The supermarkets have helped to confuse the issue of what is broccoli and what a calabrese by calling both by either name. The large green heads you see in the photo (and generally referred to as broccoli) is Calabrese whereas the much smaller heads which can be green, purple or white are broccoli.
The flavour of calabrese is milder and much preferred by many to sprouting broccoli and it is an easier crop to grow.
A video companion piece to this How To Grow Calabrese article is available at the bottom of this page.
Calabrese require an open unshaded site with free draining but moisture retentive soil with plenty of organic matter. Nitrogen requirements are high so an addition of farmyard manure the previous Autumn is ideal. Sow from late march to early June. For a continual crop of tasty heads sow a few plants in late March, early May and again in early June.
Like most brassicas Calabrese is best sown in a modular seedling tray as the plants don't like root disturbance. Fill the seed tray with compost and brush off any excess. When filling the tray rub the compost through your hands to break up any lumps. Give the tray a sharp bang on your table to settle compost. With your fingers make small depressions in each cell about a fingernail or 1.5cm deep. Sow 1 or 2 seeds per module. If 2 seeds germinate you will have to remove the weaker seedling. Cover the seeds with another layer of compost then scrape across the top of the tray with a stick to remove excess. Gently water your seeds. A good tip is to use a plastic bottle with small holes punched in the cap. This is less likely to wash the seed around than the heavy spray from a watering can. Place your trays in your greenhouse, polytunnel, cold frame or windowsill to germinate. They should be ready to plant out in about 4 weeks.
When growing seedlings indoors be careful that they don't get leggy, i.e. long spindly plants. Seedlings become 'leggy' when they get too much heat and not enough light. If you are starting them off on a windowsill make sure they get as much daylight as possible. You can make a makeshift light box by placing a sheet of reflective tinfoil on the room side of the seedlng tray. This will reflect daylight onto the darker side of the plant. If the plants are on a heat bench or in a propogator and they are looking spindly, turn the heat down and try to give them as much light as possible.
If 2 brocolli seedlings have germinated in any of your modules you need to remove the weaker one. Don't pull the seedling out as you'll damage the roots of the one you want to keep. Nip the unlucky one with your finger nail or cut with a scissors.
It's important to keep yoru seedlings properly watered before you plant them out in the gartden. You are actually far better to under rather than overwater your plants. This may sound odd but making the roots search for water helps to develop a better root system. It's a bit like keeping fit. You do need to be careful, however, not to let the compost plug completely dry out or it will form a crust on top and won't absorb the moisture the next time you water. It will all depend on the weather of course but on a hot day you will need to water twice a day, if it's it's dull every 2 days will be fine.
Plants that have been raised indoors will need to get used to the outdoor temperature and conditions before they can be planted outside, this will take about a week to 10 days depending on the weather. The best way is to use a cloche or mini greenhouse. You can leave the cloche off the plants on dry frost free days and replace at night. Gradually increase the time with the cloche removed until the end of the week when you leave it off day and night. If the weather is mild you may not need the cloche, just move the plants outside for longer periods each day. If you have started your seeds on a windowsill you will need to leave them in an unheated room for a day or two before moving outside to the cloche.
Spacing determines the size of the head produced. Wide spacing of 45cm in rows 60cm apart will produce very large heads to impress your neighbours while the more common spacing for medium sized heads is 40cm between plants in rows 40cm apart.To plant your seedling make a hole in the soil the approximate size of the seedling 'plug'. You need to push the soil inaround the roots firmly with your fingers to get good contact with the soil. Dont firm down on the top of the soil as this can compact it and prevent moisture getting down to the plants roots.
Seedling plants can be planted up the the base of the first set of true leaves if the stem has got a little leggy from lack of light at the seedling stage. The true leaves are the second set of leaves produced after the initial rounded seed leaves. Water the plants after planting but do not soak them. You are better to transplant on a dull day or in the evening to prevent the plants wilting on a hot, dry day. A light sprinkle of seaweed/poultry manure around the planting hole will help your calabrese get off to a good start.
Calabrese can suffer from all the usual brassica diseases, you can view more information in our 'dealing with brassica pests and diseaes' article here. The most likely issues you may encounter are as follows:
Look out for blue tinged leaves which wilt in sunny weather. Recent transplants are most vulnerable and will die, when plants are lifted you will find small white maggots around the roots. Use cabbage collars fixed around the plant stems or cover the crop with protective mesh or fleece.
Cabbage caterpillars are active between may and October and lay clusters of yellow eggs under the leaves. When the eggs hatch the caterpillars will start tucking into your plants so it's easier to check the underside of the leaves periodically (or if you see white butterflies hovering around plants) and brush of eggs. To prevent butterflies laying eggs protect the plants a fine insect mesh.
Stems are severed at ground level resulting in the death of seedling plants. Leatherjackets and Cutworms are a similar grey/brown colour and live below the surface of the soil where the emerge from at night. If you find one severed stem search the soil in the vicinity and you are likely to find the culprit. To control use a nematode based natural insecticide.
With most varieties of calabresee you get two crops from a single plant. Initially a central dome will form, after this is harvested the plant will produce numerous smaller side shoots. The main problem with harvesting calabrese is the premature flowering. Check the plants at least twice a week coming up to harvest as the tight green buds will quickly open into yellow flowers rendering the plant useless.
Calabrese is best steamed rather than boiled as it will retain its flavour and texture better. Small spears can also be stir-fried. The thicker stalks are great for making soups like Broccoli & Stilton Soup.
There have been a number of studies that suggest broccoli can help protect you from cancer. Broccoli contains a chemical called sulphoraphane which helps neutralise cancer-causing substances found in the gut and can help against colon cancer - one of the biggest cancer killers in the UK
Broccoli also contains a compound called I3C that helps boost production of BRCA proteins. These are helpful against some forms of cancer including breast, ovarian and prostrate cancers.
How to Grow Calabrese Broccoli Video
Our You tube channel has nearly 4 million views! Watch our Calabrese Broccoli video with Andrew Davidson and professional organic grower Klaus Laitenberger. All our videos are filmed over a full season so you can see the sowing, planting, crop care and harvesting stages.
You can view our Sprouting Broccoli video by clicking the link or the Youtube icon.