A Complete Guide to Sowing, Growing and Harvesting Broccoli Seeds
Broccoli is one of the most rewarding vegetables to grow in Ireland. Our cool, moist climate is ideal for this nutritious brassica, allowing gardeners to produce high-quality harvests with relatively little effort. Whether you're growing traditional purple sprouting broccoli for winter harvests or faster-maturing summer varieties, careful timing is the key to success.
Why Broccoli Grows Well in Ireland
Broccoli thrives in cool conditions and struggles in prolonged heat. Ireland's temperate climate provides ideal growing conditions, helping plants develop tender stems and tightly packed flower buds. Commercial broccoli is grown extensively throughout Ireland, with the main harvesting season running from July to March.
In addition to being productive, broccoli is rich in vitamins C and K, fibre, antioxidants and beneficial plant compounds.
Choosing a Type of Broccoli
There are two main types commonly grown by home gardeners:
Purple Sprouting Broccoli
- Traditional Irish and British favourite
- Sown in spring or early summer
- Harvested from late winter to early spring
- Produces many side shoots over several weeks
Calabrese (Green Broccoli)
- Produces a large central head
- Faster growing
- Harvested in summer and autumn
- Better suited to gardeners wanting a quicker crop
When to Sow Broccoli in Ireland
The sowing window depends on the type you are growing.
| Type | Sow Indoors | Sow Outdoors | Harvest |
|---|---|---|---|
| Calabrese | February–May | April–June | July–October |
| Purple Sprouting Broccoli | March–June | April–July | February–April (following year) |
For the longest harvest season, sow small batches every few weeks from spring through early summer.
Starting Seeds
Sowing Indoors
- Fill modular trays or small pots with seed compost.
- Sow seeds approximately 1cm deep.
- Keep at 15–20°C.
- Seeds usually germinate within 5–10 days.
- Grow seedlings on until they have 4–6 true leaves.
Sowing Outdoors
From April onwards, seeds can be sown directly into a prepared seed bed.
- Sow 1cm deep.
- Space rows 15cm apart.
- Keep moist during dry periods.
- Thin seedlings as they grow.
Preparing the Soil
Broccoli is a hungry crop and benefits from fertile soil.
Before planting:
- Incorporate well-rotted compost or manure.
- Choose a sunny or lightly shaded location.
- Ensure good drainage.
- Aim for a soil pH of around 6.5–7.5.
As a member of the cabbage family, broccoli benefits from crop rotation and should not be planted repeatedly in the same location.
Planting Out
Transplant seedlings when they reach approximately 10–15cm tall.
Spacing:
- Calabrese: 45cm apart
- Purple sprouting broccoli: 60cm apart
Firm plants well into the soil. Brassicas grow best when planted firmly, reducing the risk of wind rock and poor root establishment.
Caring for Broccoli
Watering
Keep plants consistently moist, especially during dry spells. Uneven watering can reduce head quality.
Feeding
Apply a nitrogen-rich organic feed or liquid seaweed feed every few weeks during active growth.
Pest Protection
The most common problems include:
- Cabbage white caterpillars
- Pigeons
- Aphids
- Slugs on young plants
Fine insect mesh or netting provides excellent protection from both butterflies and birds.
Supporting Plants
Purple sprouting broccoli remains in the ground through winter and may require staking in exposed locations.
When to Harvest
The most important rule is to harvest before the flower buds open.
Calabrese
Harvest the central head when:
- The head is fully formed.
- Buds are tight and compact.
- No yellow flowers are visible.
Cut approximately 10cm below the head.
After harvesting the main head, smaller side shoots will continue to develop for several weeks.
Purple Sprouting Broccoli
Harvest individual spears when:
- Flower buds are well formed.
- Buds remain tightly closed.
- Stems are tender and succulent.
Regular picking encourages more shoots to develop.
Harvest Calendar for Ireland
| Month | Activity |
| February | Start early indoor sowings |
| March | Sow indoors or under protection |
| April | Begin outdoor sowing |
| May | Continue sowing and transplanting |
| June | Final sowings for many varieties |
| July | First harvests of summer broccoli |
| August | Main harvests continue |
| September | Continue harvesting |
| October | Late calabrese harvests |
| November–January | Purple sprouting broccoli develops |
| February–April | Harvest purple sprouting broccoli |
Common Mistakes to Avoid
Harvesting Too Late
Once buds begin opening into flowers, quality declines rapidly. Check plants regularly and harvest promptly.
Planting Too Close Together
Crowded plants produce smaller heads and suffer more pest problems.
Poor Soil Fertility
Broccoli requires fertile soil and regular feeding for the best yields.
Lack of Pest Protection
Many gardeners lose crops to cabbage white caterpillars. Protective netting is often the simplest solution.
Final Thoughts
Broccoli is one of the best vegetables for Irish gardens. With sowings from spring through summer, you can enjoy harvests from midsummer right through to the following spring. Purple sprouting broccoli is particularly valuable, providing fresh vegetables during the hungry gap when few other crops are available.
By sowing at the right time, planting into fertile soil and harvesting while buds remain tight, Irish gardeners can enjoy abundant harvests of this highly nutritious crop year after year.