Kale

As with all brassica vegetables, raising plants under cover is highly worthwhile, for the reliability of plantings and minimum damage from insects.

• Seeds germinate in three to five days, even two in hot weather.

Sowing time

Sowing commences in March/early spring and continues to be possible at any time through the following six months. Choose a sowing time according to the size of the leaves you desire and when you want them, as I now explain.

• Sowings before mid-spring give kale throughout summer, generally for cooking because leaves grow larger and are less tender in heat. Harvests are abundant in summer then reduce through autumn. You can have a few new leaves until the following spring, in milder winters.
• Sowings in late spring to early summer give abundant leaves from late summer, through autumn less and less, and then probably until spring.
• Late summer sowing gives smaller plants at closer spacing – good for salad leaves in the winter months. They are especially worth growing under cover, unless your climate is warm.
• In Zone 10 climates, such as Florida and parts of India, kale’s best harvest season is winter, because it likes the temperatures and there are hopefully fewer insects.

Sowing method

As for all brassicas, sow in a tray to prick out seedlings or sow two seeds per module.

Usually you grow one plant per cell, but multisowing is an option for salad kale, even three or four plants in each clump.

Pot on?

This is worthwhile if you are waiting for ground to come ready.

Here we transplant kale every year in mid-June, after spinach. Best kale harvest is from sowing in early May and, 25 days after sowing, the plants are running out of space and food in their modules.

We pot them into 7 cm/3 in pots. This delays planting for up to two weeks while, say, the broad beans or spinach finish cropping. After clearing them, we transplant the larger kale plants.

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Transplant size and time

Kale plants are toughies. Even if you leave them too long in modules or pots, such that their leaves turn pink and purple from lack of nitrogen, they go ‘dormant’ and cease growing for a while until transplanted. Leaves then change back to a healthy green.

• Usually you transplant three to four weeks after sowing.

Transplant method

Make a deeper hole than the rootball.

• When transplanting modules, wiggle the dibber in each hole for more width and, above all, for depth.
• Or use a trowel for kale in pots.

Bury stems to give plants stability in wind. Push in firmly, always, then give water. The upper surface of each rootball can be 5–7 cm /2–3in below surface level.

Spacing

Space plants according to the size of leaves you desire, from 22 cm/9 in for salad kale, up to 45 cm/18 in for large leaves. A spacing halfway between gives many medium-sized leaves and several months of harvest.

Perennial kale can be 60 cm/24 in apart, but this is relevant only for market gardens. For home consumption, one plant should suffice. It needs space to root and to recline in time. My old one has dianthus (Sweet William) growing around its roots, with gorgeous flowers every year in early summer.

Interplant

Kale makes a great interplant any time in summer. Wherever you have vegetables soon to finish, with some light between their leaves.

Support

Most kales are strong-stemmed, not too tall, and support themselves nicely. However, if your site is windy and plants show signs of falling, one stake for each in late summer could be worthwhile, tied with stout string.

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You are transplanting mostly in summer, so give plenty of water at that stage and for a week after if the weather is dry. Beyond that, it’s a balance of weather and how much new growth you want.

• Kale puts up well with dry conditions, it just grows fewer new leaves and they are tougher!
• Then, with new rain in late summer, growth suddenly takes off again. Also, leaves are more tender and glossy, often really beautiful.

Extra mulch to retain moisture?

In my temperate climate, I never do this. But in drier climates, it’s worthwhile and feasible. Spread straw in the quite wide spaces between each plant, as soon as they are in the ground. Or even before that, if slugs are not a potential problem.

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How to judge readiness

One sign is that leaves of neighbouring plants now touch each other. During the preceding week or two, plants will have increased a lot in size.

• Look at leaf lustre and vigour, more than plant size and height – the latter is different for each variety.
• Don’t wait for plants of a dwarf kale variety to grow large!

How to pick

Work from the bottom, close to ground level for the first pick. First, discard the lowest, yellow leaves to compost.

Next, put your thumbs on the leaf stalk of the now lowest leaf. Push downwards to snap off the stalk, where it meets the main stem.

• You may not want to eat the stalk, but removing it keeps plants tidy and nice-looking, plus makes it easier to pick next time.

Keep picking higher leaves, until they are noticeably small near the top. Leave these to grow for perhaps a week in summer. Your harvest may be any number, from one to six lower leaves from one plant.

Still harvesting, ten months since sowing

When to pick and how often

• Pickings in summer and early autumn can be abundant, such that every second day you might pick one leaf per plant. Then, as autumn progresses, leaf size becomes smaller.
• Suddenly, by late autumn, plants that had been producing abundantly are now giving only meagre harvests.
• Pick fewer leaves to leave more on the plant, which helps photosynthesis to make new growth.

Harvest examples of kale, sown on 9th May and transplanted on 15th June on the no dig bed of my trial. Five plants at 30 cm/12 in spacing across a 1.5 m/5 ft bed, four of Black Magic and one of Scarlet. The preceding harvest in early June was carrots from a March sowing.

Date Leaves picked (kg)8th August0.9413th August0.2720th August0.7227th August 0.823rd September1.3610th September0.5217th September0.4824th September0.691st October1.088th October0.3915th October0.4529th October0.5019th November0.568th December1.33TOTAL  10.11 kg/22 lb from five plants, over five months = 2 kg/4.4 lb per plant

Storing

Kale turns yellow after picking unless kept cool, below, say, 10 °C/50 °F or less. Best to pick fresh in summer and perhaps weekly in winter, when growth is slow anyway.

Saving seed

As with broccoli (Lesson 5, Course 3A), this requires a lot of time and space, and is preferably the only brassica seed saving of that spring and early summer. See specialist manuals for how you would manage the process.

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Kale suffers the full range of brassica pests and diseases.

Which pests are likely

• Flea beetles do most damage to seedlings in the spring. They eat older leaves less, so kale in its second spring is not too damaged.
• Cabbage root flies can kill plants by eating their roots, usually in late spring, so not a huge problem for kale when transplanted late spring onwards.
• 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 midsummer and are problematic for about three months after that.
• Pigeons can eat so much new leaf that they may kill plants at any time of year. Their frequency depends on where you are – you will discover the local pattern of damage. Here they are not bad except in winter.

Protections needed

Because of pests being so likely, especially on seedlings, I recommend having a mesh cover ready. You will not need fleece, because we are not trying to grow super early kale from transplanting in early spring.

• Summer plantings in particular need a cover, say of mesh, preferably held up by hoops when plants are small. Otherwise, insects lay eggs on the leaves, where the mesh is lying on and in contact with them.
• After removing mesh from large plants, you could either spray every 18–20 days with Bacillus thuringiensis against caterpillars, or squash them when seen.
• In winter, when insects are less of a problem, bird netting will probably be necessary against pigeons.

Disease

Clubroot is the main disease but fortunately, it’s relatively rare, and spores are most active in warm soil so less damage happens to winter brassicas.

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

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

So how come the disease is not common?

• As with allium white rot, no dig reduces incidence.
• Many allotment soils have been abused by excessive cultivation, hence the widespread incidence.
• Clubroot thrives in slightly acid and wet soils. Spread a little lime in spring every year, to lessen damage.
• There are some resistant varieties – see this webpage. However, resistance is not immunity and growth is still diminished.

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