Starting Fall Crops
As summer winds down and the days grow shorter, many gardeners turn their attention to fall planting. One of the best ways to extend your harvest into the cooler months is by growing brassicas— that hardy family of vegetables including kale, collards, broccoli, cabbage, cauliflower, and Brussels sprouts. These crops not only tolerate frost but often taste sweeter after a light chill, making them perfect for autumn gardens. Starting seedlings indoors gives you a head start, ensuring robust plants ready to face the elements. In this post, I'll walk you through the process, with a focus on timing your indoor starts for maturity around the first fall frost and tips for hardening off in late summer's lingering heat.
Why Brassicas Shine in Fall Gardens
Brassicas are cool-season champions. Unlike tender summer crops, they thrive in temperatures between 45°F and 75°F, and many varieties improve in flavor after exposure to frost. Kale and collards, in particular, are forgiving for beginners: they're nutrient-dense, pest-resistant in cooler weather, and can provide greens well into winter in milder climates. Starting them indoors protects young seedlings from summer's intense sun and heat, allowing you to transplant strong plants that establish quickly before the cold sets in.
For a fall harvest, the goal is to have mature plants by or shortly after your region's first frost date, when cooler weather enhances their growth without risking damage from extreme heat or early pests.
Timing Your Indoor Seed Starts
The key to success is backward planning from your local first fall frost date. This varies by region— for example, in our general region, it might be mid-October to early November.
Here's how to calculate:
Determine days to maturity: Most brassicas take 50-90 days from seed to harvest. Kale typically matures in 50-70 days, collards in 60-80 days, and other brassicas like broccoli or cabbage around 60-100 days. Add 10-14 days if transplanting, as seedlings need time to adjust.
Factor in transplant timing: Aim to transplant 4-6 weeks before your first frost to allow establishment. Brassicas are frost-tolerant, so they can continue growing post-frost, but you want them sizable enough to harvest before heavy freezes.
Count backward: Subtract the total days (maturity + transplant adjustment) from your frost date. For a mid-October frost, start kale or collards indoors in late July to early August. This aligns with expert advice to begin fall brassicas indoors by mid-summer for transplant in late July or August.
| Crop | Days to Maturity from Seed | Suggested Indoor Start (Weeks Before Frost) |
|---|---|---|
| Kale | 50-70 | 10-12 |
| Collards | 60-80 | 12-14 |
| Broccoli | 55-75 | 10-12 |
| Cabbage | 60-90 | 12-14 |
| Cauliflower | 50-80 | 10-12 |
| Brussels Sprouts | 80-100 | 14-16 |
Adjust for your zone: In warmer areas (USDA Zones 8+), you might start later; in cooler ones (Zones 5-6), earlier to beat shorter seasons.
How to Start Brassica Seedlings Indoors
Starting indoors is straightforward and requires minimal gear. Here's a step-by-step guide:
Gather supplies: Use seed trays or small pots with drainage, a seed-starting mix (sterile and light), grow lights or a sunny window, and a heat mat if your space is below 70°F (brassica seeds germinate best at 50-85°F).
Sow the seeds: Plant 2-3 seeds per cell, ¼-inch deep. Water gently and cover with a humidity dome or plastic wrap to retain moisture. Germination takes 7-10 days. Thin to the strongest seedling once they sprout.
Provide care: Keep soil moist but not soggy. Use grow lights for 14-16 hours daily to prevent leggy growth. Fertilize lightly with a diluted organic solution after true leaves appear. Aim for 65-75°F daytime temps.
By 4-6 weeks, your seedlings should be 4-6 inches tall and ready for the next step: hardening off.
Hardening Off in Late Summer: Acclimating Your Seedlings
Late summer can be tricky for hardening off—days are still hot, and sudden sun or wind can shock tender indoor plants. Hardening off gradually exposes seedlings to outdoor conditions over 7-10 days, building resilience. Skip this, and you risk sunburned leaves or stunted growth.
Follow this 10-day schedule, adjusting for weather:
Days 1-3: Start with 1-2 hours in dappled shade during mild mornings or late afternoons. Avoid midday sun and bring them inside if temps exceed 85°F.
Days 4-6: Increase to 3-4 hours, introducing partial sun. Water more frequently as outdoor air dries soil faster. Use a fan indoors beforehand to strengthen stems against wind.
Days 7-10: Extend to full days outside, including some direct sun. Overnight if temps stay above 50°F. Monitor for pests like aphids, which can appear during this transition.
Tips for late summer: Choose overcast days to start, and protect from intense heat with shade cloth. If you're short on time, a "lazy" method involves placing them in a sheltered spot like a porch for progressively longer periods, but don't cut corners too much—proper acclimation pays off in healthier plants.
Transplanting and Fall Care
Once hardened, transplant on a cloudy day. Space kale and collards 12-18 inches apart in rows 18-24 inches wide, in well-amended soil with compost for nutrients. Water deeply and mulch to retain moisture and suppress weeds.
In fall, brassicas need consistent watering (1 inch per week) and protection from pests like cabbage worms—use row covers if needed. Harvest outer leaves for kale and collards as needed; they can withstand frosts down to 20°F.
Wrapping Up: Enjoy Your Fall Bounty
Starting brassica seedlings indoors for fall is a rewarding way to keep your garden productive. With careful timing around your first frost and a solid hardening-off routine, you'll have vibrant, frost-kissed greens ready for soups, salads, and stir-fries. Experiment with varieties like 'Lacinato' kale or 'Georgia' collards for best results.
Cover image via pxHere - CC0 Public Domain
