Growing anything in the greenhouse in cold conditions may seem almost impossible.
Frost can damage plants that are not hardy.
This is especially the case for growers unaware of the steps they can take to prevent frost from ruining their plants.
Luckily though, greenhouses can help protect against damage by frost:
Here’s How Greenhouses Protect From Frost
Greenhouses are made of plastic or glass walls that allow the sun’s rays to enter the structure and raise the air temperature while keeping this warm air from escaping. When it gets too cold outside, this warm air keeps the greenhouse safe from frost.
At What Temperature Do Greenhouses Freeze?
Greenhouses begin to freeze when the temperatures drop below 30 degrees Fahrenheit and remain at that temperature for long.
At this temperature, the plants start to freeze, and in extreme cases, the plants end up dying.
Is an Unheated Greenhouse Frost Free?
An unheated greenhouse can keep temperatures as much as 30 degrees Fahrenheit warmer than outside.
This can keep greenhouse plants frost-free in all but the very worst of winters.
With insulation, your greenhouse’s internal temperature can be as high as 41 degrees Fahrenheit higher than the outside.
So to give your unheated greenhouse the best chance at being frost-free, insulation can come in handy.
When Should You Heat Your Greenhouse?
Sufficient heat is essential in greenhouses since it provides your plants with a controlled environment suitable for plant growth and development.
Without sufficient heat, your plants will have stunted growth and may even end up dying.
That’s why it’s important to heat your greenhouse when temperatures get too low (often below 40 degrees Fahrenheit). Therefore, there are two instances when you should heat your greenhouse:
1. During cold nights
The temperature in the greenhouse should be 75 degrees Fahrenheit at night.
During some nights, temperatures can drop to as low as 20 degrees Fahrenheit.
While there may be plenty of sun during the day, greenhouses (especially uninsulated ones) will cool off quickly at night.
2. During the winter
Depending on where you live, winters can sometimes be harsh environments and extremely cold.
Temperatures during winter have been known to drop to below 0 degrees Fahrenheit.
This, therefore, means that you need to heat your greenhouse so that the cold weather doesn’t affect the internal temperature of your greenhouse.
It’s advisable to get a thermostat for your greenhouse. The thermostat will help you monitor the temperatures so that when it gets too cold for your plants, you know when to heat your greenhouse.
What Temperature Is Too Cold for a Greenhouse?
The ideal temperature inside a greenhouse is usually about 80 to 85 degrees Fahrenheit.
Keeping this internal temperature steady is one of the most important parts of owning and operating a greenhouse. A greenhouse can either be operated as a cool house or a hothouse.
A hothouse requires a minimum of 55 degrees Fahrenheit, and a cool house should have a minimum of 45 degrees Fahrenheit.
So any temperature below these can be considered too cold.
Another factor worth considering is the base temperature of the greenhouse crops. The base temperature is the coldest temperature at which a plant cannot develop.
Therefore, a greenhouse can be termed too cold when the temperature falls to or below your greenhouse plants’ base temperature:
- Cold tolerant crops have a base temperature of 39 degrees Fahrenheit or lower.
- Cold temperate crops have a base temperature of between 40 and 45 degrees Fahrenheit.
- Cold sensitive crops have a base temperature of 46 degrees Fahrenheit or higher.
7 Ways To Frost Protect Your Greenhouse
Depending on where you live and how severe the winter is, you may need to think about heating your greenhouse.
It may not be the most glamorous job but protecting your greenhouse from frost is an important undertaking. Protecting your greenhouse from frost will give your plants the best chance at survival.
Failing to protect your greenhouse from frost may cause stunted growth in your plants and even death.
Keeping your greenhouse as small as possible can help since smaller spaces heat up quicker than large ones. There are, however, several other things you can do to keep out frost.
1. Use Heat Absorbing Rocks
To keep out frost, you should build your greenhouse over a large natural rock.
Alternatively, if you already have a built greenhouse, you can place a large, dark rock in your greenhouse.
Rocks are good thermal absorbers, and on sunny days, they will absorb heat from the sun and radiate it within your greenhouse.
This will significantly raise the temperature in your greenhouse and protect it from frost.
2. Insulate your Greenhouse
One way you can prevent frost in your greenhouse is to insulate it thoroughly.
This will ensure that all the heat in your greenhouse doesn’t escape leaving it prone to freezing and frost.
Most of the heat loss in any room occurs using conduction through the windows and poorly insulated walls. So to prevent heat loss in your greenhouse, the walls, as well as windows, have to be properly insulated.
You can use bubble wrap specifically meant for greenhouses for insulation purposes. It acts as double glazing and effectively keeps the cold out of your greenhouse.
This protects it from frost.
3. Add a Heater
An effective way to keep out frost in your greenhouse is to add a heater.
A heater will raise your greenhouse temperatures whenever they get too low, thus eliminating the chances of frost formation.
You can use electric heaters or solar heaters if you are energy conscious.
Make sure to keep the heater away from flammable materials and make sure that you install it correctly, relative to your greenhouse size.
4. Use Compost
Not many people know this, but compost can produce temperatures as high as 160 degrees Fahrenheit.
So during freezing winters, compost can come in handy to protect your greenhouse from frost.
Working compost raises the general temperature of your greenhouse as well as the temperature of the soil. In addition to this, it provides manure to your plants by providing nutrients to the soil.
5. Use Thermal Mass
Thermal mass can be anything from stones, water barrels, paving bricks, and straw.
During sunny days, the thermal mass heats up, and when it gets cooler, the thermal mass will slowly release stored heat. This will ensure that your greenhouse temperatures don’t fall so low that frost begins to form.
The best thermal mass is water since it has a higher heat capacity.
So consider having several water barrels in your greenhouse to aid with this.
6. Use Frost Protection Fleece
When the temperatures outside get too cold, place a layer or two of frost protection fleece over your greenhouse plants.
This will give them several degrees of protection from the cold. They will retain the heat within your greenhouse.
Don’t forget to remove the fleece to ensure your plants get adequate light and ventilation during the day.
7. Construct Raised Garden Beds
Your greenhouse plants should have deep, raised beds.
Raised beds that are filled with rich, dark soil usually warm better than smaller and flatbeds. Raised beds also hold heat longer.
By building raised beds for your plants, you ensure that frost doesn’t form and spread quickly on the soil in your greenhouse.
In conclusion, even if your greenhouse is unheated, follow the tips above to ensure the conditions are just right for your plants to flourish.