Kale is considered an easy plant to grow in the UK climate. It will tolerate a wide range of both soil and temperature conditions. There are many different varieties to choose from. Broadly, the most common types are curly kale and cavolo nero.
Kale prefers a loamy, well drained soil – moist but not soggy. Some good compost and fertiliser will get it off to a good start, but it doesn’t require high levels of nitrogen.
Differences in conditions affect the taste. It’s considered a cool weather plant and tastes sweeter after a touch of frost. Conversely it will taste more bitter in hot weather. It likes to be in the sun, but prefers temperatures below 27ºC (80ºF). It will continue to grow in temperatures down to -7ºC (20ºF).
Kale is a biennial plant so it’s designed to grow all through the winter and not run to seed until the following summer.
Plant in the spring, from late March onwards. The ideal germination temperature is 21ºC (70ºF) but it will germinate from 4ºC (40ºF). If you eat a lot of kale in warmer months, it’s worth sowing some more later in the summer to get you through the winter.
If you want to get it off to a quick start, sow the seeds in pots of compost, either in the house, in a shed or in a greenhouse. Otherwise they can be sown directly into the soil, but will take longer to germinate.
Harden off the seedlings by putting them outside for a few hours every day for about a week, so they can adjust to the outdoor conditions. Plant them out when they are about 4-5” tall, leaving at least 12” between plants.
Like all brassicas, kale will be hungry for nitrogen. Grass is rich in nitrogen, so if you have a lawn, an easy way to get some back into the soil is to use grass cuttings.
Ideally, spread the cuttings out and dry them in the sun or a warm, well-ventilated place. They should turn dry and dark green within a day or so (longer in cooler weather), and you can sprinkle them onto the soil around the plant. If you like, you can dig them in, or just let the worms do the job.
In wetter weather, you can still use cuttings as a mulch, but they’ll turn yellow and smell a bit strange. Make sure you just add a thin layer, or it can go slimy and attract slugs.
Obviously if you’re gardening organically, it’s important only to use grass that hasn’t been treated with chemicals such as weed-killers.
We use Vitax Organic Liquid Seaweed as a feed every fortnight when the kale is at its most prolific. It’s rich in potassium, magnesium and trace elements. We’re also experimenting with Emiko EM-1 – a kind of probiotic for the soil. More about that at a later date.
Start harvesting leaves when they’re about the size of your hand. Just cut the whole leaf off with a pair of sharp scissors or secateurs, close to the main stalk but not so close as to cause damage. Always harvest from the bottom – don’t cut out the top leaves or the plant will stop growing.
Remove any yellow or brown leaves, or stems from previous harvesting while you’re there.
Cabbage whitefly and mealy cabbage aphid (pictured below) are the most common pests with kale. The latter lay these grey ashy eggs in big clusters, making the plant shrivel up, which is a real nuisance.
Marigolds are a good deterrent for aphids, so companion planting is worth considering. Marigolds also attract ladybirds, which eat aphids.
Cabbage white caterpillars will also have a go, if they can’t find any cabbage or kohl rabi. Black and yellow ones are from the large cabbage white butterfly. The small cabbage white has fuzzy green caterpillars.
They look cute, but they’re greedy, and the green ones are especially hard to spot. Wherever you see sizeable holes in the leaves, and the brownish green pellets they leave behind, you’ll probably find them – usually on the underside of the leaf. Pick them off by hand (or by forceps if you’re squeamish like me). What you do with them then is down to your own conscience 🙂
Prevention is better than cure, so if you can net your brassicas, you’ll deter cabbage whites at the butterfly stage. They’re persistent though, and will lay eggs through netting if the leaves are close enough. Ideally, catch them at the egg stage then – they’re really easy to spot if you check the underside of the leaves. They’re bright yellow or white, and are usually laid close together in neat groups. Just brush them off with your fingers (or a cloth in my case).
If the kale is left un-netted, wood pigeons might help themselves, and they’re more destructive than any other pest. They struggle to land on the plant itself, but if there’s anything they can use as a perch nearby, will happily munch away at any brassica.
We spray all our brassicas with a weak solution of organic neem oil and Dr Bronner’s Castile Soap – preferably peppermint, as that’s especially distasteful to bugs. Mix 1/4 tsp of the neem and 1/8 tsp of the soap with 200ml of water. Use a spray bottle with a fine mist setting. It’s important to spray underneath the leaves as well as the tops. Repeat every day or two.
Got any tips or questions of your own about growing organic kale? Leave us a comment below, we’d love to hear from you.