Greenhouses can get very hot during the summer, so it is important to make sure the temperature does not get so high that it causes damage to the plants. Ventilation and shading the greenhouse, as well as keeping the floor moist, are easy ways to prevent extreme heat from damaging the plants.
Even heat-loving plants can suffer when temperatures get too high, above 80°F. Heat stress can cause wilting, defoliation, and leaf burn, and flowering and fruit set can be significantly affected.
If you're growing anything in a greenhouse, pay close attention to the weather forecast and monitor the temperatures. In addition to keeping your plants hydrated by watering them, protecting them from environmental factors like extreme heat will help them thrive. Thankfully, there are quick and easy ways to control humidity in a greenhouse.
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Conservatory moisture management – focus
As a professional gardener, I have worked in greenhouses for many years – large greenhouses specialized in plant propagation, and production greenhouses growing tomatoes, peppers, eggplants, and other heat loving crops. I have worked in greenhouses all year round and used damping down to cool the high temperatures. I have also spoken to greenhouse experts about the benefits of damping down and how to do it.
Benefits of moisture control in greenhouses
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Lowering the temperature inside a greenhouse is an effective way to cool it down, especially when temperatures rise in the summer.
Along with ventilating a greenhouse in the summer, it can also be beneficial to cool the greenhouse to prevent the plants from suffering from excessive humidity. I have worked in greenhouses in the summer and have experienced the cooling effect that can be achieved by keeping out moisture.
“The main goal of moisture control in a greenhouse is to reduce the temperature inside the greenhouse through ‘evaporative cooling’ – the evaporation of water cools the air to a comfortable temperature,” says Lucie Bradley of Two Wests & Elliott.
“It's one of the simplest, easiest and most economical ways to lower the temperature in a greenhouse.”
Reducing humidity is also a practical way to increase humidity in a greenhouse, which will help prevent plants from becoming heat stressed.
Sarah Warner, greenhouse manager at Case Western Reserve University Farm, says increased humidity can help plants develop, adding: “If humidity levels drop below 60 percent at night and 80 percent during the day, plants may grow slower than normal.”
Keeping a greenhouse cool and moist will also help prevent pests and diseases that thrive in dry environments, such as spider mites and powdery mildew.
Lucy Bradley
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Greenhouse Expert
Lucy has worked for Two Wests & Elliott since 1997, a company specialising in greenhouse equipment, garden tools and a range of horticultural products. She started out working alongside the founders, Mr and Mrs West, until they retired and is now fortunate to be one of the co-owners. She also enjoys the opportunity to speak to customers every day, both amateur and professional gardeners, and is constantly learning.
Sarah Warner
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Greenhouse Manager
Sarah Warner is a farm associate with the Farm Foods Program at Case Western Reserve University Farm. She graduated from Lorain County Community College with an Associate's Degree in Sustainable Agriculture and is certified in Permaculture Design.
How to reduce humidity in a greenhouse
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Dehumidifying the greenhouse can be a quick and easy task that can be done as part of planning the greenhouse activities for the day. On hot, dry days when temperatures in the greenhouse exceed 68°F, it can be beneficial to be proactive and employ cooling techniques, as temperatures above 80°F can cause damage to plants.
Using a bucket, watering can, or garden hose, water all hard surfaces in the greenhouse, primarily the floor and walkways, but also any shelves or staging. Allow the water to dry naturally and it will cool the air as it evaporates.
Be careful not to pour too much water on the leaves and fruit in the greenhouse, as excess moisture on the plants increases the risk of fungal diseases. If you are growing plants in ground-level flower beds along walkways, be careful not to flood the flower beds, as this can overwater the plants.
Moistening can be done at any time of the day, but the ideal time is early in the morning: “Water evaporates slowly during the day, creating enough humidity in the air to help prevent your plants from becoming heat stressed,” explains Lucy.
“Depending on the temperature on a dry summer day, it may be necessary to dehumidify the greenhouse up to three times a day: early in the morning, late in the evening (right after the greenhouse is ‘closed’ for the day), and midday.”
Greenhouse doors and windows should be left open during the day to keep moisture out, cool the temperature and allow air to flow.
Bluetooth Hygrometer Thermometer
Monitor the temperature and humidity in your greenhouse and receive instant alerts if the temperature or humidity goes outside of your pre-set ranges.
This metal waterer holds one gallon of water and has a removable spout and two handles, making it easy to use outdoors or in a greenhouse.
This lightweight garden hose expands to 100 feet in seconds under pressure and has 8 different spray patterns to handle any watering job.
FAQ
Should I open the greenhouse every day?
On warm, sunny days, it is important to open the doors and vents of your backyard greenhouse to help cool the temperature. During the hottest months, you may want to leave the doors and vents open overnight if temperatures remain high.
Open the greenhouse only when the temperatures rise. Leaving doors or vents open on cold days can allow the temperature to drop or allow cold drafts to blow in that can harm the plants.
Using a digital thermometer to track the temperature throughout the day and night can help you make an informed decision about when to open your greenhouse.
It's so simple and effective, which is why humidity control in a greenhouse should be on your summer gardening checklist. Whether you're growing vegetables, flowers, or tropical plants in your greenhouse, humidity control in the beds when temperatures rise will keep your plants healthy and protect them from heat stress.