What to Grow in a Greenhouse in Winter: 15 Easy Crops and a Planting Plan
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In an unheated greenhouse, the best winter crops are cold-hardy greens and roots: spinach, kale, lettuce, mâche, arugula, Asian greens, Swiss chard, carrots, radishes and scallions. The key is to plant in late summer and early fall so plants are well established before short, dark days slow growth.
A greenhouse can keep your kitchen supplied with fresh food right through winter, even without heat. Glass or polycarbonate traps daytime warmth and shelters plants from wind, frost and heavy rain, so hardy crops keep growing when outdoor beds are frozen.
Success in winter has more to do with light and timing than temperature. This guide covers which crops to choose, when to sow them and simple ways to protect them through the coldest weeks.
By NovaAgri Team · Updated November 2026 · Based on extension horticulture guidance and four-season growing practice
Key takeaways
- Choose cold-hardy greens, herbs and roots for unheated greenhouses
- Sow most winter crops from late summer to early fall
- Growth slows sharply when days are shorter than about 10 hours, so plants must be established before then
- Use row cover inside the greenhouse for extra frost protection
- Ventilate on sunny days to prevent overheating and disease
15 easy crops for a winter greenhouse
- Spinach: one of the hardiest greens and often sweeter after frost
- Kale: pick leaves all winter from established plants
- Lettuce: choose cold-tolerant leaf and butterhead varieties
- Mâche (corn salad): tiny, tender and extremely cold-hardy
- Arugula: fast growing with a peppery bite
- Asian greens: bok choy, tatsoi and mizuna thrive in cool weather
- Swiss chard: colorful and productive into winter
- Claytonia (miner’s lettuce): a reliable winter salad green
- Carrots: sow in late summer for sweet winter harvests
- Radishes: quick crops for gaps between greens
- Scallions: hardy and easy to grow in rows
- Parsley: keeps producing in cool conditions
- Cilantro: prefers cool weather and bolts less in winter
- Microgreens: harvest in one to three weeks on a bench
- Garlic: plant cloves in fall for a summer harvest
Step-by-step: planning your winter greenhouse
01
Plan around light
Short days slow growth far more than cold does. In many regions, from late fall to midwinter days are shorter than about 10 hours and plants barely grow. Plan to have crops mostly grown by then, so winter becomes a time of harvesting rather than growing.
02
Sow at the right time
Start most winter crops from late summer to early fall, roughly six to ten weeks before your first frost. Sow a second round of fast greens such as arugula, radish and Asian greens a few weeks later for a steady supply.
03
Prepare beds or containers
Refresh beds with compost before planting. Ground beds and large containers hold more warmth than small pots. If you use benches, choose deep trays and group them together.
04
Add extra frost protection
On the coldest nights, drape floating row cover over crops inside the greenhouse. This double layer can make a meaningful difference on frosty nights. Barrels or jugs of water act as thermal mass, absorbing heat during the day and releasing it at night.
05
Water carefully
Plants use much less water in winter. Water in the morning so leaves dry before night, and only when the top inch of soil is dry. Overwatering in cold, damp conditions invites rot and fungal disease.
06
Ventilate on sunny days
Even in winter, a closed greenhouse can overheat on a bright day. Open vents or doors in the late morning and close them in mid-afternoon to trap warmth before evening. Good airflow also reduces mildew and gray mold.
- A min-max thermometer shows how cold it really gets at night
- Automatic vent openers make ventilation effortless
- Remove yellowing leaves to improve airflow
07
Harvest little and often
Pick outer leaves of greens like kale, chard and lettuce so the center keeps producing. Avoid harvesting frozen leaves; wait until they thaw in the morning sun to prevent damage.
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Pro tip: Want tomatoes, peppers or cucumbers in winter? They need a heated greenhouse with steady nighttime temperatures and, in most regions, supplemental grow lights. Cold-hardy greens are far cheaper and easier for an unheated house.
Frequently asked questions
Can you grow vegetables in an unheated greenhouse in winter?
Yes. Cold-hardy crops like spinach, kale, mâche, lettuce, Asian greens, carrots and scallions grow well in unheated greenhouses, especially with row cover for extra protection.
When should I plant my winter greenhouse?
Sow most winter crops from late summer to early fall, so plants are established before days get shorter than about 10 hours.
How cold can a greenhouse get at night?
An unheated greenhouse is usually only several degrees warmer than outside at night. Row cover, thermal mass and good sealing help hold more warmth.
Do I need grow lights in a winter greenhouse?
Not for hardy greens, which grow slowly but steadily with natural light. Grow lights help if you want faster growth, seedlings or warm-season crops.
What is the easiest winter greenhouse crop?
Spinach, mâche and Asian greens are among the easiest and most cold-tolerant. Microgreens are the fastest, ready in one to three weeks.
The bottom line
Focus on cold-hardy greens, herbs and roots, sow them in late summer and early fall, add row cover on the coldest nights and ventilate on sunny days. With that plan, even an unheated greenhouse can give you fresh harvests all winter.
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