What to Grow in a Greenhouse This Fall and Winter

A greenhouse can extend your gardening season long after summer crops begin to fade. It provides a protected place for your vegetables as the nights get colder, like seedlings, herbs, or tender plants that would struggle outdoors as temperatures drop.

The key is to choose crops that suit the conditions of your garden. For instance, an unheated greenhouse in a cold region will not grow tomatoes through winter. But it can be great for protecting hardy greens, extending the harvest, and giving you an earlier start when spring arrives.

What to Grow in a Greenhouse in Fall and Winter?

For most gardeners, the best greenhouse crops for fall and winter are ones that handle cool temperatures and shorter days. Good options include lettuce, kale, spinach, radishes, carrots, herbs, bok choy, and other Asian greens.

They are generally much easier to manage in cold climates than their warm-season counterparts. Leafy greens are ideal because you can harvest them a bit at a time instead of waiting for a large batch to mature.

Keep in mind that winter growth is slower. A plant may stay healthy without producing as quickly as it did in the summer, especially once daylight hours get shorter.

Best Crops for a Fall Greenhouse

Fall is one of the easiest times to grow in a greenhouse. Outdoor temperatures are dropping, but you still have a reasonable amount of light exposure.

Lettuce

Lettuce does well in the cooler conditions of fall, particularly varieties that handle cool weather. Loose-leaf lettuce is a good choice to grow in a greenhouse, because you can pick the outer leaves and let the plant keep growing.

Kale

Kale is a good choice when you want something that can stay productive as temperatures drop. Pick the outside leaves as needed and leave the growing point intact. Just a few plants can provide greens for quite a while.

Radishes

Radishes come in handy when the growing window is short. They mature quickly and don't take up much space, so it’s easy to grow them between larger crops.

Carrots and Beets

Carrots and beets can be planted in fall and left to mature gradually. In colder regions, having a greenhouse can give them more protection than an exposed garden bed. 

Spinach

Spinach is one of the easiest crops to grow in fall. It likes cool weather and is much less likely to bolt once summer heat is gone. Plant a little at a time rather than filling your greenhouse in one go.

Asian Greens

Bok choy, mustard greens, and similar crops are well suited to cool weather. They're worth trying if you want something that grows quickly and gives you more variety for your garden greens.  

Crops to Grow in a Greenhouse in Winter

In milder climates, an unheated greenhouse may be enough to keep greens and herbs going for the majority of the winter. In colder regions, the same greenhouse may mainly serve as protection from rain, snow, and temperature swings.

Spinach, kale, parsley, Asian greens, and root vegetables are good options to start with. Don't expect winter crops to grow at the same speed as they did in winter. With shorter days and cooler temperatures, many plants slow down quite a bit.

What to Grow Based on Harvest

For quick harvests: Try radishes, baby greens, arugula, lettuce, and some Asian greens.

For crops you can harvest for longer: Go with kale, spinach, chard, or parsley. 

For vegetables that can stay in the greenhouse: Carrots, beets, kale, and other cold-tolerant crops are good choices.

For summer plants going into fall: Herbs, peppers, and tomatoes can be kept in a greenhouse for longer, especially in mild climates. They will eventually need warmer conditions and more light. 

When Should You Move Plants Into a Greenhouse?

Start paying closer attention to nighttime temperatures when your area's first frost is approaching. Tender plants should be moved in before a cold snap, while cool-season crops can usually be moved or planted earlier.

Before bringing outdoor plants into a greenhouse, check them regular for pests and disease. A few minutes of inspection can save you from lots of time trying to get rid of an infestation later.

Prepare Your Greenhouse for Fall

Before planting, clean out old leaves and plant debris and check that your doors, panels, and fasteners are in good condition. Also check drainage and make sure you still have enough room to water, harvest, and tend to your plants.

Vego's Pacific Greenhouse is specifically designed for year-round gardening, with polycarbonate panels for insulation and vents to improve airflow. For best results, position the greenhouse on a stable surface with proper drainage and support.

How to Control Greenhouse Temperature in Winter

An unheated greenhouse can extend the growing season, but it won't maintain summer temperatures in the heart of winter. In colder regions, you may need insulation, additional covers, or supplemental heat for certain crops. 

It's better to choose crops that fit your greenhouse than to spend winter trying to keep warm-season plants alive.

How to Manage Humidity

Check the soil before watering rather than following your summer routine. Leave enough space between plants for air to move, and ventilate when weather conditions allow. Overwatering is especially common in winter because plants are growing more slowly and don't use water as quickly.

If you see persistent condensation, damp foliage, or stagnant air, take it as a sign that the greenhouse needs more airflow.

Make Better Use of Your Space

Raised garden beds make it easier to organize crops, while containers are useful for herbs, seedlings, and plants with specific watering needs. Trellises can also help you maximize vertical space without letting your plants take over walkways. 

Vego's Pacific Greenhouse is designed to accommodate raised garden beds, combining protected growing with an organized garden bed system. Remember to leave enough room to be able to reach your plants and maintain good airflow.

Do You Need Grow Lights in Winter?

Apart from lower temperatures, daylight also gets shorter in winter, and that can slow growth even when temperatures are ideal. In some climates, hardy greens and herbs can grow with natural light. In darker areas, grow lights can help, particularly for seedlings and greenhouses.

You don't necessarily need grow lights for every plant. Start by looking at how much direct sunlight your greenhouse gets and how quickly your plants are growing.

What Should You Avoid Growing in an Unheated Greenhouse?

Warm-season crops such as tomatoes, peppers, cucumbers, and eggplants need considerably more warmth and light than winter vegetables. You can often use a greenhouse to keep these plants going later into fall, but once temperatures drop further and daylight becomes limited, growth slows and fruit production can stop. 

A Simple Fall-to-Winter Greenhouse Plan

Think of the coming season in these three stages.

Early fall: keep harvesting summer crops while planting spinach, lettuce, radishes, herbs, and other cool-season vegetables.

Late fall: remove fading warm-season plants, fill open space with cool-season crops, and get your frost protection ready.

Winter: focus on cold-tolerant plants, monitor temperature and humidity, ventilate on sunny days, and reduce watering as plant growth slows.

The exact timing will depend on your region’s climate. Gradually replace warm-season crops with plants that are better suited to shorter days and colder nights.

FAQs 

What is the best vegetable to grow in a greenhouse in winter?

There isn't one best vegetable for every climate, but spinach, kale, lettuce, Asian greens, and some herbs are among the most reliable choices for cool-season greenhouse growing.

What should I plant in my greenhouse in September?

September is a good time to plant spinach, lettuce, kale, radishes, carrots, beets, Asian greens, and herbs, depending on your local climate and expected first frost.

Can you grow vegetables in an unheated greenhouse in winter?

Yes. Cold-tolerant vegetables such as spinach, kale, lettuce, and Asian greens can grow or remain productive in an unheated greenhouse, especially in milder climates. In colder areas, growth may slow considerably or stop during the coldest periods.

How cold is too cold for a greenhouse?

There is no single temperature that is too cold for every greenhouse or crop. An unheated greenhouse can protect plants from some outdoor exposure, but the inside temperature can still fall below freezing. Your crop's cold tolerance matters as much as the greenhouse itself.

How do I keep my greenhouse warm in winter?

Start with a well-insulated greenhouse, close vents and doors during cold nights, reduce drafts, and use additional protection or supplemental heat when necessary. Cold-tolerant crops are much easier to manage than trying to keep warm-season vegetables alive in an unheated structure.

Should I ventilate my greenhouse in winter?

Yes. Ventilation helps reduce excess heat and humidity, especially on sunny days. Even during winter, a greenhouse can become warm enough to need airflow.

Do I need grow lights in my greenhouse during winter?

Not necessarily. Hardy greens may grow with natural light in some climates, but winter daylight can be too limited for strong growth. Grow lights can help with seedlings and crops that need more consistent light.

How often should I water greenhouse plants in winter?

Check the soil rather than following a fixed schedule. Plants usually use less water in winter because growth is slower and temperatures are lower, so watering as often as you did in summer can lead to overly wet soil.

Can tomatoes grow in a greenhouse during winter?

They can in a heated greenhouse with suitable light and temperature, but tomatoes are not a good choice for most unheated winter greenhouses in cold climates. A greenhouse is more useful for extending the tomato season into fall than for keeping tomatoes productive through a cold winter.

Can a greenhouse extend the growing season?

Yes. A greenhouse can protect crops from cold, wind, and weather extremes, giving you more time to grow in both fall and spring. How much extra growing time you get depends on your climate, greenhouse design, crop choice, and whether you use heating or supplemental lighting.

Final Thoughts

A greenhouse gives you more options when the garden outside starts to slow down. Fall is a great time to switch from tomatoes and peppers to greens, herbs, and other cool-season crops, while winter is mostly about choosing plants that can handle lower temperatures and shorter days.

A handful of reliable crops will tell you a lot about how your greenhouse performs. Once you know what works, you can build your fall and winter planting around it - and keep harvesting after the outdoor garden slows down.