Skip to main content

Grow cold-hardy veggies in an unheated greenhouse this winter – here’s how

Think unheated greenhouses are only good for warm summer days? Think again!

Most of us love the crisp air and colorful leaves that come with fall and winter, but for those of us who enjoy gardening, those cooler temperatures bring new concerns about what to do with your plants. That is, unless you have a greenhouse.

Difficulty

Moderate

What You Need

  • Greenhouse (such as a cold frame or hoop structure)

  • Thermostat

  • Water system

  • Grow lights

  • Horticultural fleece

  • Horticultural or regular bubble wrap

If you have the space, greenhouses are one of the greatest resources any home gardener can have at their disposal. They expand how much you can grow during the season, they let you grow plants for a little longer than you would otherwise, and they allow you to have crops that are a bit more sensitive to weather and temperature fluctuations because you can house them in a controlled environment.

Best of all, you don't need to shell out for a fancy and expensive heated greenhouse solution. Here's how to make some small changes to get the most bang for your buck out of your unheated greenhouse this winter.

Small rounded greenhouse
Grundsteins / Shutterstock

Why would anyone want to use an unheated greenhouse?

An unheated greenhouse has its benefits, not the least of which is saving on heating costs. Because they’re outdoors, the sun will naturally heat the space during the day, even in the winter. So although there are concerns about inconsistency, you’ll still be able to save money and lower your bills during the colder parts of the year.

While you can’t grow warm-weather crops in an unheated greenhouse, that doesn’t mean you’re out of options. From root veggies to cold-hardy greens to starting seeds, there are plenty of things you can grow. Aside from that, the pros are the same as with any other greenhouse. You get to grow for longer than the regular outdoor season, protect dormant plants, and bring your container plants into an indoor environment without cluttering up your home.

Greenhouse in the backyard
Image used with permission by copyright holder

How to set up an unheated greenhouse at home

Setting up an unheated greenhouse is as simple as setting up a standard greenhouse, just without the heating system. You’ll want all the basics: a thermostat, a water system (if your greenhouse is large enough), and a few grow lights. If you’re the average home gardener, it’s likely that your greenhouse set-up isn’t that extravagant — likely a cold frame or hoop structure — so it shouldn’t be too difficult to get ready for cold weather growing.

Step 1: Set your greenhouse up in an area with lots of natural lighting and where it won’t get too rattled by the wind.

If lighting is poor, put in artificial grow lights to help your plants thrive.

Step 2: If possible, set up the greenhouse close to a water source, such as a hose, to make things simpler.

This will allow you to set up a water system more easily.

Step 3: The thermometer will be one of the most important parts of your unheated greenhouse, as it will help you keep an eye on how cold or how warm it is.

Although you can’t heat the space yourself, you can provide your crops with a little extra protection at night where needed and provide proper ventilation as temperatures start to warm up.

Greenhouse in winter
flora Asadi / Shutterstock

How to protect your crops without heat

An unheated greenhouse doesn’t mean your plants will go without protection — it just takes a little more work on your end. (Note: Unheated greenhouses may not be the best option for home gardeners who don’t have a lot of time to dedicate to manually caring for the space.)

Although greenhouses trap heat during the day and keep the cold-hardy crops relatively comfortable, nighttime winter temperatures can get a bit dicey. Frost can still damage crops in an unheated greenhouse, so you’ll have to give them extra protection and keep an eye on the forecast for when temperatures may drop.

Step 1: Protection for unheated greenhouses and their crops can be as simple as putting a layer or two of horticultural fleece over the plants and wrapping containers with bubble wrap.

You can also layer the inside of your greenhouse with horticultural bubble wrap, since the sunlight can still come through but it will help insulate and keep the cold out at night.

Step 2: Be mindful to remove the fleece or bubble wrap during the day to avoid overheating the plants.

Cold frame greens
Image used with permission by copyright holder

What can you grow in an unheated greenhouse in the winter?

When you have a greenhouse, the onset of winter doesn’t have to mean the end of fresh veggies and greens — and that’s true with unheated greenhouses, too! There are plenty of crops that are cold-hardy and able to withstand frosts and freezing temperatures. Plus, due to the nature of how greenhouses are built, sunlight will be able to naturally heat it more than you might think.

Starting seeds in unheated greenhouses is pretty easy too, and it can help you get your seasonal annuals ready in time for spring planting. Veggies like broccoli, carrots, and turnips are relatively cold-hardy and will grow well in an unheated greenhouse. You can also grow greens like spinach and kale, which means that you don’t have to forgo fresh side salads just because it’s winter! Their care requirements are relatively similar to the ones you follow during the growing season, so long as you’re mindful of overwatering and adding extra protection at night.

Getting good growth in your unheated greenhouse

Although it may be tempting to keep your plants closer together in an unheated greenhouse as an attempt to increase humidity and warmth, you want to do just the opposite.

Step 1: Make sure your plants have room to grow correctly.

Plants in an unheated greenhouse — similar to plants in an outdoor garden bed or controlled greenhouse — don't like being too tightly clustered together. They won’t grow as full as you’d like if they don't have room to stretch their legs, so to speak.

Step 2: Use plant containers to manage and allocate the space better and avoid overcrowding.

Step 3: If you choose to use raised garden beds, make sure you go through the same process of thinning out the weaker plants so that the stronger ones have space to thrive.

Now that you've got your unheated greenhouse set up, make sure you check in on it every day. In addition to adding protection at night (if needed) and removing it in the morning, you’ll want to inspect your plants for any signs of disease or pests. Damaged foliage should be removed as soon as possible to keep issues from spreading and allow the plant to direct energy to healthier parts. With care and a bit of luck, your winter harvest will be a bountiful one.

Editors' Recommendations

Kiera Baron
Former Digital Trends Contributor
Kiera Baron is a freelance writer and editor, as well as a budding digital artist, based in Upstate NY. She is currently one…
A complete guide to cleaning your greenhouse for beginners
greenhouse

When you first installed your greenhouse, it probably looked like a glittery glass castle for your lovely plants to grow and live in. However, weather, soil spills, and birds have made their mark on your greenhouse over time and now it's probably looking cloudy and nasty. So how do you clean a greenhouse?
Why worry about a clean greenhouse?
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.
What is the best way to clean a greenhouse?
You can use whatever cleaning method works for you, but here is our step-by-step process that we recommend.
Step one: Empty the space
Of course, we know you can only empty a greenhouse so much if you have tender plants that need to stay warm. But as much as you can, take out the tools, buckets, and bags of soil. It will be much easier on you if you don't have to fuss with items in your way as you clean the walls and floors. This also allows you to go through what you have and declutter if necessary.
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.

Read more
When and how to transplant tomato plants for the best results
baby tomato plants

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?

How do you transplant a grown tomato plant?
If you've never transplanted tomatoes before, the idea can be intimidating. You have all these tiny plants that you've cared for over the last several weeks, and now it's time to pluck them out of their nursery pots and plop them into the outside soil where they're exposed to sun, weather, and critters. Luckily, you've cared for them so well that they're healthy and robust plants that will be able to handle anything nature throws at them.
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.
Step two: Don't water the plants
Before you start pulling little plants out of their pots, you mustn't water the plants a few days before transplanting. Wet soil can make the transplanting process much harder on you and the plant. Dry soil falls away easier and is less likely to break off roots as you move the plants to their new home.
Step three: Prepare the new soil
The new location for your tomato plants will need to be prepped before you get all those babies out of their homes. Whether you are planting into the ground, a raised bed, or a pot, you'll want to amend the soil to guarantee that the plant has many nutrients to soak up. It also is easier if you dampen the soil right before transplanting. Damp soil is much more manageable and more easily manipulated around the plant.
Step four: Plant deeply
As you gently pull out the baby tomato plants, you'll want to shake off the old soil to expose the roots. This will ensure the plant has access to the new soil and nutrients you're about to provide it with. 

Read more
A complete guide to the best lights to choose for your greenhouse
Houseplants under grow lights

Just like growing houseplants indoors, growing plants in a greenhouse requires specific care and a suitable environment. Even though the greenhouse will have some light from the sun coming in, the glass panes are often filtered in some kind of way to prevent your plant’s leaves from scorching. Enter grow lights. They’re used most commonly in darker spaces or during colder months; however, they're greatly beneficial to your greenhouse plants and help ensure that the plants are getting the light they need to thrive.

Can you have an indoor greenhouse?
Absolutely! Indoor greenhouses are revered for how sustainable and inexpensive they can be. An indoor greenhouse with lights can be installed anywhere in the home where you have the space, and it’s a perfect place to grow things like fruits, herbs, and veggies indoors. If you’re only planning to grow a couple herbs, you can get something as small as a tabletop greenhouse! It will fit a few plants, won’t take up too much space, and will add to the aesthetic of a room while letting you grow plants in a unique way.

Read more