Growing vegetables in a greenhouse during winter can extend the production of cool-weather crops. As long as you can keep your greenhouse from dropping below temperatures where the plants you're growing are hardy, you'll be able to enjoy fresh vegetables long after the same crops would stop producing if they were growing outdoors without protection from the elements.
It's important to have realistic expectations for wintertime greenhouse gardening. You won't to able to produce vegetables that require a lot of sun and heat (such as tomatoes, eggplants, peppers, etc.) in an ordinary greenhouse over the winter, but you absolutely can grow - and harvest - quite a few cool-season veggies this way.
Best Greenhouse Vegetables to Grow in Winter
When growing cool weather vegetables in a greenhouse, your goal should be to keep the temperature above (or as close to) freezing as possible. The frost-resistant vegetables listed below can tolerate temperatures at - or even slightly below - freezing.
Broccoli - Start your broccoli plants in fall, then keep them going all winter in your greenhouse so you can enjoy fresh broccoli during the coldest months of the year.
Broad beans - Also known as fava beans, broad beans - unlike other beans - are cool-weather crops. Start them prior to first frost and keep them growing over winter for an early spring harvest.
Cabbage - Cabbage is a great candidate to grow in winter greenhouses. It thrives in conditions as low as 27°F, and the cover of a greenhouse will continue to protect it from pests when spring arrives.
Carrots - Carrots do well in temperatures as low as 20°F, so you can actually alternate them between outdoors and your greenhouse depending on the weather forecast.
Cauliflower - Cauliflower grows well when it's cold (as low as 25°F), and it even tastes better after at least a light frost. Growing cauliflower in a greenhouse means you can enjoy it all winter.
Green peas - Cool weather peas - which all green peas are - will keep growing when temps stay above 40°F and will survive light frosts. So, they're great candidates for winter greenhouse growing.
Kale - Kale is extremely cold hardy, so you really only need to put it in a greenhouse if you frequently get temps below freezing. It'll do great even in cold and drafty greenhouses that dip down to well below freezing.
Kohlrabi - Kohlrabi is a cool-weather crop that will grow well in a greenhouse during winter. It has similar needs as cabbage, so it can handle temperatures in the upper 20s (°F).
Lettuce - A greenhouse makes it possible to grow and enjoy fresh lettuce all winter. Some varieties are more cold tolerant that others and can even survive temperatures in the teens (°F).
Onions - You won't be able to harvest onions in the winter, but it's a good idea to start onion seeds in your greenhouse (or indoors) in mid-to late winter to get a head start on spring planting.
Spinach - Spinach is one of the most cold-hardy crops. It doesn't like warm weather and thrives in cold conditions. You can keep it going all winter as long as the temperature in your greenhouse stays above 15°F.
Swiss chard -Swiss chard can also survive temperatures as low as 15°F, so it's a great plant to grow in a greenhouse over winter. It also does okay in heat, so you can move it outside in spring or summer.
If you live in an area where it rarely freezes, you may be able to grow these vegetables outdoors all winter, as well as in a greenhouse. If your area gets hard freezes, you'll be able to keep them going much longer - maybe even until spring - by growing them in a greenhouse or a cold frame.
