15 Things To Grow in Unheated Greenhouses (Explained)

There is usually a sense of pride and satisfaction from eating vegetables cultivated in your own greenhouse.

What’s more, harvesting and eating fresh produce all year round is a dream most people have, especially during winter.

So if you are a gardening enthusiast, you’ll be glad to know that an unheated greenhouse can go a long way in helping you actualize this dream:

Here’s Why you Should Plant in an Unheated Greenhouse:

An unheated greenhouse gives you a large variety of plants for you to plant, especially hardy ones. Your plants are protected from pests and adverse outdoor weather conditions. Growing the right plants in an unheated greenhouse makes sure that you won’t have any additional energy costs on heating.

15 Things To Grow in Unheated Greenhouses (Explained)

At What Temperatures Do People Use Unheated Greenhouses?

Also known as a cold greenhouse, an unheated greenhouse is usually constructed in a cold frame or hoop type of garden building that absorbs heat from the sun while protecting the plants inside at the same time.

But what temperatures do most enthusiasts use in unheated greenhouses?

An unheated greenhouse is heated only by the sun. When the outside temperature falls to 20˚F, the minimum temperature inside an unheated greenhouse is 28˚F.

This means that for most people, their unheated greenhouse is usually 8˚F warmer than outside.

There isn’t an exact temperature that most enthusiasts keep their unheated greenhouses at because temperature usually varies from place to place, and the temperature inside a greenhouse is affected by the temperature outside.

However, most unheated greenhouses are usually 8˚F warmer than outside.

15 Most Popular Things To Grow in Unheated Greenhouses:

Eating fresh produce all year round is every gardener’s dream.

Some people may think that growing crops, especially during the winter, is a hard and impossible task, but as you will see, there are numerous crops that you can grow and thrive well in greenhouse conditions.

Unheated greenhouses, otherwise known as cool greenhouses or winter greenhouses, are the easiest to handle and maintain.

In most areas, no heat is required since the structures absorb the sun, and the product is protected from adverse weather outside.

With these structures, there is a list of crops you can grow easily. They include:

1. Onions

Several onion varieties can be sown in an unheated greenhouse and grow throughout the winter.

These include Electric (red), Radar (yellow), and Shakespeare (white).

2. Shallots

There are usually a variety of shallots from most garden centers that you can plant in unheated greenhouses.

One of the most recommended varieties is Jermor.

3. Peas

Peas are a great crop to have in an unheated greenhouse.

They are surprisingly hardy and will flourish even during the winter when temperatures drop below zero.

If you sow them directly into the ground, plant them one inch deep and relatively close at about one inch apart.

Good varieties include Snow Peas and Meteor.

4. Beans

Broad beans are an exceptional crop to have in your unheated greenhouse.

Some of the varieties that most people prefer are Aquadulce Claudia (AGM) and Super Aquadulce.

5. Garlic

Growing garlic in an unheated greenhouse is easy.

Plant the cloves individually at a depth of 2.5 inches on light soil and about 1 inch on hard soils.

Good examples of garlic varieties you can plant in your unheated greenhouse include Provence Wight and Solent Wight.

6. Lettuce

There is a couple of winter hardy lettuce that you can grow in your unheated greenhouse.

One such variety is Arctic King, which most greenhouse enthusiasts agree does well in unheated greenhouses.

Other varieties that can thrive in an unheated greenhouse include Endive and Radicchio.

7. Carrots

Carrots are a popular plant to grow in unheated greenhouses.

Some varieties that can thrive in such an environment include Chantenay carrots, Rondo, and Early French Frame.

8. Brussel Sprouts

These are perfect for unheated greenhouses.

They take around three months to grow and should be harvested when they’re about 1-2 inches in diameter.

9. Cabbage

Cabbage can grow throughout the whole of winter.

This makes them an outstanding choice for unheated greenhouses.

10. Spinach

These leafy greens can brave the cold, making them a good choice for growing in an unheated greenhouse.

Some good varieties you can grow include Merlo Nero and Riccio dÁsti.

11. Kale

Kale can survive temperatures as low as 21.2˚F.

This makes it possible veggie that you can sow in your unheated greenhouse.

12. Potatoes

You can grow potatoes in your unheated greenhouse.

Just make sure to grow them in sacks or large buckets/flower pots because potatoes are susceptible to frost.

It is recommended to fill the container with two parts garden soil and one part compost for the best results.

13. Pak Choi

This is an oriental vegetable that can be a great addition to a stir fry or noodle dish.

This veggie can flourish in an unheated greenhouse. Leaves take 30 days to be ready for harvesting, and the full plant will take close to 70 days.

14. Broccoli

Just like cabbages, broccoli can withstand cold and grow throughout the whole of winter.

So they are an amazing choice to have in your unheated greenhouse.

15. Cauliflower

Cauliflower is surprisingly cold tolerant and can thrive well in an unheated greenhouse.

Here are a few tips for growing these plants in your unheated greenhouse:

Space is crucial to maximizing the growth of your plants inside the unheated greenhouse. If you prefer using containers, make sure that you space your plants far enough apart so that their leaves don’t touch.

Additionally, if you prefer raised garden beds, make sure to thin out the weak plants as they grow so that hardier plants have enough room to thrive.

If you notice any signs of disease in your crops, remove them right away to control the disease and stop it from spreading.

Plant some naturally repellent plants such as marigolds to keep pests under control.

10 Things to NOT Grow in Unheated Greenhouses:

Typically, you can grow almost anything in a greenhouse.

Most plants will grow well in such a controlled environment. But while this may be the case, some crops are definitely not suited for an unheated greenhouse.

Some of these crops that may not do well in an unheated greenhouse need wind pollination or direct, full sunlight, which is not the case in unheated greenhouses.

They include:

1. Wheat

This crop requires wind to be pollinated, and as such, it may not do well in an unheated greenhouse.

2. Corn

Besides requiring wind to be pollinated, corn takes up too much space; thus, it may not be the best plant to have in your unheated greenhouse.

3. Rice

This plant requires a lot of water to grow, which makes having it in a greenhouse problematic.

4. Watermelon

Watermelons take up too much space, and thus having them in your unheated greenhouse may not be the best idea.

5. Radish

This plant needs a lot of direct and full sunlight for it to flourish. So it may not be well suited for an unheated greenhouse.

6. Turnips

Root vegetables such as turnips require deep soil.

They are, therefore, not a good choice for your unheated greenhouse. Turnips benefit from sowing directly in the ground, so they’re better suited outdoors.

7. Oats

Oats are wind pollinated and are therefore better of growing outdoors than in your unheated greenhouse.

8. Rye

This plant takes up too much space and is therefore not ideal for an unheated greenhouse.

9. Tomatoes

Tomatoes are climbers, and therefore, they can shield other plants you may have in your unheated greenhouse from the sun.

So it would be best if you did not plant them in your greenhouse.

Alternatively, if you’d really like to have them, consider installing vertical sticks to support and guide their branches.

10. Rutabaga

This plant requires exposure to full and direct sunlight.

As such, it may not be a good idea to plant it in your unheated greenhouse.

All in all, an unheated greenhouse can provide you with fresh produce throughout the year.

Additionally, you won’t have to spend a dime heating your greenhouse whenever it gets too cold.