What to Grow in a Greenhouse in January (By USDA Zones)

Growing food in a greenhouse during January looks very different depending on where you live. In colder regions, it’s about protecting hardy crops and maintaining what you planted in fall, while warmer zones can support active growth and even fruiting plants. This guide breaks down what to grow in a January greenhouse by USDA zone, with practical examples, realistic expectations, and tips based on real winter growing conditions.

Understanding January Greenhouse Growing

January greenhouse growing is less about fast growth and more about protecting plants from extreme cold while managing limited sunlight. Even in a greenhouse, winter light levels are low, meaning plants grow slower than they do in spring or summer.

USDA hardiness zones describe the average minimum winter temperatures in a region. They do not account for day length, cloud cover, or greenhouse insulation, all of which play a major role in January success.

In January, greenhouses are best used for cold-hardy crops, steady harvests of greens, and starting slow-growing plants for spring. Heated greenhouses expand options, but even unheated structures can be productive with the right crops.

What to Grow in January: USDA Zones 3–5

Zones 3–5 include much of the Upper Midwest, Northern Plains, New England, and higher elevations. Outdoor temperatures regularly drop below freezing, and daylight hours are short.

Best Crops for Cold Northern Zones

• Spinach: Extremely cold-hardy and capable of surviving near-freezing conditions when protected.
• Mâche (Corn Salad): A mild-flavored winter green that thrives in low light.
• Claytonia (Miner’s Lettuce): Grows slowly but reliably in cold greenhouses.
• Green onions: Regrow easily from sets or leftover roots.

In these zones, most January greenhouse production focuses on harvesting crops planted in fall rather than new sowings. Supplemental heat, even a small amount, can significantly improve plant health and growth consistency.

What to Grow in January: USDA Zones 6–7

Zones 6–7 cover a large portion of the central and mid-Atlantic United States. Winters are cold, but prolonged deep freezes are less common.

Reliable January Crops

• Lettuce: Loose-leaf varieties perform better than head types in low light.
• Asian greens: Tatsoi, mizuna, and bok choy tolerate cool conditions well.
• Kale: Baby leaves grow slowly but remain tender in winter.
• Radishes: Growable with supplemental heat or in well-insulated greenhouses.

Growers in these zones can often combine harvesting and light planting in January. Many use this month to keep greens going while preparing for heavier planting in February.

What to Grow in January: USDA Zones 8–9

Zones 8–9 include parts of the South, coastal regions, and much of the Southwest. Greenhouses here often function as frost protection rather than full winter shelters.

Expanded January Options

• Lettuce and salad mixes: Consistent production with minimal heating.
• Carrots: Slow-growing but excellent winter flavor.
• Beets: Both roots and greens are usable.
• Strawberries: Maintained for early spring flowering.

In these zones, January is often a transition month. Greenhouses help protect crops from occasional cold snaps while allowing steady winter growth.

What to Grow in January: USDA Zones 10–11

Zones 10–11 include southern Florida, southern Texas, and parts of coastal California. Winter temperatures are mild, and greenhouses are often used for wind and pest protection.

Warm-Zone January Crops

• Tomatoes: Can be grown year-round with proper ventilation.
• Peppers: Perennials in these zones when protected.
• Cucumbers: Thrive with adequate light and airflow.
• Herbs: Basil, cilantro, and parsley perform well.

In these zones, January greenhouse growing looks more like early spring in colder regions. The main challenge is managing humidity and preventing disease.

Herbs That Perform Well in January Greenhouses

Herbs are some of the most reliable January greenhouse crops across all zones. Many tolerate cool temperatures and low light better than fruiting plants.

• Parsley: Slow-growing but cold-tolerant.
• Chives: Excellent for winter harvesting.
• Cilantro: Prefers cool conditions and resists bolting in winter.
• Thyme: Hardy and low-maintenance.

Herbs often require less space and fewer inputs, making them ideal for hobby gardeners and small-scale growers during winter.

Starting Transplants for Spring

January is an excellent time to start slow-growing transplants in a greenhouse. These plants benefit from a long indoor growing period before outdoor planting.

• Onions: Seed-started onions need 10–12 weeks before transplanting.
• Leeks: Require a long season and early start.
• Celery: Slow germination and early growth.

Starting transplants early spreads the workload and allows plants to reach optimal size when spring arrives.

Common January Greenhouse Mistakes

One of the most common January mistakes is expecting summer-level growth. Low light naturally slows plants, even in heated greenhouses.

Overwatering is another frequent issue. Cold soil stays wet longer, increasing the risk of root rot. Good airflow and careful watering are essential.

Final Thoughts on January Greenhouse Growing

January is not about abundance but about consistency, protection, and preparation. A greenhouse allows growers to harvest fresh food, maintain plant health, and get a head start on spring.

By matching crops to your USDA zone and managing expectations, January greenhouse growing can be productive, rewarding, and surprisingly enjoyable.