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The ideal greenhouse temperature and humidity settings for every season

How to get the right temperature and humidity level for healthy plants

A small greenhouse with tiered shelves and tall plants are growing in it
Michelle_Raponi / Pixabay

Everyone wishes they could grow their favorite plants and vegetables year-round, but the changing seasons make that impossible outside. Greenhouses can help by providing a sheltered and controlled environment for your plants. If you’re new to greenhouse gardening, then the extra control greenhouses provide might be overwhelming. Now that you’re in complete control of the temperature and humidity surrounding your plants, what is the best environment for your plants?

Whether you are growing vegetables year-round, or simply plants that look beautiful, there are steps you can take to support your plants’ growth. Here’s everything you need to know to control your greenhouse temperature and humidity levels so that your plants can thrive.

Exterior of greenhouse on concrete patio
Semmick Photo / Shutterstock

The perfect temperature and humidity

While each plant is different, the ideal greenhouse temperature for most plants and vegetables is 80 degrees Fahrenheit. or 27 Celsius. Most plants will grow healthily in this temperature. For humidity, the higher the temperature, the higher the humidity you want. The chart below provides the ideal greenhouse temperature and humidity comparisons:

°F Humidity
50° 83%
61° 89%
68° 91%
86° 95%

However, 80 degrees Fahrenheit. is simply a general guideline. You should look up the ideal temperature for each of your plants if you are worried about disease or infection. For example, if you are growing crops that love a ton of sun, such as tomatoes or melons, then your temperature should be warmer. In general, do not rise above 90 degrees Fahrenheit (32 Celsius) and do not fall below 75 degrees Fahrenheit. (24 Celsius). Sticking in this range will keep most plants alive and healthy.

The proper temperature must be maintained because these plants are growing in an artificial setting. In such a setting, the temperature and humidity can increase quickly, especially if you have a lot of plants. Thankfully, there are many ways to control the temperature so your plants thrive.

greenhouse in winter
flora Asadi / Shutterstock

Controlling the temperature and humidity

The temperature in a greenhouse is driven by the amount of sunshine and ventilation. The point of greenhouses is to trap the sun’s heat; while that makes it easy to get a hot room, it does not make it easy to control that heat. However, there are a few simple ways to moderate the temperature and humidity.

The biggest thing to create is ventilation. While that could mean installing vents in the roof, it could also simply mean opening windows and doors to create a cross breeze. You could also use air conditioning to bring the temperature down. During the winter season, pull in the cold air and exhaust the warm air with fans to reduce the humidity.

Depending on what you are growing, you can even trick the plants into thinking they are in a different season. Extra grow lights can imitate the sun during the winter while heaters can increase the temperature. However, this can be set up to be almost fully automatic using greenhouse timers. This brings us to the tools you can use for proper greenhouse temperature and humidity monitoring.

Annie Spratt / Unsplash

Tools for greenhouse monitoring

There are great tools for a greenhouse that can easily maintain it. While these devices are not necessary, greenhouses are artificial settings that need proper maintenance and care at all times, especially during the off-season. These tools make that much easier.

Greenhouse temperature alarm

This alarm tracks potential problems in the greenhouse, such as power outages, temperature fluctuations, water damage, and bug intrusion. Some models go one step further and will send you a text message of any such occurrence.

Greenhouse temperature control system

This tool provides proper and dependable heating and cooling options for your greenhouse. Keeping the temperature at an optimum level year-round is important. Despite the outside weather, you can maintain the temperature to whatever is needed.

Greenhouse temperature sensors

One of the coolest things (no pun intended) about greenhouses is the chance to automate them. Sensors monitor the temperature in the greenhouse and can automatically activate vented roofs, side vents, and fans to keep the temperature at the optimum level. Some sensor models can also alert you if these systems stop running or run into a problem.

Remote temperature monitor

Keeping track of the greenhouse temperature throughout the day is very important. How can you know how to grow your plants without an accurate reading of how hot it is throughout the day? A temperature monitor lets you see broad data about the temperature over a defined period of time. The temperature is recorded so you can view it at any moment.

Small rounded greenhouse
Grundsteins / Shutterstock

Does location impact greenhouse temperature and humidity?

Yes! Both the location of the greenhouse in your yard and where you live in the world can impact the temperature and humidity in your greenhouse. For example, someone with a greenhouse who lives in Florida, where it is hot and humid for most of the year, will have a naturally hotter and more humid greenhouse, and may have a harder time cooling their greenhouse off.

Additionally, a greenhouse in full sun will stay warmer throughout the year than a greenhouse place in mixed sun and shade. A greenhouse in full shade will stay much cooler, which is why it is typically not recommended for greenhouses to be placed in full shade (plus your plants might not get enough light).

Keeping optimal temperatures and humidity is very important for keeping your plants healthy. While it depends on which vegetables and plants you are growing, there are tools and tips anyone can implement to increase their chances of growing crops year-round, automatic and (almost) hassle-free.

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You may be wondering if you even need to worry about cleaning your greenhouse. If you don't mind the dirty look, maybe you could leave it as it is? Unfortunately, it's much better for your greenhouse and your plants if you give the greenhouse a deep clean at least once a year. It'll make it easier to use when it is clean and organized, and the walls of the greenhouse need to be clear so they can let in as much light as possible. Additionally, a clean greenhouse is less likely to spread pests and diseases to your precious plants. And lastly, things last longer when you care for them and greenhouses aren't cheap.

When should you clean a greenhouse?
There's no right time to clean a greenhouse; whenever you can is better than not at all. However, we suggest cleaning it when there isn't so much to do in the garden and it isn't so hot out. Usually, the fall is when the garden chores slow down and it starts to cool out, making cleaning the greenhouse much easier on you.
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Step one: Empty the space
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Step two: Rough dusting
Over the season, spiders and bugs and maybe even some mice have tried to make homes in your greenhouse. This has probably led to a few cobwebs and dust piles around the corners. You'll want to remove these large areas of debris before you start the deep cleaning. Use a broom to knock down the cobwebs and sweep up the floor; you've probably spilled some soil during the summer!
Step three: Clean the walls
The panels of your greenhouse will now need to be deep cleaned. You can use a bucket of warm water and a sponge to wipe them down, but we also recommend bringing a long-handled brush to make life easier. This way, you can dip the brush into the bucket of soapy water and scrub down the walls with the long-handled brush. You'll be able to reach every inch of the walls without killing your back.

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There's a time in every gardener's life when they try to grow their own veggie plants from seed. This is a gratifying process, and there are many benefits to growing your own seed starts. One of those benefits is bigger and healthier plants. By growing your own baby tomato plants, you can ensure that the plants are well cared for, never given anything you don't want them to have, and transplanted in just the right way at just the right time for optimal plant health. So how do you transplant tomato plants to ensure they're happy and healthy and live to produce lots of yummy tomatoes for your home?

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Step one: Harden the plants
Hardening the plants is a term gardeners use when talking about the process of acclimating a greenhouse-grown plant to outside conditions. Typically it refers to sunlight, but it could also refer to wind and other weather that could harm the plant. About a week before you're ready to transplant, you'll want to harden your baby tomato plants by exposing them to sunlight at increasing increments each day. For example, day one should be about 30 minutes, then 45, then 50, and so on until the day of transplanting. If you don't do this, you'll risk your plant being burnt and killed when you transplant it outside.
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Step three: Prepare the new soil
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Can you have an indoor greenhouse?
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