gadgets that last for years.

How to heat my greenhouse

During the colder months of the year, you may need to give your autumn and winter based plants a little extra heat. There are a few ways to heat a greenhouse

• Electric Greenhouse Heaters

The most common way of heating your greenhouse is with electric heaters. Allowing you to control the temperature of your greenhouse, electric heaters are a relatively cost-effective way to allow your plants to thrive all year round. 

We have a selection of greenhouse heaters on offer, check out our options below:

Bio Green Palma 2.0kw Electric Greenhouse Heater - Manual Thermostat - Coming armed with 2000W heating output and an air circulation of 163 m³/h, this heater will have your greenhouse back to a toasty temperature in no time. This product is more than capable of heating a 39 sq.ft. greenhouse and offers frost protection up to 100 sq. ft. If you are looking for a compact and cost-effective heating solution for your greenhouse, this is it.

Bio Green Palma 2.0kW Electric Greenhouse Heater - Digital Thermostat - Want a greenhouse heater that requires as little intervention as possible? Step forward the Bio green Palma, with a digital thermostat. With all the same heating capabilities as it’s manual counterpart, the digital version allows the user to easily select the desired temperature using the thermostat. This can be set to temperatures ranging from -50°C to + 99°C depending on just how cold (or warm) the temperature gets.

Bio Green Phoenix Stainless Steel 2.8kW Electric Greenhouse Heater - If you need to heat a larger greenhouse space, this model is the one for you. Capable of heating a greenhouse up to 100 sq. ft. and offering frost protection up to 180 sq. ft. this product is proven at keeping even the largest greenhouses warm in the coldest of winters. The Bio Green Phoenix comes with a frost detection function, circulates air at an impressive 450m3/hour and boasts one of the quietest running fans available on the market today. The thermostat allows you to monitor the temperature in your greenhouse and gives users access to temperatures between 0-26°C. 

• Bubble Wrap 

This may sound like a strange one, but stick with us. If you are looking for an inexpensive way to insulate your greenhouse, you could opt for bubble wrap as a more makeshift fix. Horticultural bubble wrap is commonly used to create an additional layer of insulation that helps to keep the heat in your greenhouse for longer.  If you want to find out more about bubble wrapping a greenhouse to keep your crops warm, take a look at our blog on the subject.

If you want to find out more about keeping your greenhouse warm in the winter months, be sure to check out our in-depth blog post that gives you plenty of eco-friendly and cost-effective ideas on how to effectively insulate your greenhouse and keep heat in.