How to Grow Broccoli from Seed

How to Grow Broccoli from Seed: A Step-by-Step UK Guide

Growing your own broccoli is incredibly rewarding, providing fresh harvests from summer right through to the following spring. While broccoli has a reputation for being a little fussy, success comes down to two key things — firm soil and good timing. Follow this step-by-step guide to take your plants from tiny seed to a healthy, productive crop.

Phase 1: Sowing the Seeds

Broccoli can be started indoors to get a head start or sown directly outdoors once the soil warms. The method you choose depends on the variety and the time of year.

A. Sowing Indoors (For Early and Overwintering Crops)

Sowing indoors is ideal for early Calabrese (heading broccoli) and all Sprouting Broccoli varieties. It allows you to start plants safely under cover, protecting young seedlings from pests and late frosts.

• When to Sow: March–May for summer/autumn Calabrese; April–June for overwintering Sprouting varieties.
• Method: Use modular trays or small pots filled with damp, peat-free seed compost. Sow two seeds per cell about 1.5cm deep.
• Germination: Keep compost moist but not waterlogged. Germinates in 7–14 days without extra heat.
• Thinning: When seedlings form their first true leaves, remove the weaker seedling to leave one strong plant per cell.

B. Sowing Outdoors (For Later Calabrese Crops)

Calabrese can also be sown directly outdoors from April to July once the soil has warmed.

• Method: Draw a shallow drill about 2cm deep and sow thinly, or sow three seeds every 45cm in the final position.
• Thinning: Once seedlings are large enough to handle, thin to one strong plant per 45cm station.
• Seedbed Tip: If raising in a seedbed for transplanting later, thin seedlings to around 7.5cm apart to ensure sturdy growth before moving.

Phase 2: Transplanting and Planting Out

Whether raised indoors or outdoors, the goal is to plant out strong, healthy seedlings into their final growing position.

Phase 3: Ongoing Care and Protection

Once your broccoli is established, consistent care will help it thrive and produce strong heads or spears.

• Watering: Keep soil evenly moist, particularly during dry spells or when heads begin to form. Irregular watering can cause stress and lead to bolting.
• Feeding: If soil fertility is low, feed plants with a nitrogen-rich fertiliser such as pelleted chicken manure or a balanced liquid feed when they reach 20cm tall.
• Mulching: Apply an organic mulch such as compost or straw to retain moisture and suppress weeds.
• Pest Protection:
  • Cabbage White Butterflies: Use fine insect mesh or netting to prevent egg-laying and caterpillar damage.
  • Pigeons: Protect with netting or tensioned wires — pigeons can strip leaves overnight.
  • Slugs and Snails: Use traps, barriers, or wool pellets, particularly around young plants.
• Earthing Up: As plants mature, mound soil around the stems to give extra stability and prevent rocking in wind.

Phase 4: Harvesting Broccoli

Harvest timing varies between types but follows the same principle — pick heads or shoots while buds are still tight and firm.

• Calabrese (Heading Broccoli): Harvest the main head before any yellow petals appear. Once cut, side shoots will continue producing for several weeks.
• Sprouting Broccoli: Cut slender spears regularly as soon as buds form. Frequent picking encourages new shoots.
• Tenderstem / Stem Broccoli: Harvest stems 10–20cm long, before florets open. These hybrids crop continuously if picked often.
• Broccoli Raab (Rapini): Pick leafy shoots before flower buds open for the best texture and flavour.

Expert Grower’s Tip: Varieties to Stagger the Season

By combining varieties, you can enjoy a steady harvest of broccoli from early summer right through to spring:

• Early Summer: Green Magic F1 (AGM) — reliable, heat-tolerant, and slow to bolt. Also Kimono F1 for fast maturity and uniform heads.
• Late Autumn: Samson F1 — compact, cold-tolerant Calabrese that stands well through cooler months.
• Winter–Spring: Early Purple Sprouting — dependable overwintering type producing heavy crops February to April.
• Continuous Tender Stems: Delistem Green F1 — high-yielding stem broccoli with sweet, tender shoots for summer picking.

Broccoli thrives in cool, firm soil and benefits from consistent watering and good pest protection. With the right mix of varieties, you can harvest fresh broccoli nearly all year round — from quick-maturing Calabrese to overwintering Sprouting types. A little preparation goes a long way, and once established, your plants will provide one of the most rewarding harvests in the vegetable garden.