When Can I Put Plants in An Unheated Greenhouse?

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If you’re looking to prolong your plant’s life and continue growing them throughout the winter months, you probably want to tuck them away inside of a greenhouse. Frost can be highly damaging to plants, as it’ll freeze and expand in their cells. Because of this, the cell walls break. Meaning vital nutrients (sap) can no longer be held within them, causing the plant to die. To massively reduce the chances of this happening, you’ll want to ensure your plants don’t go below freezing temperatures. One way to do this is through an unheated greenhouse, but when should you put your plants in there?

The perfect time to put your plants inside an unheated greenhouse is four to six weeks before the average first frost date. This widely varies on the country you live in. For example, the United States average frost dates range from the 25th of August to the 13th of December, depending on which zone you live in. 

Remember, average frost dates should be taken with a pinch of salt. If your area or “zone” experiences frost before the expected dates, it might be ideal to start moving your beloved plants inside of your greenhouse. From being prepared, you’ll minimize the risk of your plants potentially becoming damaged from frost.  

In this article, we’re going to discuss more about the purpose of a greenhouse, how to prepare one, and various helpful tips to ensure your plants are safe during the colder months.

How to Prepare Your Unheated Greenhouse for Winter  

The whole concept of growing or maintaining plants in a controlled environment, like a greenhouse, stems from Roman times. Since the idea was invented, it’s proven itself to be excellent. Especially unheated greenhouses as these are cost-effective and healthy for our planet.

However, through trial-and-error various winter preparation tactics have shined above all. To winterize your unheated greenhouse correctly, see the below suggestions.  

1.Have a cleanup

Let’s be honest here. Not many people are a fan of cleaning, but it’s essential for your greenhouse before you head into winter. Throughout the year, your greenhouse will encounter an abundance of different weather seasons. This may cause the glass panes to become stained and turn green.

As we’re aware, light is an essential factor in a plant’s growth and health. By doing this, you’ll ensure that your greenhouse is gaining the most amount of natural heat from the sun.

2.Prepare your soil

If you are repotting any plants, you might want to prepare your potting mix to guarantee it has the correct soil pH and acidity. Most plants grow in alkaline soil, but several plant families prefer acidic soil, such as Ericaceae’s. Supplying your plants with the correct soil will enhance their growth and enormously reduce the chances of them dying.

3.Insulate your greenhouse

Glass greenhouses are known to be very sensitive to frost in the winter months. Although it captures and stores heat from sunlight during the day, it can become significantly colder at night. Experts recommend lining it with bubble wrap if there are signs of frost building up in your greenhouse during the night.

First, line the inside and monitor the protectiveness. If you see frost appearing again, for added reinsurance, add another layer of bubble wrap to the outside of your greenhouse and fix it down appropriately.

Alternatively, you could also use plant covers to increase the possibilities of your plants surviving winter.

4.Think, location

Before putting anything in your unheated greenhouse, you need to think about its current location. As it’s unheated, you’ll need to identify a place in your backyard that receives the most amount of sunlight during the winter months. The primary source of heat will, of course, be the sun. So, you’ll want to maximize the potential sunlight your greenhouse receives.  

As you’re able to grasp from the above, preparing your greenhouse for winter isn’t rocket science. But from organizing the above before you put your plants in there will immensely increase their chances of survival during these cold months.  

How Cold Can Plants Tolerate in A Greenhouse

If you want to take extra caution in preventing your plants from dying once you’ve transferred them into your greenhouse, many people use garden thermometers to track the temperature. By understanding this, you’re able to act on the situation accordingly.

All species of plants have a different temperature threshold than one another. However, as a rule of thumb, you should follow this guidance:

Tropical plants – Typically, plants that are considered exotic or tropical tend to react with cold weather much worse than any other plant groups. Most tropical plants will keel over when temperatures fall below 40°F to 35°F.

Non-tropical plants – If you’re putting non-tropical plants inside of your greenhouse, as a guide, you should try to keep the temperature above 18°F to 20°F.

Remember, all plant species react differently to cold weather. To amplify the chances of your plants surviving winter, you should gather information either through a garden book or online resources to get exact temperature guidance.

After checking the temperature of your greenhouse, if it’s below the recommended requirement, I suggest you use one of the above insulation techniques. Using bubble wrap or plant covers can ensure your cherished plants won’t die from frost.  

Can heat cause problems to plants?

When we’re exiting the colder months and entering into the warmer ones, you must remove your plants at the appropriate time. Like with cold weather, plants can become highly damaged if they’re sitting in a hot environment for an extended period of time.

Tropical-like plants can withstand these temperatures much better. But typical “non-tropical” plants can start dying from temperatures of 81°F and up. During the build-up to summer, the likelihood of your greenhouse exceeding these temperatures is pretty standard. Be sure to keep an eye on your greenhouse’s temperature and act appropriately with the situation.  

Why You Should Use an Unheated Greenhouse

After reading the above, you should be aware of the importance of putting your plants in a greenhouse during the winter months. If you want to prolong their lives and increase the chances of them growing into something spectacular, it’s vital to imitate their ideal environment all year round. The best way to achieve this is by using an unheated greenhouse. But apart from this, why else should you use one?

Multipurpose usage  

Having the right tools are essential for every gardener, and an unheated greenhouse can be another prestigious item to add to the collection. With an unheated greenhouse, you’re able to use it for many gardening activities. It can be used as a designated area for plant and vegetable cultivation, or a complete storage area for all your gardening needs.

From having your gardening equipment, plants, and vegetables located in the same area makes for much easier access. Which ultimately leads to better care and results from your gardening efforts.

Easier to regulate

Because of this designated area, you’re able to monitor and regulate growing conditions that can seem problematic with a whole backyard. Within a greenhouse, you’ll have flower beds or pots. By having these small, assigned areas for specific plants or plant species, you can control the soil’s pH levels and acidity to maximize a plant’s growing capabilities.

Apart from providing these types of “perfect” growing conditions, you can also dramatically reduce the chances of pests destroying your plants. By having an enclosed environment, it acts as an extra barrier of protection from the outside world.

Increases plant availability

Most places dotted around the world will have better environments for growing specific types of plants. Having a walled area suitable for growing crops or plants can increase the versatility of plants you’re able to grow in your backyard.

For example, in some climates in the United States, you won’t be able to grow exotic plants in your ordinary backyard successfully. To counteract this issue, you’re able to use a greenhouse. Because you can somewhat control and monitor the temperature, it massively increases what you’re able to grow all year around.

Great for the environment

As you can probably imagine, an unheated greenhouse is great for the environment. It requires no electric or gas heating and just renews the energy from the sun each day. Most of the time, it’s also made from plastic or glass, which doesn’t destroy the natural beauty around it—making it the ideal storage or cultivating area for your gardening.

Ultimate weather protection

From reading the above, you should understand that greenhouses protect our plants from frost damage. But this isn’t the only weather a greenhouse can help protect your valuable plants. The adaptability of a greenhouse continues as you’re able to save your plants from heavy down poor, extreme winds and even intense sun rays if you cover it.  

Saves you money

Of course, by increasing this type of controlled climate, you’re able to grow fruit and veg all year round. By offering this, you’ll reduce your weekly shopping bill for these specific groceries. It also goes without saying, the longer you can keep your plants alive, the less likely you’ll need to purchase them again.

Above are some great benefits that every gardener will adore to obtain. They’re also relatively affordable for what you’re able to achieve from them. Typically, plastic greenhouses can start anywhere from $70 depending on your requirements, making it a cheap garden upgrade anyone can accomplish.

Can You Grow All-Year-Round in A Greenhouse?

Typically, people use greenhouses to store plants and grow vegetables throughout the colder months. It can be challenging to determine whether or not you should start growing a particular type of vegetable for any beginner.

For maximum efficiency from your greenhouse, you should consider growing the below depending on the season.

Winter to Spring

  • Plant/sow hardy plants like broccoli, brussels sprouts, cabbage, leeks, lettuce, and onions in preparation for when the warmer months arrive. Be sure to monitor and control the temperature to help the germination process for each of these vegetables.  
  • Plant/sow fast-growing vegetables such as pumpkins, cucumbers, courgettes, and sweet corn, again, for preparation to harvest in the early summer.  
  • You could also purchase ready-grown tomato and pepper plants to start introducing them to an unheated greenhouse environment.

Spring to Summer

  • As we head into the warmer time of year, people typically transfer the above-prepared vegetables into patches outside of their greenhouse. Before doing this, I recommend preparing their location and making sure the soil doesn’t lack any vital nutrients.

Summer to Fall

  • As summer ends, you’ll want to harvest your crops and entirely remove anything left over.
  • Now the summer crops have gone, you should start growing such things outside as calabrese, parsley, or French beans and bring them in as temperature falls.
  • For late harvests, you can have the most out of the fall sun by sowing lettuces and baby carrots, etc.
  • Around this time of year, people usually start planting potatoes in time for Christmas.

Fall to Winter

  • As we enter fall, you’ll want to bring your calabrese, parsley, and French bean seedlings indoors so they’re able to mature for next year.
  • During winter, you can start preparing for the coming months. Here you’ll want to repeat the planting process shown above.

The great thing about growing your own vegetables is that the process is simply just rinse and repeat. To begin with, it can seem like a lot. But if you dedicate certain areas of your greenhouse depending on your vegetable’s growth stages, it should be pretty manageable.


After reading the above, you should have a solid understanding of when, how, and why you should put your plants inside a greenhouse during the winter months. Knowing this information is vital for any avid gardener. We devote our precious time to get summer flowers to flourish spectacularly, and why would you want them to waste away from frost damage? If you’re able to maintain their ideal environment yearly, they’ll grow into something more fabulous the following year.

We’ve also spoken about how to utilize your greenhouse to grow vegetables all year round. A common misconception I hear from gardeners is that they don’t have enough time or knowledge to take full advantage of their greenhouses. To make this easier for many, I’ve broken the planning process into many small steps to ensure you implement it into your gardening routine.

Now, what is there left to do? Take notes and prepare your plants and greenhouse for the winter months coming our way to guarantee a healthier future for your treasured plants.