how to plant, grow & care for kale
complete growing guide
Kale has become increasingly popular over the last few years, for its health-giving vitamins and antioxidants as well as its versatility in the kitchen when there is not much else growing in the garden. Being an attractive cut and come again vegetable it fits right into an ornamental border or even a window box, so that you never have to go very far for a few leaves for a salad or stir fry.
The secret to growing kale is to choose interesting varieties and unusual colours. You can grow the fashionable and elegant, black Tuscan kale, ‘Nero di Toscana’, but I prefer the less well known, ‘Red Russian’. It has a tenderer texture, producing an endless supply of cut-and-come-again leaves for five or six months at a stretch.
This growing guide will show you how to grow your own kale and how to avoid the common problems that can affect the brassica family.
- Common name: Kale
- Latin name: Brassica oleracea (Acephala Group)
- Type: Hardy biennial vegetable
- Height & Spread: 30-100cm x 60cm, but depends on variety
- TLC rating: Easy
- Aspect: Sunny open aspect
- Spacing: 30-60cm
- Yield: Up to 3kg per plant over 8 months of cropping
- Suitable for pots: Yes
- Grow in a greenhouse? No
how to grow kale
where to grow kale
Soil type: Kale is happy in most soils but prefers a moist, fertile and slightly alkaline soil.
Aspect & position: Full sun is best, but it will tolerate some shade. Shelter from strong winds is important, as it does have a tendency to blow over.
when to plant kale
You can sow kale seeds indoors in February and March and then outside right through to August to ensure a good supply through the summer, autumn, winter and early spring. Plant out seedlings from April onwards, once they have reached about 25cm in height.
how to plant kale
growing kale from seed
I sow seeds in April for early winter and then again in June for a crop that lasts until the next spring. I start the seeds off in 10cm pots of multipurpose compost and plant out when the seedlings reach about 25cm in height. Kale suits being sown into modules in this way as brassicas hate root disturbance. It’s just two seeds into each miniature pot. If both germinate, remove one, leaving the other to grow on with lots of its own space.
Growing brassicas from seed in June can seem a strange thing to do, but sowing a few choice brassicas in early summer means you can have delicious and interesting meals through those cold winter months.
If you have ordered our seedling kale plants, or your own seedlings are ready to go out, make sure you expose them to the elements gradually. This is known as “hardening off”, and is valuable even for the hardiest plants if they have been cossetted in a warm place. Let them adjust to outdoor temperatures for a few days, bringing them in at night until they are ready for the great outdoors.
planting kale seedlings
Once your seedlings are about 25cm tall, plant them out into their growing position. Plant seedlings about 50cm apart (90cm for the larger varieties), as they can grow upwards of a metre tall.
I put them in with a good mulch of well-rotted manure or mushroom compost - these plants love it rich. Firm soil is also essential for good brassicas. They are tall plants which shallow roots, so they need a compact soil to help them stand upright. Bash the soil down with the back of a spade and walk around again and again. After you’ve got your plants in, do the same again, trampling the ground around their roots with your feet.
To avoid clubroot disease avoid planting brassicas in the same ground for three years.
how to care for kale
Kale plants don’t require huge amounts of water and are generally untroubled by pests, compared to some of the others in the Brassica family. Water in your freshly transplanted kale seedlings, but after that they will only need a drink if there is a prolonged drought.
Harvest when the leaves reach 15cm long. Being a cut-and-come-again variety, the leaves you take home will quickly be replaced by more, making this a great value for money crop. You can also start harvesting kale at the micro-leaves stage, pick the leaves small and use them in a winter salad.
One good tip is to try and harvest evenly, rather than one plant at a time, to avoid exhausting individual plants. It is best to cut or snap the leaf stalks quite close to the stem, but only take about four leaves off per plant, so that each plant has enough leaves left to recover and produce more.
Store your kale in the fridge for up to 10 days or blanch and keep in the freezer for up to 6 months.
- Sow seed indoors in February or March, outdoors in April onwards.
- Plant out seedlings from April onwards.
- Continue harvesting last year’s crop.
- Start harvesting young leaves for salads in May or June.
- Continue regular sowings throughout the summer.
- Watch out for the arrival of cabbage white caterpillars.
- Harvest leaves regularly, a few from each plant.
- Continue harvesting – the frosts bring out the sugars in the plant making the leaves sweeter still.
pests, diseases & common issues
Unfortunately, pigeons are brassica connoisseurs, so if they have found your patch you might need to protect your young kale seedlings with netting. Luckily, they seem to lose interest once the plants mature, so with luck you can remove the netting once you want to start picking the crop yourself.
cabbage root fly
Cabbage root fly can be very damaging to young transplants as they eat away at the roots and weaken the plants. The first generation usually emerge in April, just as you are planting out. If you practice crop rotation you will break the cycle of last year’s pupae hatching out into the next crop.
You can also deter the adult flies from laying their eggs close to the root by placing a brassica collar or circle of carpet underlay around the stem. Enviromesh or horticultural fleece will also prevent the adults getting anywhere near your plants.
cabbage white caterpillars
Cabbage white caterpillars arrive a little later in the season, in June or July, with the white butterflies laying their bright yellow eggs on the underside of the leaves, and the stripey green caterpillars emerging soon afterwards, ready to strip whole plants to a skeleton if you are not sufficiently vigilant.
Rubbing out the eggs as soon as they are laid is the least gory solution. Once they have hatched into hungry caterpillars the squashing is messier, but essential if you are going to get a decent crop.
The good news is that kale will recover from an attack, giving you a later crop in the winter once it is too cold for the caterpillars. Netting, Enviromesh or horticultural fleece will in theory keep the butterflies out, but they are remarkably devious, finding the slightest chink in your armour. If they can’t physically squeeze in they will actually lay their eggs through the netting if it’s touching the leaves. Of course, the netting keeps you out too, so you can neither squash the eggs nor pick the crop, so unless you make a walk-in brassica cage, you will probably be frustrated.
Adult whiteflies are active throughout the year, overwintering on your kale and if you are unlucky, flying up in clouds as you pick the leaves. A mild infestation will not harm the plant, and they are easily washed off in salty water once you get them home. But a really bad attack will damage the plant and lead to sooty moulds appearing on the leaves. Spraying with an insecticidal soft soap or SB Plant Invigorator might be your only option.
mealy cabbage aphid
These aphids hide under the leaves in dense greyish-white colonies. Scrape them off if you see them appear, and then rely on their natural predators ladybirds, hoverflies and lacewings to come to your aid and finish the job.
This is an insidious soil borne fungal disease that does exactly what you might expect – it turns the roots into a contorted useless stump, and causes the plant to wilt and eventually die. It is important to buy only plants from a reliable source, or raise your own from seed grown in fresh bought-in compost. Once it is in the soil it is very hard to eradicate, although liming prior to planting out will help, and a strict rotation is paramount.
why is my kale not growing?
This could well be caused by the aforementioned clubroot or cabbage root fly. Pull up the worst looking plant and see if you can see anything amiss below ground. There could still be time to start again with some new seed in fresh ground.
why is my kale plant turning yellow?
There are bacterial infections that can cause yellowing of kale leaves, also the mealy cabbage aphid (see above) can create yellow spots, but the most likely cause is stress. If you have left seedlings in their small pots for too long, they will have run out of food, so planting them in the open ground will definitely help. If you are growing them on to adulthood in a container they also might be struggling for enough water and nutrients. My favourite pick-me-up for hungry looking plants is a foliar spray of seaweed, you will soon see a huge improvement.
what's eating my kale plants?
The most likely culprit is the cabbage white caterpillar or pigeons both of which can soon strip the leaves to a depressing skeleton. If you are seeing little pin holes in the leaves, this is more likely to be a flea beetle attack. These shiny black beetles jump up from the soil surface when the warm weather comes and will attack your seedlings. Keeping the soil moist will help deter them until the plants are big enough to fight the battle.
why is my kale plant wilting?
This will either be caused by drought, overwatering or root damage. Once you have ruled out the first two (by watering or withholding water), pull up the worst affected plant and inspect for either clubroot or cabbage root fly.
why are my kale seedlings leggy?
Most plants get leggy (elongated or etiolated being the more technical term) if they are struggling for enough light. Make sure you haven’t sown the seed too thickly in the pot or seed tray. Just a pinch of the tiny seeds, sprinkled about 2cm apart will be plenty. Then thin them out to 4cm apart and ensure they are growing in a sunny part of the greenhouse or windowsill (don’t forget to add the thinnings to your salad!).
why are my kale seedlings falling over?
Most of the brassica family are very shallow rooted, so they need to be planted deeply into firm ground to prevent root rock. They are often top heavy too, with their extravagant lush leaves being battered by the wind. It can be worth staking them with a cane if your garden is particularly windy, and this should keep them upright a bit longer.
frequently asked questions
why is kale good for you?
We have always known that it is good to eat your greens, and kale is perhaps the best green vegetable to eat – some people call it a ‘superfood’. It contains high concentrations of iron, calcium, vitamin C and vitamin K. It is also full of fibre and antioxidants.
how long does kale take to grow?
You can start harvesting kale at the micro-leaves stage and you can certainly eat the thinnings as a salad garnish if you have sown your seeds too thickly. Some varieties, like ‘KX1’, produce leaves for salads at four to six weeks, whilst others such as Nero di Toscana take a little longer to produce the long strap like leaves that are generally cooked in soups, stews or stir fries.
how tall does kale grow?
Some varieties, like ‘Nero di Toscana’, can get to 1.2m (4ft) tall, while its little brother ‘Black Magic’ is only half its height at 60cm (2ft), making it suitable for containers or window boxes. Check the seed packet for individual heights, and space your plants out accordingly.
how do I harvest kale so it keeps growing?
It is best to cut or snap the leaf stalks quite close to the stem, but only take about four leaves off per plant, so that each plant has enough leaves left to recover and produce more. You will find that kale actually goes quite a long way when you cook it – much further than spinach as its water content is much lower.
does kale need full sun?
Kale does prefer full sun, but you will get a crop in partial shade, just not such a prolific one.
does kale need netting?
If you are troubled by cabbage white caterpillars or pigeons then netting can be a solution. But remember that it does need to be really well sealed, and also, you need to get in yourself to pick your kale. Caterpillar squashing can be a better solution.
does kale need a lot of water?
You will need to water in your freshly transplanted seedlings, but after that they will only need a drink if there is a prolonged drought.
should I let my kale flower?
Being a biennial, you won’t really be able to stop it. Most brassicas are programmed to flower in their second year, so come April the plant will start to create buds and beautiful yellow flowers will appear. Do not despair though, as not only are all brassica flowers delicious and decorative on a salad, they are also excellent for pollinators and hoverflies. So, enjoy the sight and taste of the flowers before you pull up the plant and add to the compost heap.
You could even try collecting some ripe seed, to sow again for a new crop, but brassicas are very promiscuous so they are very unlikely to come true to type (fine for micro-leaves though).
will frost kill kale?
No, kale is extremely hardy, and frost only makes it tastier, increasing the sugars and decreasing the bitterness. The frost also looks exquisite on the crinkly curly kale leaves, making it an excellent addition to the winter garden.
what to grow with kale
Growing leeks or onions amongst your kale plants can help deter aphids and flea beetle as both are deterred by the smell. Some annual flowers such as marigolds will attract useful predators such as lacewings and hoverflies which will eat the aphids, as will the ever-useful ladybird.