Cauliflower and Kohlrabi

You need only a few cauliflower plants, therefore indoor propagation is totally worthwhile. Sow sparingly and resist the temptation to plant out too many of the same variety at one time, because you are then likely to have a glut. Cauliflowers from any one sowing will mature at a similar time.

• Seeds germinate quickly, but often unevenly – first leaves appear in four to six days.

Sowing conditions

As for cabbage, in temperatures as low as 10 °C /50 °F. However, you see better results when it’s 15 °C/60 °F or higher. Early sowings can be germinated on a windowsill.

Sowing time

See the table above.

Do check the seed packet suggestions, because each variety matures best at a different time of year, from sowing at a particular time. First sowings are from mid-February under cover, and last sowings can be October under cover. There is a mass of possibilities.

• For cauliflower harvests in autumn, the last sowing date in temperate climates is late June.
• Sowings in and after July need to be biennials, giving time for them to grow into medium-sized plants before winter, for eventual harvest in spring.

Sowing method

You want one plant per module, so either sow in a tray to prick out, or sow two seeds per module and thin to one. For hybrids’ expensive seed, I advise to sow in a tray, then prick out.

After a week or so, prick seedlings into modules of 3–5 cm/1.2–2 in width. They need full light, otherwise stems grow long and thin (‘leggy’). Early sowings can grow in an unheated greenhouse because seedlings tolerate some frost.

Pot on?

You have options. Either transplant at four weeks from sowing, or pot four-week-old seedlings into a 7 cm/3 in pot. From a very early sowing, potting on may gain an earlier harvest, plus it buys time if the planting bed still has a different vegetable, so is not ready yet for transplants.

Grow in a slug-free bed, with compost the only mulch. Set plants deep in the ground so that all or most of the stem is below surface level. Water in, and make sure the module or pot stays moist for the first week.

Transplant size

As for many brassicas, a plant height of 10–18 cm/4–9 in is good, according to conditions and when the ground is ready.

Transplant time

From mid-spring to late summer, according to the variety sown, and when.

Spacing

Space at 45–60 cm/18–24 in, depending on how large you want your plants to grow. This means that beds can easily be filled with only a few plants, not always a desirable thing if space is short.

You can reduce the need for space by making just the two sowings I recommend: (1) late winter to early spring, and (2) midsummer.

• Cauliflowers’ need for space is mitigated both by their speed of growth, and how they can overwinter. There is time after clearing plants from sowing (1) to grow a lot of other vegetables, and you can plant biennial cauliflowers from sowing (2) after significant early harvests.
• Each harvest requires less growing time and fits nicely with other sowings. A contrast is courgettes/zucchini, whose growth period is longer and spans both the main spring planting and summer planting times.

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How often

Once transplants are watered in, they can be left unwatered for much of the time unless it’s exceptionally dry. Once you notice the central leaves folding over an initiating curd, give water every two to three days if it’s dry.

At Homeacres, it’s rare that I water cauliflowers. The main time they need water is in late spring to early summer, if the weather is dry, as the first plantings grow large and then mature.

How much

Cauliflowers grow best in temperate climates with steady moisture. If your climate is dry, and perhaps hot as well, you may struggle to grow them unless you can provide a lot of water.

Extra mulch to retain moisture?

Worthwhile only in very dry climates.

How to judge readiness

When plants are large, check every few days for the first signs of a curd forming. Once you see a baby curd, hopefully with lots of healthy small leaves still wrapped tightly around it, you can expect a large cauliflower within about one week, depending on the level of warmth. In a cool spring, and for Romanescos in early winter, this could take a month.

How to pick

Use a sharp and solid knife to cut through the main stem, as well as a few leaves. The leaves are edible and tasty, as with broccoli leaves. It’s another advantage of growing your own, the bonus of more to eat from one planting.

When to pick and how often

Unlike broccoli, cauliflower curds are a single harvest, followed by no, or very little regrowth of any new curds. Romanesco sometimes makes secondary curds, but they are small and rarely worth waiting for in my experience. Secondary growths on widely spaced plants is not efficient, in terms of harvest weight per area.

• Summer cauliflowers can quickly open into seeding florets, with some decay and off colours, all within a few days of them having been a beautiful cauliflower. Don’t wait too long in summer before cutting your glittering prize.

Cauliflowers in autumn and spring will stand in good condition for longer, especially in spring when there are fewer insects to eat them. Likewise, when Romanesco are maturing in late autumn, or even early winter, they stand for up to a month because they are maturing so slowly.

Storing

At temperatures below 10 °C/50 °F, cauliflowers may store for up to a week. If they were very mature when you cut them, they are best eaten within two to three days, because some fungal decay and discolouring is probably already happening.

Saving seed

As for cabbage, I suggest leaving this to professionals, because of the space, time and expertise needed. See Real Seeds website for more information.

Which pests are likely, and when

As for cabbage, plants are susceptible to pigeons, rabbits and several insects. Most protection from insects is needed in summer months.

There is nothing worse than caterpillars in otherwise lovely cauliflowers, likely from midsummer and through autumn.

Protections needed

Use a cover of fleece for early plantings to give warmth, and cooler mesh for later plantings to protect from insects. If using mesh on spring plantings, use the finest grade in order to reduce damage from flea beetles, which are worse in that season compared to summer and autumn.

• Fleece can even sit directly on transplants, while mesh is usually heavier and is better supported by hoops when plants are small.
• The most damage from flea beetles is to the small leaves at the centre of plants, because some plants then struggle to even grow at all, after losing their growing tips.
• When flea beetles eat leaves through a mesh cover, the damage is not too significant, hence it can work to drape mesh on top of leaves.

Keep a cover on young plants, until you feel confident that insects and pigeons are not going to eat them. This may mean a cover until maturity!

For protection from caterpillars on uncovered plants, spray Bacillus thuringiensis every 20 days.

Other likely difficulties

Clubroot is possible but relatively rare. Spores are most active in warm soil, with less damage to overwintered cauliflower plants.

Clubroot results in galls or swellings, on roots and lower stems. These impede the uptake of nutrients and water.

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

• You may discover resistant varieties for sale – worth a try but no guarantee. Clapton F1 is sold as ‘clubroot resistant’.
• Clubroot thrives in slightly acid and wet soils, while no dig reduces the incidence. Worth spreading a little lime in spring every year to lessen the damage.

Non-heading of summer-sown cauliflowers, which you expected to head in the autumn but do not, suggest that in the following year you need to sow two to three weeks earlier.