September marks a perfect transition time for California gardeners to start new greenhouse crops. The cooling temperatures combined with ample sunshine create ideal growing conditions for many vegetables and herbs.
Getting these plants established now means you’ll enjoy fresh harvests throughout fall and winter when outdoor gardens slow down.
1. Leafy Spinach
Spinach thrives in September’s cooler greenhouse environment, especially in regions like California where mild fall temperatures support consistent growth. This nutritional powerhouse grows quickly from seed to harvest in about 40 days.
Plant seeds half an inch deep in rich, well-draining soil. Space rows about 12 inches apart to allow proper air circulation. The controlled greenhouse temperature prevents spinach from bolting too quickly, giving you tender leaves for months.
2. Rainbow Swiss Chard
The vibrant stems of rainbow chard bring a splash of color to your greenhouse garden. Hardy and productive, chard continues growing as you harvest outer leaves.
Sow seeds directly in well-composted soil about half an inch deep. Water consistently but avoid wetting the leaves to prevent disease. The greenhouse protection means you’ll be harvesting these beautiful nutritional giants all winter long.
3. Crisp Lettuce Varieties
Nothing beats homegrown lettuce for freshness! In places like California, September greenhouse planting means continuous salad harvests through winter.
Try butter, romaine, and oak leaf varieties for diversity. Plant seeds just ¼ inch deep, barely covering with soil. The greenhouse environment prevents frost damage while maintaining the cool temperatures lettuce loves.
Harvest outer leaves as needed to extend your crop’s productive life.
4. Aromatic Cilantro
Cilantro often bolts quickly in summer heat, making greenhouse fall planting perfect. The controlled environment keeps temperatures ideal for leaf production rather than flowering.
Sow seeds directly where they’ll grow, as cilantro dislikes transplanting. Keep soil consistently moist but not waterlogged. Greenhouse growing extends your harvest season substantially.
For continuous supply, plant new seeds every three weeks.
5. Gourmet Radishes
Radishes reward impatient gardeners with incredibly fast results – some varieties mature in just 21 days! Their peppery crunch adds zip to fall salads, and in California greenhouses, they thrive well into fall.
Sow seeds directly in loose soil about ½ inch deep and 1 inch apart. The greenhouse environment prevents the soil from getting too cold, which can make radishes woody.
Try colorful varieties like watermelon radish or French breakfast for visual appeal.
6. Tender Green Onions
Green onions make perfect space-saving greenhouse crops. They grow quickly and can be harvested multiple times by cutting what you need while leaving roots intact.
Plant seeds ¼ inch deep in rich soil or try regrowing from store-bought green onion bottoms. The greenhouse protection means continuous growth even during winter months.
For maximum flavor, harvest in the morning when essential oils are most concentrated.
7. Snap Peas
Sweet, crunchy snap peas climb upward, maximizing your greenhouse space. California growers especially value their vertical habit, which leaves room for other crops below.
Install trellises before planting seeds 1 inch deep and 2 inches apart. The greenhouse environment protects tender pea shoots from frost while providing ideal growing temperatures.
Harvest pods when they’re plump but before seeds fully develop for the sweetest flavor and crispest texture.
8. Asian Greens
Bok choy, tatsoi, and mizuna grow rapidly in greenhouse conditions. These nutritional powerhouses add variety to your winter meals with unique flavors and textures.
Sow seeds ¼ inch deep in nutrient-rich soil. Most Asian greens can be harvested as baby leaves in just 21 days or grown to full size.
The greenhouse protection prevents cold damage while maintaining the cool temperatures these greens prefer.
9. Fresh Basil
Extend your basil season by moving production to the greenhouse in September. In California, where fall nights can cool quickly, greenhouse basil thrives while outdoor plants suffer.
Start with transplants or sow seeds ¼ inch deep in warm soil. The controlled environment prevents the cold damage that quickly kills outdoor basil.
Pinch growing tips regularly to encourage bushy growth and prevent flowering for the most flavorful leaves.
10. Colorful Carrots
Rainbow carrots bring excitement to the dinner table! Purple, red, yellow, and white varieties grow beautifully in deep greenhouse containers.
Sow seeds in loose, stone-free soil at least 12 inches deep. The greenhouse environment keeps soil temperatures consistent for better germination. Space seeds about ½ inch apart, then thin to 2 inches as they grow.
Harvest when shoulders reach desired diameter for sweetest flavor.
11. Baby Kale
Baby kale offers milder flavor than mature leaves while packing the same nutritional punch. In California greenhouses, the environment keeps plants producing tender new growth throughout winter.
Sow seeds ¼ inch deep in rich soil. Begin harvesting outer leaves when plants reach 4 inches tall.
Unlike outdoor kale that gets sweeter after frost, greenhouse kale maintains consistent flavor and texture. For continuous harvest, plant new batches every 3–4 weeks.
12. Microgreens Mix
Microgreens deliver intense flavor and nutrition in tiny packages. These seedlings of vegetables and herbs are harvested when just 1-3 inches tall.
Sow seeds densely in shallow trays filled with sterile seed-starting mix. The greenhouse environment provides perfect conditions for fast, clean growth.
Most varieties are ready to harvest in just 7-14 days, making them the fastest crop you can grow for continuous fresh greens.
13. Bush Cucumbers
Compact bush cucumber varieties fit perfectly in greenhouse environments. Unlike their sprawling garden cousins, these space-savers grow upright with minimal support needed.
Plant seeds 1 inch deep in rich, well-draining soil or start with transplants. The greenhouse protection extends your cucumber harvest well into fall and winter.
Hand-pollinate flowers with a small brush for best fruit set since natural pollinators may be scarce.