Two Wests & Elliott's Gardening Guide To Growing Broccoli (Calabrese)
Before we start talking about growing broccoli, we first need to explain about the relationship between broccoli and calabrese . . . as those canny gardeners amongst you may have realised that the images you are seeing in this growing guide show calabrese. It’s all down to most supermarkets referring to calabrese as broccoli, which has made us familiar with this big, green headed vegetable being called ‘broccoli’ – when technically it’s calabrese!
Broccoli and calabrese are actually two varieties of the same vegetable, however calabrese has a much faster maturing rate compared to broccoli, which is why supermarkets tend to market both varieties as ‘broccoli’ as it helps them cater to year-round demand.
So, in this guide we are talking about what we all think of as broccoli (calabrese) - with the lovely green heads - rather than sprouting broccoli which has heads of purple or white - sprouting broccoli will be covered in another guide.
Selecting The Seeds For Growing Broccoli
With many varieties of broccoli to choose from, with different sowing and harvesting time, from traditional varieties which tend to be slow growing through to more modern varieties which have been bred to be more compact and faster growing. So take your time and study the different seeds available online and choose those which will suit your space, when you want to sow or harvest and the style of the head.
Broccoli varieties we recommend include:
Green Magic F1 – a lovely, dark green variety with very smooth, tightly packed heads. An early maturing variety with great flavour. Can be sown indoors from March for harvesting from July.
Marathon F1 – with dark blue / green florets this variety is disease-resistant making it ideal for new growers. Sow indoors from February for harvesting from June onwards.
Monclano F1 – this robust variety is resistant to both clubroot and mildew. With tight domed head it produces heavy crops with excellent flavour. Sow indoors from April for harvesting from August onwards.
Fiesta F1 – with strong stems and high-quality, solid heads, this variety is an excellent choice for spring or summer sowing. Sow indoors from March for harvesting in June / July.
Kabuki F1 – with short, compact plants with deep, well rounded, green heads, this variety will take up less space. Sow indoors from mid-February for harvesting from July onwards.
Preparing The Ground For Growing Broccoli
Depending on the variety of broccoli you have chosen to grow will affect the amount of space you need at your allotment or in your kitchen garden to grow it – so always check the seeds packet first for guides on spacing the plants when planting out. However, what we do know (and you will read this later in our guide – under transplanting broccoli) broccoli likes space in which to grow and produce healthy, bumper crops, so you are looking for a space suitable in size, which is also sheltered from strong winds (just because some broccoli plants can grow quite tall).
Once you have the space chosen ideally you should prepare the ground at the end of Autumn, so it has time to settle before you start using it. Broccoli likes to be grown in soil with a pH of 6 to 7 so use a soil testing kit to measure the soils pH and if necessary, adjust an acidic soil by using lime to get to the pH required.
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Using a soil testing kit is a great way of testing your soil for a range of properties which will affect plant growth – so not only pH, but also phosphorus, nitrogen, and potash. This kit has sufficient chemicals for approx. 60 tests so you can test the soil, make a change – in our case for broccoli that could be adding lime – then retest the soil three months later to check the changes and amend again if required. Click here to see full details. |
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When preparing the ground you should make sure it is packed with nutrients by digging in some well-rotted manure or garden compost. If you can’t add manure or compost you are best to boost the nutrients by using a high potassium general fertiliser.
Apart from growing best in a nutrient rich soil, broccoli will also benefit from being grown in a firm, well-draining soil which is in the sun (or partial shade).
When To Sow Broccoli Indoors
Sowing broccoli seeds indoors rather than outdoors is good for two reasons:
- It allows you to sow early, so you get an early harvest
- It allows your plants to develop a healthy root system before being transferred into the ground – this is especially important if you have clubroot disease in your soil as this means they will be less affected by it.
You can start to sow broccoli indoors from mid-February onwards, and if you want to be able to harvest crops regularly over a long period rather than all the plants being ready to harvest at once, then sow small batches every couple of weeks.
Top Tip
We always recommend checking the seed packet for precise details on when to sow – different varieties of broccoli will have been developed to be sown earlier or later in the year.
As you are sowing the broccoli seeds with the intention of transplanting them later, to avoid damage to their roots they are best sown in modular trays, so their roots have their own space to grow and don’t become entangled with their neighbours’ roots. Usually, you would sow two seeds per module and then thin back to just the strongest seedling when they start to grow. It should take about two weeks from sowing the seeds for them to germinate (when not provided with extra heat by starting them in a propagator or on a heated tray).
They should be grown in good natural light, watered regularly and given a weekly feed with a general-purpose fertiliser.
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Your broccoli plants will be staying indoors until they are at least 4 inches high – so if your modular trays are not big enough to support this amount of growth then you will need to transfer them into pots where they can continue to grow, forming a healthy root ball, before they are ready for transplanting outdoors. When we describe sowing indoors this could be in a spare room, or a greenhouse, polytunnel, cold frame etc. |
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How To Transplant Your Broccoli
Once your young broccoli plants reach 4 to 6 inches in height they should be strong enough for transplanting outside – although it’s best to harden them off first so they get used to the outside temperatures.
When transplanting the broccoli – and this applies to any young plants when they are being transferred into the ground – try not to disturb their roots as this can put a check on their growth. Plant the young broccoli so that they are deeper into the soil than they were in their pots, ideally so their lowest leaves are at the surface of the soil. In this way you are encouraging them to root deeply and firmly – which is important for these brassicas which can grow tall so need as much firm anchorage as possible.
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When transplanting plants, if you want to make your life easier and planting more efficient, use a dibber. It lets you make uniform holes ready for the roots of your plants to fit into, so you can plant a full row of broccoli with minimum effort. This garden dibber is particularly good as it has an offset handle which helps to make it comfortable to use and control whilst its stainless steel head ensures longevity. |
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Although we always recommend checking the seed packet for spacing advice, remember, broccoli likes space to grow in. So you should be looking to space them between 24 to 30 inches apart.
By providing them with space you are giving room for good air circulation, which should reduce disease. It also gives them more space to grow – so you should get more side shoots and as a result bigger harvests.
When To Sow Broccoli Outdoors
Rather than sowing indoors, you can sow broccoli seeds directly into the ground where they will grow until they are ready to harvest. This does, however, prevent you from sowing early to get an early harvest, but it does mean that you don’t have to spend any time transplanting the young plants into the ground.
Again, always check your seed packet – the variety you have chosen will show the dates for when it can be sown – and the dates for sowing indoors or outdoors.
The easiest way to sow directly into the ground is to make a shallow drill about ¾inch deep in straight lines along your prepared ground. Then water along the base of the drill. You can now sow the seeds – space the seeds approx. 24 to 30 inches apart – sowing a few seeds at each point, with the aim of finishing off with one seedling growing at each point. This means if all the seeds germinate then you would thin them out, only leaving the strongest seedling in place to continue to grow.
Sowing directly into the ground does mean that once the seeds germinate the young seedlings will be faced with lots of potential pests which could eat then as soon as they appear – slugs or snails for example. So you are best to provide them with some form of protection – this could be by covering the sown area with garden fleece or insect proof netting or covering them with a cloche.
Looking After Your Growing Broccoli
Just like any brassica crop, there will be some tasks to carry out whilst growing broccoli which should help result in a bumper harvest.
Watering - make sure to water about once a fortnight and during dry spells - you don’t want them to run out of water as this can cause them to ‘bolt’. Equally, be careful not to over-water, as this can damage plants, especially the over wintering varieties of broccoli. Broccoli like moist soil, not soggy soil and consistency is key to a healthy crop. Ideally water first thing in the morning so your plants have time to soak up the water.
Feeding - once your broccoli plants have reached approx. 8 inches in height it’s time to start feeding them with a nitrogen-rich fertiliser. You should feed them again when they have grown to be 12 to 15 inches in height and then again when the buds start to form.
Weeding - weeding between your broccoli plants regularly is essential if you want to have bumper crops. Pulling up weeds or working the soil around the base of the plants with a hoe to kill the weeds whilst not damaging the plants are the easiest options.
Providing Support - with some varieties growing up to 3ft in height, if you have tall plants these should be given support, especially if they are in an area where they could be damaged by wind. You can also help to prevent the plants being pushed around and their roots loosened by piling up soil around the base of the plants.
Top Tip
‘Mulching’ is a great gardening term which will benefit many of your plants – including broccoli – by helping to retain soil moisture, suppress weeds, adds nutrients, and can help to insulate the plant roots. Basically, it involves covering the surface of the soil with a thick layer of organic matter – this could be garden compost, manure, or bark chippings. A little time spent doing this could help to save time on weeding, watering, feeding etc. and should result in better crops.
Protecting Your Broccoli Crop
Like any brassica crop, when you are growing broccoli it can be affected by a range of different pests and the most effective method for protection is to cover your crop with an insect proof netting such as enviromesh, or a garden fleece, like cosygrow. It’s best if you can support this covering with canes or a frame and anchor it to the ground to prevent pests from getting under the mesh.
Cabbage Root Fly – with the adult flies resembling house flies, it is their larvae which cause the problem to brassica plants. Up to 9mm in length these white maggots will tunnel their way into the roots of the plants, resulting in stunted growth or at their most destructive the plants will wilt and die.
Cabbage caterpillars – the caterpillars from a variety of butterflies and moths may decide to treat themselves to your broccoli plants. They will eat their way through leaves from the underside and eat their way into the heads from the bottom. For this reason they can be hard to spot, so you have to be on the look out for the butterflies or moths as they come to lay their eggs.
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Aphids – there are several species of aphids that you might find feeding on your broccoli plants, including turnip aphids (Lipaphis erysimi) or mealy cabbage aphids (Brevicoryne brassicae). They will feed on the underside of leaves or in the heads of broccoli. As they feed, sucking on sap, they will damage the plant and potentially infect the plant with a virus. The honeydew they produce as they feed is a sticky material which could attract ants and can become covered with a growth of sooty mould. With severe infestations the plants will be stunted in growth or wilt. |
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Club root – as the name suggests, this affects the roots of brassicas, including broccoli, leading to swollen, distorted roots which lack the finer roots you would normally see in a healthy root structure – the resulting roots could be described as ‘club’ shaped. This results in growth being stunted and in the worse case the plants will simply die.
Pigeons – common all year round they will damage many brassica crops, pecking at the leaves and ripping off pieces, leaving behind just the stems. If you have problems with pigeons on your allotment constructing a cage over the crops which they tend to destroy should help as you will be forming a physical barrier between the pigeons and the plants whilst still allowing you to access for care and harvesting.
Harvesting Broccoli
If you have not grown broccoli before, then you might not know when it’s time to harvest. If you want to harvest a large head of broccoli, then you need to cut it from the plant when it stops increasing in diameter and the buds are tightly packed and dark green – that’s the best time to harvest.
However, if the buds start to turn yellow then you need to harvest it straight away – this can happen in spells of hot weather, so you need to check regularly. As the buds turn yellow the broccoli will change in taste to become bitter.
Gardeners will sometimes describe this as ‘bolting’ when the plant starts to flower prematurely. Broccoli is a cool weather crop, so too much heat and fluctuations in temperature can cause it to bolt.
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Depending on the variety of broccoli you have grown you will not only be able to harvest the main head of the plant but also side shoots – once you have harvested the main head the side shoots will continue to mature until they are ready to harvest too. It can take the side shoots weeks after the main head has been harvested to be ripe enough to pick – so you could be picking from the same plant for a couple of months – the more shoots you harvest the more the plant should produce. |
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When harvesting broccoli this is best done using a sharp knife, as this won’t damage the main plant and will let you be precise with the cut – you should aim to leave two to three inches of the main stem on the plant.
Once you have harvested all the florets – top and side shoots – then the remaining plant can be added to your compost heap – don’t forget, if you cut up the plant into pieces these will compost faster.
Why Grow Broccoli?
Did you know that broccoli is classed as a ‘superfood’ and is one of the top foods when we think about healthy eating? Broccoli appears to offer so many benefits when added to your diet that it certainly should be something you start to grow yourself.
Low in calories – 34 per 100g
Rich in nutrients – to improve bone strength – these include vitamins C, & K, together with calcium, copper, zinc, magnesium and phosphorus.
Contains lutein and zeaxanthin – these pigments are linked to healthy brain function, nervous tissue function and protect against age-related cognitive decline.
Contains natural compounds linked to cancer prevention – classed as a cruciferous vegetable, the compounds it contains helps to neutralize carcinogens to help prevent cancer cells from growing and spreading.
Provides fibre – approx. 2.6g dietary fibre in 100g of broccoli – fibre supports your digestive health, helps lower cholesterol and blood sugar levels.
Very low in fat – broccoli only has 0.4g of fat per 100g when raw, only increasing to 0.6g when cooked.
High water content – approx. 89% water when raw – helping to keep you hydrated.
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Eating broccoli is a healthy option for most of us – however if you have a thyroid issue your doctor may advise you to only eat small amounts of broccoli as it may interfere with the adsorption of iodine. Broccoli can cause bloating and gas as it contains sugars that your small intestine and stomach have difficulty digesting. As the intestinal bacteria works on breaking down the sugars this causes bloating and discomfort. |
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Our growing guides are created from our personal knowledge, information gathered by speaking to other gardeners or manufacturers in the gardening industry, by reading gardening magazines and devouring information from books and the internet. We aim to be as accurate as we can, so if you find a mistake, please remember, we’re only human. if you have any queries you can contact us today!