Broccoli

Seeds appear in three to seven days, depending on warmth. They are definitely worth raising under cover because of all the possible insects that eat brassica seedlings. Also, you may well be growing hybrid varieties, whose seed is expensive. Plus if you lose a sowing, you have lost critical time which can’t be replaced, as well as valuable seeds.

Propagation/sowing conditions

Germination happens in a wide range of temperatures, say 10–32 °C /50–90 °F, and is particularly strong in summer months. This follows from the lifecycle of brassica plants: they flower in spring and drop seeds in early summer, then grow again.

Sowing time

Mid-February, or late winter, is the time to sow under cover, in warmth. Make sure that your variety description is for cropping in early summer, not autumn.  The earliest sowings have a chance to grow and crop before butterflies arrive.

• Broccoli to crop in autumn does well from sowing in early summer, as do varieties for cropping in the following spring.
• The best two times to sow kaibroc are late winter and midsummer. Try a few dates to find the best ones for your climate.
• Other sowing times are possible, but the ones I give are for strongest growth, with relatively less insect damage.

Sowing method

With the aim of having only vigorous plants, rather than a random mix of stronger and weaker ones, it’s worth sowing in a small tray, from which you can prick out the strongest seedlings into modules, one per module.

• Seedlings are easiest to prick at four to five days old, when you see only the cotyledon leaves.
• Please ignore the common advice to prick out after you see a first true leaf, which actually makes it difficult because seedlings already have a lot of root. It takes longer and results in more root disturbance.
• Or sow two seeds per module and thin to the strongest. However, this means you need more seeds and lose the chance to bury stems when pricking out, so seedlings will be more leggy.

In a 2.5 cm/1 in module, plants could be ready within two weeks from pricking out, and in a 4 cm/1.5 in module you have about another week before transplanting. There is leeway with brassicas because they tolerate an amazing amount of neglect, such as running out of nutrients in compost before being transplanted, after which they always recover.

Nonetheless, best growth is from minimum interruption, as far as possible. Transplant as soon as they are ready, before you see yellowing of the cotyledon leaves.

Pot on?

Not usually necessary, except for summer sowings if you are waiting for a preceding vegetable to finish. Interplanting the broccoli between a soon-to-finish vegetable, say onions, may be an option instead of potting on.

Transplant size

Any height from 10–15 cm/4–6 in is good, and it’s easier plus quicker to transplant brassicas at the smaller end of that range. Set plants deep enough for most of their long stem to be below surface level. It’s fine to bury the cotyledon leaves if they are still there.

Transplant time

Broccoli plants are hardy, so your first sowings of late winter can go out in late March, without hardening off. Cover with fleece which can lie directly on the plants, to hold warmth close. This also serves to keep off pigeons and cabbage root flies.

Plants in summer will encounter many pests, and they are best covered against insects. We use mesh supported on hoops.

Spacing

There is a range of spacings, according to the types of broccoli. Also, wider spacing is for longer-lived plants and larger heads. With calabrese, for example, you can plant at 40 cm/16 in, for fewer plants with a substantial first head and four to eight weeks of side shoots, compared to 30 cm/12 in for more plants with medium heads and three to four weeks of side shoots.

• Calabrese: 30–40 cm/12–16 in
• Kaibroc: 30 cm/12 in
• Sprouting broccoli: 45–50 cm/18–20 in

The wide spacing of sprouting broccoli invites some interplanting. I have tried this with beetroot for salad leaves, even for small beetroot. We had best results with interplants of dill, coriander and parsley, some of which survived through winter. Lettuce and endive could work too.

Support

The small seedlings we transplant grow uniformly at first. Then, at about six weeks since being planted, they are suddenly quite tall.

Sometimes after a storm they lean on the ground and look distressed. Fortunately, the growing point and new stem are soon upwards again, and you would hardly know there had been an issue.

However, you will have lost some space because when they lean or recline they are in the pathway. I find it simplest to put up with this and brush past, but you could use a stake and string, or string supports, such as those I show for broad beans.

How often

Give water every day or two, for the first week after transplanting; thereafter not much unless exceptionally dry. Main watering is as harvest approaches. Also, in very dry weather, summer planted broccoli will benefit from a good dose of water twice a week, for the first two weeks.

Of the most benefit is giving water to summer broccoli when close to harvest, once you see small heads initiating. If it’s hot and dry at that point, water every two days to keep plants growing strongly, with bigger broccoli heads.

How much

Brassicas are tolerant of dry conditions, but if you look closely you may notice the leaves are matt rather than shiny, and the colour is slightly more blue rather than bright green. This is not critical, as long plants have an established root system, and are not close to point of harvest. Just a small amount of water can suffice to keep them alive. Then, once harvest time approaches, give a lot of water.

Extra mulch to retain moisture?

This is good in dry climates, and the wide spacings of broccoli allow easy distribution of mulch materials.

It’s highly worthwhile to remove, regularly, any lower leaves you see, once they start to lose their full colour and turn a little pale or yellow. Also remove leaves that are suffering noticeably from pest damage, which again is normally the older leaves closest to the ground.

Detach leaves from the stems by a downward push on the leaf stalk close to the main stem. This ensures a clean break with no decaying stalk left behind.

The result is:

• Good airflow around all leaves at the bottom.
• Reduced Alternaria disease, thanks to leaves being drier.
• Fewer slugs, because there is less for them to eat, and no decaying leaves for them to hide under at ground level.

‍

How to judge readiness

Broccoli is an assembly of hundreds and thousands of small flower buds. Initially, the buds are tiny and tightly clustered together. Then, in warm weather, they quickly swell and elongate, with buds soon opening to small yellow petals. If this happens, the stem will turn woody and fibrous quite quickly. Plus there may be some decay and yellowing inside the main head.

• The largest and most tender harvests are in the middle stage, between tiny buds and flower petals opening. When the temperatures are above 21 °C /70 °F, this gives only a short period of perfect harvest.
• If you have many plants and the weather is warm, you can’t eat them all in the short period of perfect development. It’s worth taking some early harvests of slightly immature heads, followed by larger harvests of mature heads.

If possible, as harvest approaches, check your plants every day right at the centre to find the first little broccoli heads, usually when you see new baby leaves curling inwards. At that exciting time, they are clustering over a developing head, as with cauliflowers.

How to pick

The stem of a main head is usually fat and strong, and best cut with a knife in order not to damage the plant. Cut at whatever height you choose, to eat more or less of the stem. Best eating quality will be when the knife slides through easily, meaning there are few woody fibres.

Side shoots are quite different and often easier to snap off. They snap most easily right where they branch off the main stem, but with the lowest part of each stem perhaps being fibrous.

You can also cut or snap them halfway, just above where you see smaller side shoots coming out of that side shoot’s stem. That gives a longer period of harvest, with ever more side shoots of smaller size.

When and how often

1. Sowings of early spring give a first harvest in early summer, and continue producing side shoots for a month or so, every few days. Probably but not necessarily, it’s worthwhile to remove plants after the first flush of side shoots, for two reasons:

• Harvests are decreasing.
• There is more time for succession plantings to grow large.

2. Summer sowings for autumn harvest will crop either throughout autumn, depending on the variety, or through late winter and spring. In cool weather, there is less rush to harvest as soon as you see broccoli ready; in winter months, you can pick your moment for harvesting.

Storing

Best temperatures for keeping broccoli for more than a day or two are below 10°C/50°F. In summer warmth, best keep them in the fridge, because harvested heads turn yellow within two days and decay quickly.

Saving seed

This requires a lot of time and space, partly from requiring several large plants. See specialist manuals for how you would manage the process.

‍

Which pests are likely

• Flea beetles do the most damage to seedlings and are prolific in the spring and summer.
• Cabbage root flies can kill plants by eating their roots, usually in late spring.
• Rabbits eat the tender leaves of any plant and are partial to brassica seedlings, which can disappear overnight as a result, leaving only a stem.
• Caterpillars arrive by mid-summer and are problematic for about three months after that.
• Pigeons can eat so much new leaf that they risk killing plants at any time of year, depending on where you are.

Protections needed

Because of pests being so likely, especially on seedlings, I recommend you have some covers ready.

• Use fleece in the spring, because that adds warmth at the same time as protecting from whatever pests are around.
• Summer plantings need covering with mesh.
• After removing mesh from large plants, you could spray them every 18–20 days with Bacillus thuringiensis to protect against caterpillars.
• In winter, when insects are hardly a problem, bird netting will probably be necessary because of pigeons.

Other likely difficulties, including disease

Club root is the main disease problem, but it’s relatively rare. Spores are most active in warm soil, with less damage to winter brassicas such as spring cabbage, whose growth is mostly in the winter months.

The result of club root infection is formation of galls or swellings, on roots and lower stems. These impede the uptake of nutrients and water.

It is spread in many ways: by the import of infected plants, from infected neighbouring plants, by use of infected tools, by moving infected soil and even from surface water runoff. Spores remain dormant for several years, until coming to life again on host plants.

• There are some resistant varieties. However, this is resistance, not immunity, and growth is still somewhat diminished. There is more information on the Simply Seed website.
• Club root thrives in slightly acid and wet soils. As with allium white rot, no dig reduces incidence. Also spread just a dusting of lime in spring every year, to lessen the damage.

Alternaria leaf spot (Alternaria brassicae)

This can affect broccoli in the autumn. It occurs mainly after periods of rain, with temperatures around or above about 18° C/64 °F.

You see it as dark circular spots which increase in size, sometimes with concentric rings inside, and a yellow halo outside. It is common on older leaves, especially in less fertile soil.

• Regular twisting or breaking off of older broccoli leaves, and removing to the compost heap, is your best control. Use gentle downward pressure on each leaf, even if still mostly green.

‍