How to Grow Broccoli

How to Grow Broccoli

Broccoli plants are easy to grow brassica plants, making them a fantastic choice for any gardener. These vegetable plants are packed full of flavour, with home-grown varieties offering much more interesting flavours and colours as opposed to supermarket-bought varieties. In fact, broccoli can produce both purple and white florets in addition to their well-known green colour.

If you’re eager to try growing broccoli out for yourself, the simple process makes these vegetables a very worthwhile addition to your growing space. Below, you can find our complete guide on how to grow broccoli and calabrese to get started, with expert tips on each stage of growing, from sowing right through to harvesting.

Broccoli vs Calabrese

Though broccoli and calabrese are sometimes used interchangeably, these two types of vegetables are slightly different. What is referred to as ‘broccoli’ in supermarkets is calabrese broccoli, which is known for its large, central head. Broccoli (or sprouting broccoli) within a gardening context refers to plants that grow long, leafy stems and produce small clusters of edible buds.

Both are grown very similarly, however, there lies a couple of differences in their growth. Calabrese broccoli is faster to mature, generally taking somewhere between three to four months. However, sprouting broccoli can take from four to ten months to mature. Calabrese broccoli is thereby better suited for summer and autumn harvests while sprouting broccoli is suited for overwintering.

The following guide includes growing tips for both sprouting and calabrese broccoli.

Ground Prep

Broccoli should be grown in fertile, firm soil in a sunny, sheltered spot. Shelter is important for sprouting broccoli, as this helps to protect against strong winds.

Prepare your beds with a good amount of well-rotted manure or garden compost. It’s better if this has been done several months in advance, as this means that the ground will have had time to settle. However, it can be added beforehand by firming the soil down by treading, then raking to ensure its smooth.

Broccoli prefers slightly alkaline soil, so add some lime soil conditioner if your soil is more acidic. Ideally, this is best done the previous winter. You should also enrich the soil by adding some high potassium fertiliser before planting

Be sure to avoid planting broccoli in a bed where you’ve grown brassicas within the past two years, as this can lead to your plants developing diseases. Instead, practice good crop rotation by growing plants from different vegetable families in your beds each year. 

Sowing

How to Sow Broccoli Seeds

Sowing broccoli seeds can be done either indoors or outdoors depending on when you would prefer to grow it. Below are tips on how to sow broccoli seeds and calabrese seeds using either methods.

Sowing Broccoli Seeds Indoors

You can sow broccoli seeds indoors between February and April for calabrese varieties and between March and June for sprouting broccoli. The timeframe for sowing calabrese is smaller as it doesn’t transplant very well once the weather gets warmer.

To sow broccoli indoors, either keep your seeds within a greenhouse or keep them on a sunny windowsill. Starting your seedlings indoors offers a couple of benefits in comparison to outdoor sowing, as it provides protection from pests attacking your seedlings, protection against harsh weather conditions and an earlier harvest.

Sow your seeds in seed trays with two seeds per module in seed compost, watering well and sowing 2cm (¾in) deep. Your seedlings should germinate within two weeks. When they do so, thin out the weaker seedling in the module, leaving just the strongest one. After this, ensure they’re watered regularly, receive a good amount of light and are given a liquid fertiliser once every week.

Once your plants are 10–15cm (4–6in) tall and have four or five true leaves, they will be ready for transferring outside.

Sowing Broccoli Seeds Outdoors

You can sow broccoli seeds outdoors between April and June, either in seedbeds for transplanting later or in their final position. However, calabrese varieties should generally be sown in their final position after April as they don’t respond well to transplanting in warmer weather. Before sowing, create a shallow drill that’s around 2cm (¾in) deep and water it prior to sowing.

For sowing your seeds in a seedbed, they should be sown very thinly at about 7.5cm (3in) apart. Alternatively, you can thin your seedlings out to this spacing if you’ve sown more thickly.

For sowing in their final position, sow three seeds every 60–80cm (24–30in) for sprouting varieties or every 30cm (1ft) for calabrese varieties. Spacing requirements may vary depending on the variety of broccoli you grow, so check your seed packet for more specific instructions. Once they germinate, thin these out so that just one strong seedling remains.

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Planting

When to Plant Broccoli Plants

Your broccoli plants should be transplanted between April and July for sprouting varieties while calabrese varieties should be planted out between April and June, before warm weather begins. They should be planted out once they are between 10-15cm (4-6in) high.

How to Plant Broccoli Plants

Your broccoli plants should be transplanted after first being gradually hardened off for a couple of weeks to get them used to outdoor conditions.

Sprouting broccoli will require around 60–80cm (24–30in) between individual plants and rows, while calabrese broccoli requires about 30cm (1ft) apart, with 45cm (18in) between rows. However, their most preferable spacing measurements can change for different varieties of broccoli, so check your seed packet for specific advice. A good amount of space ensures plants can grow to their full potential and have good air circulation to reduce the risk of disease.

When transplanting, take good care not to disturb the roots, as this can impact growth, and water well before and after planting. Plant your plants deeper than they were previously growing to allow them to root deeply so that their lowest leaves are at the surface. Ensure you plant your broccoli plants securely and firm them in very well, as calabrese can suffer from windrock if the soil is loose.

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Plant Care

Watering

Water your broccoli plants regularly when they are seedlings and young until they are well established. Afterwards, they will only need watering occasionally during dry weather, roughly once every fortnight.

Feeding

Once your plants reach around 20cm (8in) in height, feed them with a high-nitrogen feed as recommended per your chosen feed’s instructions to encourage growth.

Mulching

Adding a good layer of garden compost over the soil of your broccoli plants will help to prevent weed growth and retain moisture.

Support

Broccoli plants can suffer from windrock due to being top-heavy, so will need extra support. For sprouting broccoli varieties, adding a sturdy cane to the soil will keep them more secure. For both sprouting and calabrese varieties, piling up soil around the stem for extra security is a beneficial step.

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Harvesting

When to Harvest Broccoli

Broccoli can take anywhere from three to ten months to grow depending on various factors, such as the variety you grow and when you grow it. Calabrese broccoli will be faster to mature and will be ready between late summer and mid-autumn. Sprouting broccoli will provide harvests over a longer period, from mid-summer to the next spring. Broccoli is ready to harvest once the heads are well formed but still in bud.

How to Harvest Broccoli

To harvest sprouting broccoli, cut the main spear first, cutting at the base and for around a 10cm (4in) stem. After cutting the main head, side shoots will develop which you can harvest over the next few weeks. Check your plants regularly as the more you harvest, the more they’ll produce. To harvest calabrese broccoli, you cut the main head when it’s tight and firm, but before their flowers begin to open as they can become bitter and tough after this point. Be sure to harvest them as soon as they’re ready, as flowers can open quickly in warmer weather. Like with sprouting broccoli, you can harvest the side shoots that then start growing in the following weeks.

Problems

Broccoli is generally a straightforward vegetable to grow and doesn’t pose a great deal of problems. There are one or two issues that can affect your plants, though these are either prevented or resolved using the methods below:

Birds - Birds, such as pigeons, can be known to attack broccoli plants. This can be prevented by growing them under garden netting for protection.

Pests - Various pests can attack broccoli, including cabbage root fly, cabbage caterpillars, slugs, and snails. You can protect your plants by using a range of measures, such as insect-proof netting and slug and snail control products.

Bolting - Broccoli plants can bolt if exposed to high temperatures, which diverts energy away from growing compact heads and instead into flowers. Preventive measures include growing bolt-resistant varieties and refraining from overwatering winter varieties so that they better adjust to hotter temperatures.

Clubroot - Clubroot is a disease which causes plants to form severely distorted and swollen roots. This then leads to poor nutrient and water absorption and poor growth. Clubroot is not able to be chemically removed, so preventative measures are the best solution. This includes buying disease-resistant vegetable seeds, growing seeds from trusted providers and practising good garden hygiene. For more information on clubroot, read our guide on how to prevent clubroot disease.

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Shop Broccoli Seeds and Plants at D.T. Brown

Now that you know how to grow calabrese and sprouting broccoli, you can get started on growing your own broccoli seeds and broccoli plants by shopping from our quality range. At D.T. Brown, you can find these, in addition to calabrese seeds, in a range of different cultivars for dependable growth and distinct flavours. We have over a century of experience in providing gardeners with superior seeds and plants, so you can shop our collection with confidence.

If you’re interested in learning how to grow even more vegetable seeds and fruit seeds, take a look at our many other growing guides and insightful blogs on our garden blog. You can also browse our guide on how to grow brassicas for more general tips, where you can also find further specified brassica growing guides such as this one.

If you have any questions about our range of garden accessories, herb seeds, flower seeds, or anything else on our site, contact us today and a member of our team will be happy to help you.

Pim Dickson

Plant Expert

When Pim joined D.T. Brown, it was originally as a seed buyer, but now as our planting & sowing expert, he’s responsible for all horticultural and technical content, sharing his expertise in this catalogue, and through the growing advice and tips on our seed packets.

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Guide Chapters

Guide Chapters

  • How to Grow
  • Ground Preparation
  • Sowing
  • Planting
  • Plant Care
  • Harvesting
  • Problems

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