Waltham 29 Broccoli From Seed: Planting and Harvest Timing

By Vego Garden | Modular Garden Beds & Smarter Growing ... | Published: 2026-11-01

Category: How-to Guides

Learn how to grow Waltham 29 broccoli from seed with the right planting window, spacing, and harvest timing for a long season of heads and side shoots.

Quick answer

Start Waltham 29 broccoli seeds indoors 4–6 weeks before your last frost, or sow directly in late summer for a fall crop. Harvest the main head while buds are tight and green, then keep cutting side shoots for weeks.

Why Waltham 29 rewards careful timing

Waltham 29 is an heirloom broccoli known for large, uniform blue-green heads and excellent flavor. Its cold hardiness lets you stretch the season, but that same trait means heat can push plants to bolt or form loose heads. The planting date matters more than almost any other factor.

Unlike hybrids bred for a single concentrated harvest, Waltham 29 keeps producing side shoots after the main head is cut. That makes harvest timing a series of decisions, not one event.

Seed-starting vs. direct sowing

Starting indoors gives you control over early moisture and temperature, which is useful if spring is wet or cold. Direct sowing works well for fall crops in mild climates, but seedlings are vulnerable to cabbage worms and slugs. If you direct sow, thin promptly to avoid competition.

Step-by-step: planting and harvest timing

1. Time your sowing: For a spring crop, start seeds indoors 4–6 weeks before your last expected frost. For fall, sow directly about 10–12 weeks before your first fall frost. Check your local frost dates rather than relying on a fixed month. Count backward from frost dates, not forward from a calendar date.
2. Start seeds at the right depth and temperature: Sow seeds ¼ to ½ inch deep in moist seed-starting mix. Keep soil around 65–75°F (18–24°C) for reliable germination. Provide bright light once sprouts appear to prevent leggy seedlings. Leggy seedlings often mean too little light, not too much water.
3. Harden off and transplant: About a week before planting out, gradually expose seedlings to outdoor conditions. Transplant when they have 4–6 true leaves and nighttime temperatures stay above 40°F (4°C). Space plants 18–24 inches apart in full sun. Cold soil below 40°F can stunt seedlings; wait for consistent warmth.
4. Water and feed consistently: Keep soil evenly moist but not waterlogged. Broccoli is a heavy feeder; side-dress with compost or a balanced organic fertilizer about 3–4 weeks after transplanting. Avoid overhead watering late in the day to reduce disease. Uneven watering stresses plants and can lead to hollow stems or poor head formation.
5. Watch for the main head: The main head is ready when buds are tight, green, and about 4–6 inches across—before any yellow flowers open. Cut the stem 4–6 inches below the head with a sharp knife. Do not wait for the head to enlarge past tight-bud stage. Yellow buds mean the head is past prime; harvest immediately.
6. Keep cutting side shoots: After the main harvest, leave the plant in place. Side shoots will develop in the leaf axils over the next several weeks. Cut them when they are 1–3 inches across and still tight. Harvest every few days to keep shoots coming. Regular cutting stimulates more side shoots; letting them flower stops production.

Product facts

Waltham 29 Broccoli Seeds: Waltham 29 is a cold-hardy heirloom that produces a large main head followed by weeks of side shoots. You can plan a longer harvest window and avoid pulling plants after the first cut.
Waltham 29 Broccoli Seeds