Must-Grow Fall Crops for a Thriving Greenhouse Harvest

As the days get shorter and temperatures start to dip, many gardeners pack up their tools and say goodbye to fresh produce until next spring. But with a greenhouse, you can extend your growing season well into the fall and beyond! The key to successful greenhouse growing in the "shoulder season" (the time between summer and winter) is choosing the right crops and making a few simple adjustments to your gardening routine.

Here’s a guide to the best fall crops for greenhouse growing and tips for success during this transitional season:

Best Fall Crops for Greenhouse Growing

Fall is the perfect time to grow cool-weather crops that thrive in lower temperatures and shorter daylight hours. Here are some of the best vegetables and herbs to plant in your greenhouse this season:

Leafy Greens

• Lettuce: Hardy and fast-growing, lettuce varieties like romaine, butterhead, and leaf lettuce do well in cooler temperatures.
• Spinach: Spinach is cold-hardy and grows quickly, providing a continuous harvest throughout fall.
• Kale: Kale can withstand cold temperatures and actually tastes sweeter after a frost.

Root Vegetables

• Carrots: Carrots thrive in cooler weather, and greenhouse protection helps them grow through the fall.
• Radishes: These fast-growing vegetables mature in as little as 4 weeks, making them a great fall crop.
• Beets: Beets can tolerate cooler temperatures and are perfect for shoulder-season growing.

Brassicas (Cabbage Family)

• Broccoli: With a little extra care, broccoli can produce in cooler temperatures and bring a bountiful harvest.
• Cauliflower: Cauliflower is a bit more delicate, but growing it in a greenhouse can extend its growing period.
• Brussels Sprouts: These hardy plants love cooler weather and grow well into the fall.

Herbs

• Cilantro: This herb thrives in cooler temperatures, making it perfect for fall growing.
• Parsley: Another cold-tolerant herb, parsley grows slowly but steadily throughout the cooler months.
• Chives: Hardy and easy to grow, chives add fresh flavor to fall dishes and salads.

The Old Farmer's Almanac provides a detailed guide on frost-tolerant crops and planting schedules for fall gardening, including crops like kale, broccoli, and spinach, which are great for greenhouse growing in the cooler months​.

The Prairie Homestead offers insights into hardy vegetables like leeks, cabbage, and turnips that thrive in fall, along with tips on cold-weather care and mulching​.

Greenhouse Info lists top greenhouse crops for autumn, including beets, carrots, and arugula, which are perfect for extending your harvest into fall​.

Tips for Success During the Shoulder Season

Greenhouse growing in the fall requires some adjustments to ensure your crops thrive as the weather cools. Here are a few tips to keep your greenhouse productive:

Maximize Sunlight Fall brings shorter days, so it’s important to maximize the sunlight your plants receive. Keep your greenhouse clean by washing the walls and removing any dust or debris that might block light. Positioning reflective surfaces inside can also help bounce more sunlight onto your plants.

Monitor Temperature Even though greenhouses help retain heat, the drop in outdoor temperatures means you need to be mindful of nighttime lows. Install a thermometer to monitor the temperature and consider using a small space heater or heat mats to keep plants warm on especially cold nights. Keeping the temperature around 55-65°F (13-18°C) is ideal for most fall crops.

Improve Ventilation While keeping your greenhouse warm is important, so is airflow. Good ventilation reduces the risk of mold and disease. Open vents or use fans to maintain air circulation, especially on sunny days when temperatures inside can spike.

Water Wisely As temperatures cool, plants need less water. Overwatering can lead to root rot and other issues. Check the soil moisture regularly, and water in the morning so plants can absorb moisture during the day and dry out before the cooler nights.

Use Row Covers for Extra Protection In colder regions, or if an unexpected frost hits, adding row covers or frost cloths inside your greenhouse can offer an additional layer of protection for your plants. Row covers help retain warmth and create a microclimate that can extend the growing season even further.

Fertilize Less During the shoulder season, plants grow more slowly due to cooler temperatures and less sunlight. Reduce your fertilizing schedule, as over-fertilizing can lead to excess growth that isn’t sustainable as temperatures drop.

Plan for a Winter Harvest

One of the best parts of fall greenhouse gardening is that it can set you up for a winter harvest. By planting cold-tolerant crops now, you’ll be able to continue harvesting fresh produce throughout the winter. Many fall crops, like kale and spinach, will overwinter and provide fresh leaves even in the coldest months.

Happy Gardening!