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Key takeaways
- Cool-season herbs like parsley, chives, cilantro, chervil and many thymes and oreganos handle a cold greenhouse far better than basil.
- Winter light is the main limit. Growth slows sharply once days get short, so start plants in early fall and harvest lightly.
- Water less and water in the morning. Soggy pots in cool air lead to root rot and mold.
- Tender perennials like rosemary, bay and lemon verbena overwinter well in a frost-free greenhouse, even if they don't grow much.
- Basil needs warmth and strong light. In winter it's a heated-greenhouse or grow-light crop.
The short answer
In a cold (unheated or barely heated) greenhouse, the herbs that keep producing are the cool-season ones: parsley, chives, cilantro, chervil, dill, and the hardy Mediterranean perennials like thyme, oregano and sage. In a frost-free greenhouse, you can add tender perennials like rosemary, bay and lemon verbena, mostly as plants you're protecting rather than harvesting heavily. Basil is the exception: it needs warmth and strong light, so in winter it belongs in a heated greenhouse or under grow lights.
If you're setting up herbs outdoors or on a windowsill, GardenGear's herb garden setup guide covers that side. This guide is about winter under cover.
Herb-by-herb: how each handles a winter greenhouse
| Herb | Cold greenhouse | Frost-free greenhouse | Notes |
|---|---|---|---|
| Parsley | Good | Very good | Steady harvests of outer leaves. Flat and curly both work |
| Chives | Good, may die back in deep cold | Good | Regrows fast from the clump |
| Cilantro | Very good | Good | Prefers cool weather and bolts in heat |
| Chervil | Very good | Good | Shade-tolerant, likes cool, damp conditions |
| Dill | Fair to good | Good | Sow in fall. Harvest young leaves |
| Thyme | Good | Good | Keep on the dry side. Hates wet roots |
| Oregano and marjoram | Fair to good | Good | Oregano is hardier than sweet marjoram |
| Sage | Good | Good | Slow in winter. Harvest sparingly |
| Mint | Dies back, regrows | Fair | Keep in its own pot |
| Rosemary | Risky in hard frost | Good | Watch watering closely |
| Bay laurel | Protect from hard frost | Good | Slow-growing. Light harvest only |
| Lemon verbena | Drops leaves | Survives dormant | Treat as overwintering, not harvesting |
| Basil | Poor | Poor to fair | Needs a heated house and good light |
"Cold greenhouse" here means unheated or heated only to keep off frost. "Frost-free" means heated enough to stay above freezing. Hardiness varies by variety and by how cold your greenhouse actually gets, so track it with a min-max thermometer.
Light: the real winter limit
In winter, light, not cold, is usually what stops herb growth. Once days drop below roughly ten hours, many plants slow to a crawl, a pattern often called the Persephone period. We explain it in the 10-hour light rule.
What that means in practice:
- Start early. Sow or pot up herbs in late summer and early fall so they're well established before short days arrive. Plants that go into winter big will keep producing slowly. Plants that go in small will mostly wait.
- Use your brightest spot. Put herbs on the sunniest bench, close to the glazing, and keep glazing clean.
- Harvest lightly. Take a few leaves or stems from each plant instead of cutting one back hard. Regrowth is slow in winter.
- Consider supplemental light. A grow light on a timer can keep basil and other light-hungry herbs going. See best greenhouse grow lights and greenhouse lighting science.
Watering in winter
Overwatering kills more winter herbs than cold does. Cool air, low light and slow growth mean pots dry out much more slowly than in summer.
- Check before you water. Push a finger into the mix. Water only when the top inch or so is dry, and less often for thyme, rosemary, sage and oregano.
- Water in the morning so foliage and the surface dry before the cold night. Evening watering adds to overnight condensation. See autumn condensation and gray mold.
- Water the soil, not the leaves.
- Use free-draining mix and pots with holes. Mediterranean herbs especially need sharp drainage.
- Let very cold water warm up. Many growers keep a can of water inside the greenhouse so it isn't ice-cold.
Spacing and airflow
Crowded herbs in still, damp winter air are an invitation to mildew and gray mold. Space pots so air moves between them, prune out yellowing leaves, and run a circulation fan if you have one. Best greenhouse fans covers small options.
Containers or beds?
Both work. Containers let you move herbs into the best light, group them by watering needs, and bring tender plants into warmer spots on cold nights. Border beds hold more warmth and moisture, which suits parsley, chives and cilantro. Many growers do both: hardy herbs in beds, tender and Mediterranean herbs in pots.
Worked example: a winter herb bench in a 6x8 greenhouse
Here's a practical setup for a small, frost-protected greenhouse:
- In early September: sow cilantro, chervil, dill and parsley in pots or a border bed. Pot up chives, thyme, oregano and sage from the garden, or buy young plants.
- In late September: bring in potted rosemary and bay before the first frost. Check for pests first. See bringing container plants under glass without importing pests.
- In October: sow a second round of cilantro and chervil for late-winter picking.
- November to February: harvest lightly, water sparingly in the morning, keep the fan running, and vent on mild days.
- In late February: as light returns, growth picks up. Pot on anything root-bound and start basil under lights or in a heated spot.
Pests and problems
- Aphids and whiteflies can build up on herbs in a warm winter greenhouse. Check leaf undersides and use sticky traps to monitor.
- Powdery mildew and gray mold follow damp, still air. Improve airflow and cut back watering.
- Leggy growth means too little light. Move plants closer to the glazing or add a grow light.
- Bolting cilantro means it got too warm. Keep it in the coolest part of the greenhouse.
Heated or unheated?
An unheated greenhouse can keep hardy herbs picking through much of winter in milder regions, and it protects them from wind, rain and snow even when growth stops. A heated greenhouse broadens the list and keeps tender perennials alive. Our heated vs unheated greenhouse guide compares the costs, and how to heat a greenhouse efficiently explains how to keep running costs down.
Frequently asked questions
What herbs grow in a greenhouse in winter?
In an unheated or barely heated greenhouse, parsley, chives, cilantro, chervil, dill, thyme, oregano and sage do well. In a frost-free greenhouse you can also keep rosemary, bay and lemon verbena. Basil needs warmth and strong light.
Can you grow basil in a greenhouse in winter?
Only in a heated greenhouse with good light, or under grow lights. Basil doesn't tolerate cold and grows poorly on short winter days.
How often should I water herbs in a winter greenhouse?
Much less than in summer. Check the mix with your finger and water only when the top layer is dry, in the morning, at the soil level. Mediterranean herbs like thyme and rosemary need even less.
Do herbs grow in winter in an unheated greenhouse?
Hardy herbs like parsley, chives and cilantro keep growing slowly in milder weather and survive colder spells under cover. Growth slows sharply in the shortest days, so start them early and harvest lightly.
Should I use grow lights for winter herbs?
Grow lights help if you want steady harvests, especially of basil and other light-hungry herbs. Hardy herbs can manage without them if they're well established before short days arrive.
Can I bring rosemary into the greenhouse for winter?
Yes, rosemary overwinters well in a frost-free greenhouse. Check it for pests before moving it in, keep it in a bright spot, and water sparingly.