You can grow greens in winter by planting cold-hardy crops in late summer and early fall, then protecting them in a greenhouse. Spinach, kale, lettuce and Asian greens handle cold nights well. The secret is timing: get your plants mostly grown before the short days of late fall, and they will feed you all winter.
We are a small, woman-owned greenhouse business in Georgia, and winter greens are one of our favorite topics. This guide covers what to plant, when to plant it, how warm to keep it and how to harvest without killing your plants.
✅ Quick answer
- Best winter greens: spinach, kale, mâche, claytonia, arugula and winter lettuce types.
- Sow 6 to 12 weeks before your days drop under 10 hours. In much of the US, that means August to early October.
- Most hardy greens get by in an unheated greenhouse. Keeping it just above freezing gives you much more to pick.
- Water in the morning, and only when the soil is dry an inch down.
- Pick outer leaves and leave the center bud. The plant will keep producing.
Can you grow greens in winter in a greenhouse?
Yes. Leafy greens are the easiest winter crop there is. Many of them don't mind cold at all. What slows them down is the lack of light, not the chill.
A greenhouse helps in three ways. It keeps off wind, ice and snow. It traps the sun's warmth during the day. And it keeps rabbits and deer away from your salad.
Growers in snowy states pick greens all winter from unheated tunnels. So in a solid backyard greenhouse, a steady winter harvest is very realistic.
What greens grow best in a winter greenhouse?
Some greens shrug off hard frost. Others are better for fall and early winter, before the deepest cold. Here is how they compare.
| Green | Cold hardiness | Best use | Notes |
|---|---|---|---|
| Spinach | Very high | All winter | Often the top performer for winter growers |
| Kale | Very high | All winter | Red Russian is a favorite; flavor sweetens after frost |
| Mâche (corn salad) | Very high | All winter | Small rosettes, mild nutty flavor |
| Claytonia (miner's lettuce) | Very high | All winter | Tender leaves, great in salads |
| Arugula | High | Fall to spring | Fast; can overwinter |
| Winter lettuce | Medium-high | Fall and early winter | Try 'Winter Density' or 'Arctic King' |
| Swiss chard | Medium | Fall and early winter | May die back in deep cold, then regrow |
| Tatsoi, mizuna, bok choy | Medium | Fall and early winter | Handle frosty nights, but can turn mushy in hard freezes |
Notice a pattern? The hardiest greens are low, leafy and fast. They also tend to taste sweeter after a frost, which is a nice bonus.
When should I plant winter greens?
This is where most people go wrong. They plant in November and wonder why nothing grows. The problem is day length.
Know your "Persephone period"
Growers use this name for the weeks when you get less than 10 hours of daylight. During that time, most plants stop actively growing. They will hold in the cold, and you can still pick them, but they barely put on new leaves.
- Around Chicago, it runs roughly from early November to early February.
- In the Northeast, it is roughly mid-November to mid-February.
- The farther south you live, the shorter it is. In much of Georgia, it lasts only a few weeks around the winter solstice.
To find your dates, look up a daylight table for your town. The U.S. Naval Observatory publishes a free one online.
Work back from that date
📐 Winter greens planting date
Sow date = First day under 10 hours − Days to harvest
Days to harvest is on the seed packet · Most greens take about 30 to 60 days
🧮 Worked example: spinach near Chicago
- First day under 10 hours of light: about November 9
- Spinach days to harvest (typical packet): about 45 days
- Add about 2 weeks because growth slows as days shorten
November 9 − 45 days − 14 days = about September 10. Sow spinach then, and you will have full-size plants to pick from all winter.
Plants that are full size by then give you something to pick all winter. Smaller plants usually survive too. They sit still in the dark weeks, then take off when days pass 10 hours.
💡 Sow in waves: sow a short row every two weeks from mid-August to late September. You will get a steady supply instead of one big harvest, and you won't have to guess the perfect date.
How cold can a greenhouse get for growing greens?
Most hardy greens survive frost. Spinach, kale and mâche can handle nights well below freezing once they are established. But surviving is not the same as growing.
For a good harvest, aim for these temperatures:
- Unheated: fine for spinach, kale, mâche and claytonia in most of the US. Harvest slows in the coldest weeks.
- Kept just above freezing (35 to 40°F): the sweet spot for winter greens. Plants stay healthy and keep growing on sunny days.
- Kept at 40 to 45°F: good for lettuce, chard and Asian greens, and for starting spring seedlings.
You don't need to keep your greenhouse warm like a living room. Greens need far less heat than tomatoes or peppers.
How much heat do winter greens need?
Our greenhouse heating guide uses this formula. Here it is for a greens-only greenhouse.
📐 Greenhouse heat formula
BTU per hour = Surface area × U-value × Temperature gap
Surface area = walls + roof · U-value about 0.7 for twin-wall polycarbonate · Gap = inside °F minus coldest outside °F
🧮 Worked example: a Riga 4 kept at 35°F
- Surface area (walls + roof): about 390 sq ft (our estimate)
- U-value for 8mm twin-wall polycarbonate: 0.7
- Keep it 35°F inside on a 10°F night: gap of 25°F
390 × 0.7 × 25 = about 6,800 BTU per hour. Divide by 3.412 = about 2,000 watts, plus 20% = about 2,400 watts. Keeping tomatoes at 60°F on the same night needs about twice that.
That is why winter greens are such a good fit for a well-glazed greenhouse like the Hoklartherm Riga 4. You can see heaters of different sizes in our greenhouse heater collection. Prefer to skip electricity? Try these ideas for heating a greenhouse without electricity.
⚠️ Use a backup: if you rely on a heater, add a thermometer with an alarm or a small backup heater. One failed heater on the coldest night can undo a whole season of work.
How do I grow greens in a greenhouse step by step?
- Pick the sunniest spot. In winter, every hour of light counts. Put greens on the south side, away from shade.
- Prepare beds or containers. Use loose, well-drained soil with plenty of compost. Raised beds and large containers warm up faster than the ground.
- Sow or transplant. Direct-sow spinach, arugula and mâche. Start kale, chard and lettuce in trays, then transplant. Follow the spacing on the packet.
- Add a row cover inside. A layer of light row cover over hoops gives extra frost protection. Keep it off the leaves, and open it on sunny days.
- Water carefully. Check soil with your finger. Water in the morning so leaves dry before night.
- Vent on sunny days. Even in January, a closed greenhouse can heat up fast. Fresh air also lowers humidity.
- Harvest a little at a time. Start picking once plants have several full-size leaves.
💡 Use the vertical space: greens are short, so shelves and benches let you grow more in the same greenhouse. Browse our greenhouse shelves to stack trays of baby greens.
How often should I water greens in winter?
Much less than in summer. Cool air and short days mean the soil dries slowly. Overwatering is the most common winter mistake we hear about.
- Water only when the top inch of soil is dry.
- Water in the morning, never in the evening.
- Aim at the soil, not the leaves.
- Use water that isn't ice-cold. A barrel inside the greenhouse warms up and stores heat too.
For more on this, read our guide to how much water plants need in a greenhouse.
What pests and diseases attack winter greens?
Winter is quieter than summer, but problems still show up. Damp, still air is the main trigger.
- Downy mildew and other fungal problems: yellow patches and fuzzy growth under leaves. Improve airflow, water less and space plants out.
- Aphids: small soft insects on new growth. Check leaf undersides weekly and wash them off with water.
- Slugs: chewed holes, especially in lettuce. Remove hiding spots like boards and old leaves.
- Weeds like chickweed: they love cool weather. Pull them early before they spread.
A small fan that runs a few times a day keeps air moving. Our greenhouse fans range from small circulation fans to exhaust systems.
How do I harvest greens so they keep growing?
Think of each leaf as a small solar panel. The more leaves you leave, the more the plant can feed itself. So pick the outer leaves and leave the center.
- Harvest outer leaves of kale, chard, spinach and loose-leaf lettuce.
- Never cut out the growing point in the center of the plant.
- Cut baby greens about an inch above the soil. Many will regrow.
- In the darkest weeks, pick lightly. Plants regrow slowly until days pass 10 hours.
Pick in the late morning, after any frost on the leaves has thawed. Frozen leaves bruise easily.
Do I need grow lights for winter greens?
Not always. In the South and much of the middle of the country, winter sun is enough for hardy greens. Growth just slows down.
Grow lights help most in the North, or if you want fast growth in December and January. Run them to give plants 12 to 14 hours of light a day. See our greenhouse grow lights for options.
💡 Our customers' favorite trick: combine a sunny spot, a light row cover and a heater set just above freezing. That simple setup gives a steady winter harvest without big bills.
What greenhouse is best for growing greens in winter?
Any greenhouse helps. But glazing matters most in winter. Twin-wall polycarbonate holds heat better than single glass, so it costs less to keep frost-free. That's why our winter growers often choose a Riga greenhouse.
If you're shopping, we ship free to the continental US and can connect you with an assembly crew. We also offer a Price Match Guarantee - please check the rules.
Want to grow in pots instead of beds? Read our container gardening tips for greenhouses.
Frequently asked questions
Can I grow lettuce in a greenhouse in winter?
Yes. Choose winter types like 'Winter Density' or 'Arctic King', and sow in early fall. Lettuce does best if you keep the greenhouse just above freezing. It is less hardy than spinach or kale.
What is the easiest green to grow in winter?
Spinach is the easiest for most growers. It is very cold hardy, grows well in short days and keeps producing if you pick the outer leaves. Kale and mâche are close behind.
Do I need to heat my greenhouse to grow winter greens?
Not always. Hardy greens like spinach, kale and mâche often grow in an unheated greenhouse. A heater set just above freezing gives a bigger, steadier harvest, especially in the North.
When should I plant greens for a winter harvest?
Plant 6 to 12 weeks before your days drop under 10 hours. In much of the US, that is August to early October. Farther south, you can plant a little later.
Why are my winter greens not growing?
Most likely it is low light. When days are shorter than 10 hours, most greens almost stop growing. They will speed up again in late winter. Planting earlier next year is the fix.
How do I stop mold on greens in a winter greenhouse?
Water less, water in the morning, and vent on sunny days. A small fan keeps air moving. Space plants so leaves dry quickly.
Ready to grow greens all winter?
We are a small, woman-owned business in Georgia, and we answer every question personally. Tell us where you live and what you want to grow. We will help you pick the right greenhouse, heater and setup for a winter harvest.
