Greenhouses require growers to maintain a stable and favorable environment for plants to thrive.
One of the most important conditions is temperature. At times, however, greenhouses tend to get cold at night.
Greenhouses Get Cold at Night
Greenhouses require a constant temperature of between 80 and 85 degrees Fahrenheit for optimum growth and development of plants. During the night, temperatures usually drop outside. This causes the temperature in the greenhouse to drop too, by about 20-30°F.
How Cold Is Too Cold for a Greenhouse?
Before we can define what “cold” is in a greenhouse, we need to understand that it’s all tied to the use of the greenhouse.
A greenhouse can be operated as a hothouse, a cool house, or both. It all depends on how you use it throughout the year.
To this end, a hothouse requires temperatures to be maintained at 55 degrees Fahrenheit or more, while a cool house requires the minimum temperature to be 45 degrees Fahrenheit.
So with this in mind, it’s safe to say that any temperatures below 55 degrees Fahrenheit for a hothouse and below 45 degrees Fahrenheit for a cold house can be termed as “too cold for a greenhouse.”
To maintain these temperatures, there must be a way to heat your greenhouse when it gets too cold.
The level of cold that your greenhouse crops can withstand also differs. Greenhouse crops can be broken down into three basic categories depending on their base temperatures:
- Cold tolerant crops – These crops have a base temperature of 39 degrees Fahrenheit or lower.
- Cold-temperate crops – These have a base temperature of between 40 and 45 degrees Fahrenheit.
- Cold-sensitive crops – These have a base temperature of 46 degrees Fahrenheit or higher.
Base temperature (otherwise known as minimum temperature) is the coldest temperature when a plant doesn’t develop. At or below the base temperature, plants don’t grow leaves, and they don’t flower.
Therefore, you need to consider the base temperature of your greenhouse crops to determine their desirable growing temperatures and maintain this in your greenhouse.
Of equal importance and worth you knowing is the optimum temperature of your greenhouse crops. This is the temperature at which plant development is most rapid.
This temperature varies from crop to crop and is usually between 70 and 90 degrees Fahrenheit. It’s important to keep the temperatures in your greenhouse in this range for optimum plant development.
For you to start experiencing freezing air temperatures in the greenhouse, it needs to get below zero degrees Fahrenheit outside.
How Much Warmer Is an Unheated Greenhouse at Night?
An unheated greenhouse, otherwise known as a cold greenhouse, is heated only by the sun.
The difference in temperature inside an unheated greenhouse compared to the outside can be up to 30 degrees Fahrenheit.
The extent of this variation usually depends on the type of greenhouse you have and the degree of insulation in your greenhouse.
A single-layer greenhouse usually has a temperature difference of about 5 to 10 degrees Fahrenheit.
A double-layer greenhouse will usually have a temperature difference of around 9 to 14 degrees Fahrenheit compared to the outside.
How Cold Do Greenhouses Get at Night?
In the Northern US, the temperatures in greenhouses can drop to between 50 and 60 degrees Fahrenheit at night.
However, in the winter, the greenhouse temperatures can be as low as 0 degrees Fahrenheit at night.
Greenhouse temperatures can get to between 60 and 70 degrees Fahrenheit in the South, especially on summer nights. In the winter, greenhouse temperatures can drop to below 15 degrees Fahrenheit at night.
In the Mid US, greenhouse temperatures can get to between 40 and 50 degrees Fahrenheit at night. In the winter, greenhouse temperatures can drop to below 10 degrees Fahrenheit at night.
Do People Normally Heat Greenhouses?
During cold weather, especially in the winter and cold nights, the greenhouse temperatures can fall drastically.
Cold temperatures can negatively impact the development of plants in the greenhouse by causing stunted growth. In extreme cases, plants may die eventually.
For most growers, it is essential to maintain a constant temperature of about 80 to 85 degrees Fahrenheit. That’s why people will heat greenhouses when it gets too cold.
For more information, check out our article: Greenhouses & Electricity: 5 Questions Answered (for Beginners)!
Should I Make My Greenhouse Airtight To Preserve Heat?
Greenhouses need to be air-tight. If they are not air-tight during colder months, the heat inside the greenhouse will leak out, and cold air will leak in, causing the temperatures inside the greenhouse to fall.
So you should make sure that your greenhouse is air-tight. This will keep in heat and preserve it so that your greenhouse doesn’t get too cold for the plants.
So yes! It would be best if you made your greenhouse air-tight to preserve heat.
How Can You Heat a Greenhouse Without Electricity?
Running electric heaters in your greenhouse can significantly raise your energy bill.
For the majority of growers, it’s not economical to heat their greenhouse with electricity. This is because the electric costs can sometimes be higher than the value of the plants.
Luckily, it’s possible to heat your greenhouse without having to add to your energy bill. Here are a few tips on how to heat your greenhouse without electricity.
1. Using Compost
Compost is one of the best ways to generate heat.
A compost pile can generate nearly 160 degrees Fahrenheit. This means that compost can be an effective way to heat your greenhouse. You also get the added advantage of making the soil fertile.
You can compost anything that can decompose, including hay, plant clippings, and leaves.
To heat your greenhouse using compost, place it in the middle.
Microorganisms will break down the organic material in the compost to release energy in the form of heat.
2. Using Solar Heaters
Another ingenious way of heating your greenhouse without using electricity is using solar heaters.
All you’ll need is a heater, solar panels, and rechargeable batteries.
Solar panels absorb energy from the sun and convert it to electricity which will run your solar heater. Having rechargeable batteries will enable you to store energy for use when there is no sunlight.
3. Shared Heat
Another creative idea for heating your greenhouse without electricity involves the concept of shared heat.
This involves constructing your greenhouse against a building with which it can exchange heat. An example of such a building is a chicken coop.
The heat produced by the chicken in the shared building will heat your greenhouse, keeping the temperatures favorable.
4. Thermal Mass
Thermal mass acts as a battery for heat.
Essentially, during warm periods like sunny days, the thermal mass heats up, and when it gets cooler, the thermal mass will slowly release the stored heat.
Thermal mass can be anything from water barrels, stones, paving bricks, or straw. Anything heavy and dark can be an excellent thermal mass. Such materials work best to capture, retain, and slowly release heat.
The best thermal mass choice is water barrels. This is because water has a higher heat capacity and will therefore effectively heat your greenhouse.
Dark stones are also ideal since they will heat up from the sun and provide a steady heat release when it gets cold in your greenhouse.
Therefore, it would be best to consider adding some form of thermal mass in your greenhouse. This will heat your greenhouse without having to use electricity.
5. Sink your Greenhouse
Most people consider basements to be dingy, cold places.
The truth, however, is that the underground is often warmer than above ground. The deeper in the ground it is, the more constant the temperature becomes.
So if you’d like to keep your greenhouse warm, consider sinking the floor of your greenhouse below the frost line.
This way, the warmer earth will help moderate the temperature inside your greenhouse by providing additional heat.
Insulation is an ideal way of keeping in the heat in your greenhouse and reducing the need for electricity to heat your greenhouse.
The most common insulation materials in your greenhouse are bubble wrap, glass, and greenhouse plastic.
All the above insulation materials can be effective in trapping heat in your greenhouse. Consider using two forms of insulation, such as plastic for the exterior and then bubble wrap for your greenhouse interior.
If you decide to use one insulation material, it’s advisable to go with bubble wrap, especially for greenhouses. It lasts longer- about three years.
When insulating your greenhouse, make sure you leave no gaps between insulation layers and edges.
All in all, you should always ensure that the temperature in your greenhouse is maintained at the optimum level, which is neither too cold nor too hot.
This will ensure that the plants grow and develop well.