11 Best Winter Greenhouse Plants That Survive Cold Weather

Greenhouse planting is an excellent way to grow winter vegetables and extend their growing season. By using a greenhouse, you can ensure your plants thrive throughout the cold months, even without heating overnight.

However, it’s crucial to choose the right crops, as not all are frost-tolerant. To help you make the best choices, we’ve compiled a list of winter greenhouse plants that can easily withstand cold weather, allowing you to enjoy a bountiful harvest even in winter.

Explore the options and start planning your winter garden today!

Plants Survive Winter in A Greenhouse

Do you still need to decide which winter greenhouse plants to choose which can survive cold temperatures? Don’t worry! You are here to help you identify the best ones to grow in your greenhouse garden. They can tolerate an unheated greenhouse.

Thus, they won’t bother you with a complicated heating system that costs you a lot of money. Curious? Let’s get on the list!

1. Beets (Beta Vulgaris)

Winter Greenhouse Plants — Beets (*Beta Vulgaris*)

Beets, with their bright magenta hue, are great for salads and natural dyes. They thrive in USDA zones 2 to 11, preferring cool temperatures between 60°F and 70°F. Ensure your greenhouse maintains these conditions with proper heating and sun exposure for optimal growth.

2. Carrot (Daucus Carota)

Carrots are a nutrient-packed, cool-season vegetable that thrives in sandy, loamy, well-drained soil. The best time to sow them is between April and July or 10-12 weeks before the first fall frost, ensuring optimal greenhouse conditions.

Keep the greenhouse temperature between 50°F – 85°F for successful growth, as they thrive in USDA hardiness zones 3 to 11.

3. Celery (Apium Graveolens)

Celery, often mistaken for an herb due to its strong aroma, is a favored greenhouse vegetable in winter because it is easy to care for. It thrives in temperatures as low as 36°F but struggles above 86°F, making it suitable for USDA zones 4 to 10.

When planting in a greenhouse, ensure at least 16 hours of light exposure with grow lights to support growth and prevent frost damage.

4. Dill (Anethum Graveolens)

To grow dill in a winter greenhouse, maintain a temperature between 60°F and 75°F, even though the herb can tolerate down to 25°F.

Dill needs full sun exposure and moist, well-drained soil, so place it in a south-facing spot in your greenhouse. Sow the seeds from May to July to take advantage of warmer conditions, adjusting greenhouse temperatures as needed during colder months.

5. Kale (Brassica Oleracea)

Kale is an excellent choice for winter greenhouse gardening due to its ability to thrive in temperatures as low as 14°F. This cool-season veggie requires bright light, so ensure your greenhouse has transparent walls for optimal sunlight exposure.

Plant kale in late winter to early spring for a summer harvest, or in late summer for a winter harvest.

6. Lettuce (Lactuca Sativa)

Lettuce is a versatile cold-season crop that thrives in greenhouses, especially when temperatures range from 70°F to 75°F. It can withstand winter temperatures as low as 20°F but needs protection like plastic wraps to maintain optimal warmth.

Ensure at least six hours of sunlight and use loamy soil mixed with compost for healthy growth.

7. Mint (Mentha)

Mint, with its intense aroma and cooling effect, is a great choice for winter greenhouse cultivation. It thrives in USDA hardiness zones 3 to 8, enduring temperatures as low as -20°F.

Ideal growing conditions range from 55°F to 70°F, making mint suitable for unheated greenhouses during frost-free spring or fall.

8. Parsley (Petroselinum Crispum)

Parsley, a globally popular culinary herb, thrives well in USDA hardiness zones 4 to 9 and can withstand freezing temperatures as low as 20°F. This makes it an ideal winter greenhouse plant, as it requires minimal heating and prefers cool, moist soil conditions.

Growing parsley in lined pots or raised beds in a greenhouse with some frost protection, like plastic wraps, ensures a steady supply of fresh, aromatic leaves all winter long.

9. Peas (Pisum Sativum)

Peas, commonly mistaken for beans, are cold-tolerant vegetables that thrive in USDA hardiness zones 3 to 11. They can withstand light frost around 40°F but aren’t frost-hardy, so it’s crucial to maintain temperatures above freezing to avoid root rot.

Using natural heat absorbers like water bottles or dark bark wood in your greenhouse can help keep peas growing during winter without relying on expensive heaters.

10. Radish (Raphanus Sativus)

Radishes, a spicy root vegetable from the Brassicaceae family, thrive in cooler temperatures between 41°F and 86°F. They can handle cold weather as low as 27°F, making them ideal for winter greenhouse planting.

To protect radishes in harsh winters, use thermal mass materials and heat insulation, like plastic wraps, to maintain a stable environment.

11. Swiss Chard (Beta Vulgaris Subsp. Vulgaris)

With its vibrant red veins and spinach-like flavor, swiss chard is a popular choice for winter greenhouse gardening due to its ability to tolerate temperatures as low as 15°F. It’s best grown as an annual in USDA zones 3 to 10, ideally 2 to 4 weeks before the last frost in spring.

To protect your plants from freezing in the greenhouse, consider using thermal curtains or thermal mass materials to insulate heat effectively.

Final Thought

Besides flowering plants, greenhouses are ideal for growing crops you can harvest during the season. Some of the most recommended winter greenhouse plants, because they can grow in almost all areas of the USDA hardiness zones, are beets, radishes, Swiss chard, and peas. They are also resistant to quite extreme cold temperatures.

Thus, it makes it easier for you to care for it during the winter. You can also cut the budget for heating installation in your greenhouse since most vegetables and herbs can survive unheated.

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FAQs (Frequently Asked Questions)

How much warmer is an unheated greenhouse?

An unheated greenhouse can be up to 30°F warmer than the outside, depending on heat insulation like plastic wraps and thermal mass. This temperature difference helps maintain a stable environment for plants even without heaters.

How to keep plants in a greenhouse in winter?

To keep plants warm in a greenhouse during winter without electricity, use thermal mass by filling plastic bottles with water, painting them, and placing them in the greenhouse to absorb and release heat. Additionally, wrap potted plants with bubble wrap and consider using grow lights for added warmth and light.

Will an unheated greenhouse keep plants from freezing?

Yes, an unheated greenhouse can protect plants from freezing by maintaining a temperature about 5°C warmer than outside, thanks to insulation from fleece, bubble wrap, and thermal mass materials like water and soil. These elements help trap and release heat, keeping the greenhouse environment warmer.

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

In an unheated greenhouse during winter, you can grow cool-season crops like spinach, kale, Swiss chard, carrots, beets, and radishes. Herbs such as parsley, chives, and mint also thrive well; consider using bubble wrap to protect the roots in colder temperatures.

What flowers can you grow in the greenhouse over winter?

In a greenhouse over winter, you can grow irises and calla lilies in December, hyacinths, tulips, and daffodils in January, and orchids in February. Each flower thrives best in specific winter months due to varying temperatures.

What is the lowest temperature plants can survive in a greenhouse?

Plants in a greenhouse can generally survive in temperatures as low as 45°F at night during winter. To protect your plants from damage, it’s essential to have a proper heating system in place, especially during these colder temperatures.