Brassica oleracea var. Acephala
Kale is loose-leaf cabbage, in many shapes and colours. This reflects in the name ‘Acephala‘, which means without head, contrasting to the cabbage group ‘Capitata‘, with head.
Kale has been around since Roman times or before. Its ability to stand temperatures below even -10° C/14° F makes it a valuable winter staple. On the other hand, kale plants struggle in excessive summer heat. This reflects their coastal origins.
- Days from seed to first harvest: 50 for salad leaves, 70 for cooking
Kale seeds sownKale ready to harvestEarly springThrough summer, autumn, perhaps winterEarly summerLate summer to spring, depending on winterLate summerWinter to spring, best under cover
- Best climate is moist, temperate, cool rather than hot. It grows a little in mild winters and survives cold ones.
Why grow them
I bracket kale with chard, as a super-reliable vegetable banker, although with more pests. At almost any time in a long growing season, you can harvest a few leaves of kale. There are not many new ones in the winter, but each one is precious. Every winter harvest feels special.
Choose from the many different varieties in a seed catalogue, whose variations include all these possibilities:
- Leaves good for salad or cooking
- Leaf colour from green to crimson
- Texture from smooth to curly
- Either productive green or less productive ornamental
- Harvests from tall plants, or short ones
- Spring harvests of small shoots with flower buds, similar to broccoli
Homegrown kale has stronger flavours than bought kale and excellent nutrition. Vitamins C and K, for example, are at a maximum in fresh leaves, which also boast 3% protein.
Eat raw and cooked
You can prepare kale in so many ways.
- If you like it raw, grow tender flat-leaved varieties such as Red Russian and the Ethiopian types, also Sutherland from Scotland.
- Roasted kale tastes exotic, partly depending on how much oil you add – a high amount results in kale crisps.
Most kale leaves have a fibrous stalk up their middle. Simply cut off the two tender sides and discard the stalk for compost.
Pattern of growth
You can grow kale as an annual plant, sown in spring and removed in the autumn. It is in fact biennial and flowers in the second spring, as long as it survives winter. The flowering shoots are super tasty, like mini broccoli.
There are a few varieties of perennial kale. This term causes confusion when sometimes misapplied to varieties that are slow to flower and behave with a perennial tendency. See the photo of Oisin Kenny in Galway, Ireland – the last photo at the end of the lesson.
True perennial kale does not flower and therefore makes no seeds. As a result, it is propagated from stem cuttings, an easy process that takes only a few weeks.
If you don’t have stems, you may be able to buy a rooted plant, grown from a stem.
Suitable for containers/shade?
Kale tolerates shade, though best to plant in the sun.
For growing in containers, select a dwarf variety. Dwarf curly kale, for example, is nicely compact and its small size means that it won’t be diminished by a restricted root volume.
Kale’s rapid rate of growth and continual harvests do come at a price. They have a great need for moisture and, after the initial flush of growth, you need to feed plants in containers (though not in beds).
Cavolo Nero, or Black Cabbage and Tuscan kale, grow dark green, long leaves, on plants of varied height according to the seed supplier. The leaf texture is savoyed.
Kalettes are half kale and half Brussels sprouts, a modern hybrid. Tall and vigorous plants grow large harvests in the dead of winter. They are super tasty – pigeons love them too!
Taunton Deane kale plants, rooted and ready to be transplanted, with broad-leaved sorrel at the back
Lerchenzungen (‘Lark’s tongue‘) is perhaps the German equivalent of Tuscan kale with long leaves, except that they are curly and lighter green. An equivalent variety with broader leaves is Westlandse.
Hungry Gap grows its green, mostly flat leaves for longer in spring, before flowering quite late in spring.
Ethiopian kales are flat-leaved and tender, good in salad. Also, they flower in the first year so the harvest period is short, in a temperate climate at least.
Dwarf Curly and Dwarf Red Curly grow as named, into bushy plants with leaves better cooked than raw.
Sutherland is a tall, green flat-leaved kale with tender leaves.
Red Russian (‘Ragged Jack’) has lovely pink tinges to its green, serrated leaves. They are tender raw, and the flower shoots in spring are especially prolific and tasty.
Red Devil has lovely red stalks in smooth and tender leaves, on small plants.
Thousand Head does indeed make several stems from one plant – not so good if you want large leaves. However, in spring it’s excellent, with many tender shoots from one plant.
Redbor and Darkbor are dark red, tall hybrids.
Scarlet kale is not a hybrid, less tall and a little less crimson.
Recently, breeding has worked to create gorgeous colours. Candy Floss and Emerald Ice look amazing and taste good.
Taunton Deane is a tall perennial kale, possibly discovered in Somerset. Plants can continue to grow for more than a decade. It has now been nine years since I rooted the small stem of my oldest plant – the photo below shows you its reclining, stable posture.
Daubentons is a French perennial, mostly under 1 m/3.3 ft high and with many stems, plus smaller and slightly more tender leaves than Taunton.
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 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.
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.
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.
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.
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.
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.
Kale makes a great interplant any time in summer. Wherever you have vegetables soon to finish, with some light between their leaves.
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.
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.
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
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.
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.
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.
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.
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.
Clearing usually happens in spring. Before that, you can enjoy the tender flowering shoots, equivalent to small broccoli, until in time they become thinner and more fibrous.
The thick main stems are best twisted round and round, until most roots have snapped off and remain in the soil. Or use a sharp spade to cut around the base of stems.
Prepare and plant
For all winter brassicas, I recommend adding compost for the year ahead during winter, while they are still growing, and up to six months before final clearing. Here are the advantages:
- It’s easy with kale because the cropping leaves are well above soil level and plants are widely spaced.
- Soil organisms are nourished through winter and protected from extremes of weather.
- Spread 2.5 cm/1 in of compost any time from mid-autumn. If it happens to be lumpier than usual, that is fine, because weather softens lumps before spring.
- In spring, the turnaround time is quick, between clearing kale and starting another vegetable.
There is little ground preparation, except to walk on the beds if you had to lift soil when removing each plant.
Kale’s finishing time in spring means you can follow with any other vegetable – perhaps not a brassica, although it’s possible.