Having a greenhouse can be a significant game-changer in the fall, particularly for gardeners living in colder climates. A greenhouse allows you to extend the growing season by protecting tender crops. It can also help you to get a head start on winter or spring harvests.

September is an excellent time to get those cool-weather crops planted. What you can grow depends on your climate and whether you have a heated or unheated greenhouse. You should also consider whether you want long-term overwintering crops or those with fast harvests. 

A good rhythm to aim for when planting in September is to pair quick-growing crops with slower overwintering types. This way, you have crops to harvest in fall and early winter, as well as late winter and early spring. In milder climates, even an unheated greenhouse can make growing vegetables year-round a possibility. 

Everyone knows that leafy greens perform well in winter, and your greenhouse will support them well during this time. There are many other delicious vegetables and herbs that also favor cool weather, though. Let’s talk about some September greenhouse crops alongside those greens for a continuous harvest. 

Kohlrabi ‘Purple Vienna’

Quick-growing bulbs with crisp, nutty flavor.

Kohlrabi is an excellent September greenhouse crop (and it’s good for planting even later, too). It loves cool temperatures, matures quickly, and produces a crop of sweet, crisp, tasty bulbs. You can also eat the green tops. Their ideal temperature range is 55 to 75°F (13-24°C). 

‘Purple Vienna’ is a lovely crop. Large, purple, and crisp, it has a sweet, nutty, and slightly peppery flavor. You can eat them raw or cooked, and there are many ways to prepare them. Kohlrabi is an excellent source of vitamin C. Try shredding the bulb-like portions of the stem and using it in a stir fry!

Radish ‘French Breakfast’

Fast harvests with steady succession sowing.

It’s exceptionally easy to grow this fast crop in your greenhouse in September. Radishes are one of the quickest vegetables you can grow, and they love cool weather. Succession sow your radishes, planting every two to three weeks for a continuous harvest throughout the fall and winter months. 

‘French Breakfast’ is a long-loved heirloom that dates back to the 1800s. It has a delicious, delicate flavor, and it’s pretty, too! Even in warmer climates, you can get this crop started in September, as ‘French Breakfast’ is more heat-tolerant than most varieties. 

Beet ‘Robin’

Sweet baby roots that resist bolting.

Beets are great September greenhouse crops. These cool-season root vegetables thrive in the steady conditions of a greenhouse. Beets produce a double crop, as you can eat both the tender, nutrient-dense greens as well as the earthy roots. You can succession grow these, just like radishes, for a steady harvest through fall and winter.

‘Robin’ beets are a perfect variety for harvesting in the baby stage. They have tender, sweet, crisp roots with a deep red color. They grow uniformly round at an early stage and have high bolt resistance. So, if the weather warms up unexpectedly, these shouldn’t bolt as easily as other types. 

Carrot ‘Danvers 126’

Sweet roots thrive in cool greenhouse conditions easily.

Carrots are a perfect crop for growing in your greenhouse in September. They like cool weather, and the protection from temperature swings is a major benefit of greenhouse growing. Growing them this way will bring you sweet, crisp roots well into the winter months. 

‘Danvers 126’ is a delicious heirloom variety that dates back to the late 19th century. They are bright orange with a uniform shape and size, and are highly productive. Carrots can be slow to germinate, but these will be reliable. They can take up to 20 days to sprout, so be patient with this crop.

Turnip ‘White Lady’

Ready in just 30 days with tender greens.

Growing turnips in a greenhouse is a simple way to enjoy this cool-season crop well into fall and winter. Because they thrive in moderate temperatures, the greenhouse environment protects them from extreme cold. Direct sowing is important with all root vegetables for well-shaped roots. Regular watering is important too, as dry spells can make the roots woody,

In just 30 to 60 days (depending on the variety), you can harvest tender, crisp roots. ‘White Lady’ is a fast grower, and you can harvest the roots along with nutritious greens in about 30 days. These are great for eating young, in the baby stage. 

Green Onion ‘Tokyo Long’

Succession sow for mild stalks all season.

Growing green onions in a greenhouse is an excellent way to keep a supply of this crop for the kitchen. You’ll have fresh, flavorful stalks through the cooler months if you plant them in September. These alliums thrive in temperatures between 55 and 75°F (13-24°C). They’re well-suited to the protected environment of a greenhouse during the colder months. 

‘Moss Curled’ parsley is a cold-tolerant variety with a mild flavor. It’s also decorative with its attractive, curling leaves. Regular watering is key, as parsley doesn’t like to dry out, but be careful to avoid waterlogging. With steady care, you can harvest outer leaves continually. This allows the plant to keep sending up fresh growth for many months. 

Cilantro ‘Long Standing Santo’

Slow-bolting plants for longer harvests.

Cilantro is a quick-growing herb that does especially well as a September greenhouse crop. This crop prefers temperatures between 50 and 70°F (10-21°C) and tends to bolt quickly in summer heat. Direct sowing is best, as cilantro develops a long taproot, so it doesn’t transplant well.   

‘Long Standing Santo’ has wonderful flavor and attractive leaves. It’s slow to bolt, so you don’t need to worry about unexpectedly warm weather. In the controlled environment of a greenhouse, you can manage temperature swings and extend its productive season. Space plants six inches apart in well-drained soil, and keep them consistently moist to encourage lush leaf growth. 

English Thyme

Drought-tolerant herbs need only occasional careful watering.

English thyme is an ideal perennial herb for greenhouse growing in September, especially in the fall and winter. It’s fairly frost-tolerant, but in cooler climates, outdoor conditions may be too harsh for steady production.

This Mediterranean plant thrives in well-drained, sandy soil and prefers moderate temperatures between 55 and 70°F (13-21°C). A greenhouse provides the right conditions consistently for these September crops. 

English thyme is invaluable in the kitchen. The plant is aromatic and attractive, and the tiny, delicate leaves are savory and delicious. Once rooted, space plants 12 to 18 inches apart, as they form low, spreading mats of aromatic foliage. Thyme is drought-tolerant by nature, so in the greenhouse it’s important not to overwater. Allow the soil surface to dry slightly between waterings to prevent root rot. 

Common Oregano

Prefers drier soil with good airflow.

Oregano is a sun-loving September greenhouse crop that adapts nicely. It’s especially successful during the cooler fall and winter months. Planting this crop in your greenhouse in September is ideal. It benefits from protection against frost and excess rain.

In a greenhouse, it thrives in well-drained, sandy or loamy soil with a slightly alkaline pH. It prefers temperatures between 55 and 75°F (13-24°C) to keep it productive. 

Starting your oregano plants from cuttings or small transplants establishes them much faster. Space them about 12 inches apart to allow for their natural spreading habit. Oregano prefers drier conditions, so it’s best to water sparingly. Allow the top inch of soil to dry between waterings. Good airflow is imperative to prevent fungal problems. 

Rosemary

Best grown in containers for easy moving.

Rosemary is a warm-climate, perennial herb, so growing it in cool climates is tricky. A greenhouse is ideal for growing this tasty herb. It’s good to grow your rosemary in a container that is movable. You’ll want to move it outdoors for the warmer months. In zones 7 and south, you can grow it outdoors as an evergreen. 

In cool regions, rosemary will benefit from the consistent temperatures in the greenhouse. It likes sandy, gritty soil and is prone to root rot, so be careful not to overwater. This September greenhouse crop appreciates air circulation as well. 

Broccoli ‘Belstar’

Heat-tolerant heads with plenty of side shoots.

Broccoli is a great September greenhouse crop, especially in regions with unpredictable autumn weather. Fluctuations in temperature can result in unsteady growth. It will overwinter well in a greenhouse in cooler-than-usual climates. Direct seed your broccoli in deep beds, or transplant to about 12 inches apart if you start seeds in trays. 

‘Belstar’ has good heat tolerance, so it’s great in unpredictable climates. You’ll be able to germinate the seeds in warmer climates without waiting for the temperature to drop. One central head will grow at the top, and many side shoots make for an extended harvest. 

Brussels Sprouts ‘Silvia’

Harvestable sprouts appear after a long, steady season.

Brussels sprouts have a longer growing season than other brassicas, so they require a bit of patience. They’re cool-weather crops that thrive in the consistent temperature that a greenhouse provides. Planting them in September will give you a crop to harvest in December. 

‘Silvia’ produces earlier than the average sprout, though it can be difficult to grow. It has great disease resistance, however, and produces many tasty Brussels sprouts.