March 2, 2026

How to Grow Broccoli from Seed

Broccoli has a reputation for being difficult, but it's really not — it's just picky about temperature. It wants cool weather, consistent moisture, and rich soil. Give it those three things and you'll get heads of broccoli that make the grocery store stuff look pathetic. Miss the temperature window and you'll get a plant that bolts straight to flower before producing anything worth eating.

Here's how to grow broccoli from seed, from starting indoors through harvest.

When to start broccoli seeds

Broccoli has two planting windows in most zones: spring and fall. The fall crop is often easier because temperatures are moving in the right direction (getting cooler) rather than racing toward summer heat.

For your specific dates, check our seed starting timeline or use the planting calculator.

Starting seeds indoors

Broccoli seeds are easy to germinate. Here's what you need:

• Timing: Start 6–8 weeks before your planned transplant date
• Depth: Sow seeds ¼ to ½ inch deep in seed starting mix
• Temperature: 65–75°F for germination (seeds sprout in 5–10 days)
• Light: Once sprouted, give seedlings 12–16 hours of bright light daily. A south-facing window works; grow lights are better.
• Thinning: If you planted multiple seeds per cell, thin to the strongest seedling once they have 2 true leaves

For a complete indoor starting setup, see our indoor seed starting guide.

Hardening off

This step is critical and often skipped. Broccoli seedlings grown indoors need 7–10 days of gradually increasing outdoor exposure before transplanting:

1. Days 1–3: Set seedlings outdoors in a sheltered, shady spot for 2–3 hours
2. Days 4–6: Increase to 4–6 hours, introducing some direct sun
3. Days 7–10: Leave outdoors all day in full sun, bringing inside only if frost threatens

Skipping hardening off leads to transplant shock — stunted growth, wilting, and sometimes death. Don't skip it. See our tips on protecting plants from late frost during this period.

Transplanting broccoli outdoors

• Spacing: 18–24 inches apart, rows 24–36 inches apart. Broccoli plants get big — 2 feet wide and 2–3 feet tall.
• Depth: Plant up to the first set of true leaves (burying the stem a bit is fine and encourages stronger roots)
• Soil: Rich, well-drained, pH 6.0–7.0. Work in 2–3 inches of compost before planting. Broccoli is a heavy feeder.
• Sun: Full sun (6–8 hours minimum). Some afternoon shade is actually helpful in zones 7–8 for spring crops.

Growing and maintenance

Watering

Broccoli needs consistent moisture — 1 to 1.5 inches per week. Irregular watering causes hollow stems and small heads. Drip irrigation or soaker hoses work best. Overhead watering is fine but increases disease risk. Mulch around plants with 2–3 inches of straw or shredded leaves to retain moisture.

Fertilizing

Feed broccoli every 3 weeks with a balanced fertilizer or side-dress with compost. They're nitrogen-hungry, especially during the vegetative growth phase. Once you see the central head starting to form, back off the nitrogen slightly.

Pest management

The number one pest issue with broccoli is cabbage worms (those little green caterpillars). Here's the practical approach:

• Row covers: Floating row covers from transplant to harvest are the most effective prevention. They physically block the white cabbage moths from laying eggs.
• BT spray (Bacillus thuringiensis): An organic caterpillar-specific pesticide. Spray every 7–10 days if you see worms. It's very effective and harmless to everything except caterpillars.
• Hand-pick: Check the undersides of leaves every few days and remove any caterpillars or eggs you find.

Aphids can also be an issue. A strong spray of water knocks them off. For persistent infestations, insecticidal soap works well.

Harvesting broccoli

This is where timing matters. Harvest too early and you leave yield on the table. Too late and the head opens into yellow flowers (bolts) and becomes bitter.

When to harvest

• The central head should be firm, tight, and dark green
• Individual buds should be tightly closed — not starting to separate or show yellow
• Head size varies by variety, but most are 4–8 inches across at maturity
• Cut the stem 5–6 inches below the head with a sharp knife

Side shoots: the bonus harvest

After you cut the main head, don't pull the plant. Most broccoli varieties produce side shoots — smaller heads that grow from the leaf axils for weeks after the main harvest. These side shoots are often more tender than the main head. You can harvest them as long as the plant is healthy and temperatures stay cool.

Side shoot production is one reason fall broccoli is so rewarding — cooling temperatures extend the harvest window, sometimes for 6–8 weeks after the main head is cut.

Best varieties for home gardens

Common problems

• Bolting (flowering before heading): Caused by heat stress. Broccoli heads form best at 60–70°F. If temps consistently exceed 80°F, the plant may bolt. This is why fall planting is often more reliable than spring.
• Tiny heads: Usually from transplant stress, inconsistent watering, or insufficient nutrients. Make sure plants aren't root-bound when you transplant them.
• Hollow stems: Caused by rapid growth with too much nitrogen and not enough boron. You can add borax to the soil (1 tablespoon per 100 sq ft) but this is rarely necessary with good compost.
• Purple tinge on leaves: Phosphorus deficiency or cold stress. Usually resolves on its own as soil warms.

Companion plants for broccoli

Good companions include onions, garlic, beets, celery, and herbs like dill, chamomile, and rosemary (which help repel pests). Avoid planting near tomatoes, peppers, or strawberries. For a complete guide, see our companion planting chart.