The ideal temperature to grow tomatoes in a polytunnel is between 70°F and 80°F during the daytime. But what temperature should a polytunnel be at night? Throughout the night, it’s well-advised to maintain the polytunnel temperature in the United Kingdom between 60°F to 65°F.
Keeping these temperatures ranges from daytime to nighttime will help you grow tomatoes with a high yield. However, keep in mind that both excessively high and low temperatures can also cause problems. Very high temperatures can yield unmarketable tomatoes, while very low temperatures can affect your plants’ health.
Daytime temperatures
Tomatoes will grow effectively at a daytime temperature between 70°F to 80°F. This range is because the light conditions outside will determine which end you should use in the greenhouse. Simply put, you should go as low as 70°F on a cloudy day and then go up as 80°F on a clear day.
Depending on your region, you get the idea of how to determine which end of the range is appropriate for the day. To expand on it, the low range is best on a cloudy day because of the low light intensity and high temperature in that condition. Therefore, the tomatoes will also have a lower rate of photosynthesis.
On the contrary, bright days require you to put the polytunnel temperature at the high end of the range because of the high light intensity. In some regions, you can even go as high as 85°F. The bottom line is to use the light conditions as your deciding factor for the daytime temperature adjustment in the greenhouse.
Nighttime temperatures
During the nighttime, the greenhouse’s ideal temperature range should be between 60°F to 65°F. Remember that tomatoes, in particular, are more sensitive to cool temperatures compared to other crops. So at night, you mustn’t go lower than 60°F if you want to avoid pollination and fruit development problems.
What happens when the temperature is too high in the greenhouse
When your polytunnel temperature gets too high, it can affect the development of your tomato fruits. This is especially critical when it’s hot outside, and your polytunnel exceeds 95°F. You’ll risk abnormal colour development on your fruits, and you’ll delay the plant’s root growth.
What happens when the temperature is too low in the greenhouse
Having a very low temperature in the polytunnel is also as influential for growing tomatoes. If the polytunnel reaches a temperature below 60°F, you risk nutrient deficiencies in your plants. As a result, they become more susceptible to growth abnormalities and fungal infections.
How To Maintain The Ideal Temperatures For Growing Polytunnel Tomatoes
It’s crucial to maintain the ideal temperatures from daytime to nighttime in your greenhouse. You can achieve this by using a thermostat, effective ventilation system, alternate heating system, evaporative cooling system, and modifying the polytunnel roof.
Using a thermostat
Having a thermostat will give you an idea if your polytunnel maintains the ideal temperature for the tomatoes. It would help if you placed it at the plants’ blossom height or near the centre of the polytunnel for efficient control over the temperature. Check the thermostat several times throughout the day, especially when the temperature outside gets very high.
To make sure you’re getting an accurate reading, examine the placement of the thermostat as well. The sun should not be hitting it directly, or otherwise, it will read a higher temperature. Please put it in a shaded area or inside an aspirated box for an accurate reading.
Effective ventilation system
In addition to using a thermostat, the polytunnel should also have an effective ventilation system to keep the temperatures under control. You have the option to use side vents or automated roof systems to maintain the proper air circulation in the greenhouse. The decision lies in whether you want to open the vents when needed manually or if an automated system is more convenient for you.
Overall, you want an effective ventilation system for air exchange and air circulation to prevent condensation and fungal growth. At the same time, ventilation affects the humidity of the greenhouse. Make sure you’re consulting a professional when it comes to the installation of your ventilation system.
Alternate heating system
A standard alternate heating system for greenhouses that grow tomatoes is the use of heating pipes. This system is handy if you want to heat your polytunnel from the base. The pipes warm the air at ground level, forcing cool air at the top of the polytunnel to downward.
Evaporative cooling system
If you need to cool the greenhouse, an evaporative cooling system is your best solution. This is because it uses water for cooling the air, which also makes a moist and humid environment. If you live in a UK area where it gets scorched, an evaporative cooling system will help keep your plants healthy.
Modifying the polytunnel roof
You can increase the greenhouse’s roof height if you live in a region where the climate gets very hot. This way, you’ll be able to protect the tomatoes from the harsh heat. Remember that while tomatoes hate icy conditions, uncontrolled high heat can also be detrimental to their growth.
Ideal Humidity To Grow Tomatoes In A Greenhouse
The ideal humidity to grow tomatoes in a polytunnel is between 60 to 70 per cent. Keeping your polytunnel humidity in this range will help you prevent mould growth and other diseases. Humidity also plays a role in regulating the polytunnel temperatures, so check your ventilation system regularly.
Ventilation is especially essential during cool, cloudy mornings. Drying the plants by heating or ventilating will control leaf mould and replenish the carbon dioxide that the plants need. And lastly, proper control of humidity can help reduce heating and cooling costs on your part.
How Do You Grow Tomatoes In A Polytunnel Year-Round
You can grow tomatoes in a polytunnel year-round if you consider the tomato variety, season, feeding, and watering beforehand. Unlike with field growing, using a polytunnel can extend the growing season of your tomatoes. However, failing to execute a plan according to these factors will give you a hard time achieving a year-round production.
Tomato variety
Similar to when you’re growing tomatoes outdoors, you have to know what varieties would be suitable in an indoor environment. It sounds complicated, but it’s as simple as choosing the seeds marked as “greenhouse variants.” They are so-called because they built to tolerate the conditions indoors instead of your typical UK garden varieties.
For greenhouses, you want vine or cordon tomatoes. The most popular and widely-used indoor tomato variety in the United Kingdom is called Trust. There are also Dutch hybrids called Match, Switch, and Blitz that are all worthy considerations for indoor growing.
How long will a tomato plant live in a greenhouse
A tomato plant will live in a polytunnel for years as long as the conditions are ideal. The reason behind this indefinite lifespan is because polytunnel varieties of tomatoes are indeterminate, so they continuously produce flowers and fruits as they grow. They can grow several meters long and can have over a long harvest season.
Season
Growing tomatoes in a field meant planting the seeds before the last frost of the year. But with polytunnel tomatoes, you can seed an autumn crop and a spring crop in early June and December, respectively. Depending on the location, you can have up to two tomato crops during the year, as long as you maintain ideal conditions inside.
Can you grow tomatoes in a polytunnel in winter
You can grow tomatoes in a polytunnel in winter because greenhouses can trap the heat from the sun’s radiation and then keep it inside. However, be aware that the heat inside is only relative to how cold it is outside. The solution is supplementing heat, and you’ll still be able to experience an increase in yield with your polytunnel tomatoes during winter.
When can tomatoes go in an unheated greenhouse
You can plant tomatoes in your unheated polytunnel after the last frost date has passed. Why after the later frost date? Any temperature lower than 50°F will affect the germination and growth of your seeds.
It would help if you waited until your UK region’s last frost date has passed to ensure good outcomes. Unlike in a heated greenhouse, your tomatoes are more at risk of the damages caused by environmental changes. Therefore, knowledge of your UK region’s condition and timing are essential for success.
Feeding
Once you transplant the tomatoes into their final pot, you can start fertilising. How often do you feed tomatoes in a greenhouse? Feed your growing tomatoes every one or two weeks with a nitrogen-rich liquid fertiliser.
Once you see fruits, you can switch to using a tomato fertiliser. Remember to follow the instructions of the fertiliser to know how often you should feed your plants. You also want to skip feeding twice during the tomato plant’s life cycle if you use liquid fertiliser to prevent the accumulation of salts.
Watering
Apolytunneltomato plant requires up to 3 quarts of water per day. Make sure you’re watering your plants at regular intervals, and it can be more often in a hotter climate. However, do note that tomato leaves are sensitive, so avoid using overhead irrigation for watering.
You’ll know that your plants are not getting enough water if their leaves are wilted and dark green. On the contrary, yellow leaves mean that you are overwatering your tomatoes. Make sure the soil of your plants is moist and not dry or soggy.
Do Tomatoes Grow Better In A Greenhouse
Tomatoes grow better in polytunnel because of the extension of the growing season, protection against temperature and weather changes, and a safe growing environment. Polytunnel tomato farming has been rising since the mid-1990s because these advantages solve the quality inconsistencies in field tomato farming. As a result, consumers also had an increasing preference for polytunnel tomatoes.
Extension of the growing season
Tomatoes can be picky plants, so it’s typical for field growers to have a shorter growing season depending on their UK region. Using a polytunnel eliminates this drawback because you don’t have to stop growing your tomatoes once the summer months are over. Growing tomatoes in the polytunnel give you the advantage of extending your harvest season until late autumn.
Protection against temperature and weather changes
Growing tomatoes indoors will protect the plants from the erratic temperature and weather changes outside. Infield farming in the UK, you have no control over the harsh heat, wetness from rain, and fluctuations in temperature. As a result, the tomatoes become more vulnerable to diseases and other conditions when they’re outside.
Safe growing environment
Besides protection from temperature and weather changes, the polytunnel also makes a safe growing environment for the tomatoes. Its structure will make it impossible for predators like birds, rodents, and large mammals to access the plants. The enclosed environment will also deter anyone from causing potential damages to your crops.
Bottom Line
The ideal temperature to grow tomatoes in a polytunnel is between 70°F to 80°F during daytime and between 60°F to 65°F during nighttime. On the day, it’s best to stick to the low end of the range when it’s cloudy and then use the temperature at the high end if the weather is clear. These adjustments ensure that your tomatoes will be able to photosynthesise efficiently, regardless of the condition.
Maintaining your polytunnel temperature in these ranges from daytime to nighttime is crucial for your tomatoes’ growth and health. If the polytunnel temperature gets too high, the fruits and root growth will be affected. On the other hand, letting the polytunnel temperature get too low puts your tomato plants at risk for nutrient deficiencies and fungal infections.
Using a thermostat, effective ventilation system, alternate heating system, evaporative cooling system, and modifying the polytunnel roof are the ways to maintain the greenhouse’s ideal temperatures. Simultaneously, you must monitor the polytunnel humidity because it plays a significant role in regulating the polytunnel emperature.