Curly kale

Light and exposure

Kale likes full sun, but it makes do with light shade without any fuss. Allow at least five to six hours of direct light for stocky, well-leafed plants. In deep shade it stretches and turns lanky.

Give it room and air. A mature plant easily takes up half a metre across, and good airflow around the foliage limits the standing damp of a long, wet autumn. In an open, wind-exposed spot, earth up the base a little or stake tall plants so they do not topple.

Watering

During establishment and all summer, keep the soil cool and moist. A young plant short of water stays stunted and gets off to a poor start. Water generously at planting, then regularly in dry weather, preferably at the base so the foliage can dry off.

In autumn and winter, seasonal rain takes care of everything and there is nothing more to do on that front. The only risk at this season is not drought but excess water on heavy soil: good drainage then matters more than a watering can.

Soil and repotting

Kale is a hungry crop and likes rich, deep soil well supplied with organic matter. A dose of ripe compost or well-rotted manure the previous autumn, or at planting, sets it up in the best conditions. Cool clay soils suit it perfectly, as long as they drain.

It prefers fairly firm ground over soil that is too loose: a well-anchored plant stands up better to wind and to lodging. Aim for a neutral to slightly alkaline pH. A light liming, besides feeding the soil structure, discourages clubroot, which hates limey ground.

Temperature and humidity

This is where kale shines. It grows happily in the cool of spring and autumn, and takes frosts down to minus 10 degrees without damage, sometimes lower once well rooted. The hardiest varieties withstand even sharper cold snaps.

Better yet: do not harvest before the first frosts if you can wait. Frost turns part of the starch in the leaves into sugars, the bitterness recedes and the flavour clearly sweetens. It is the only vegetable in the garden that you actually want to let get cold before eating. In USDA zone 8 and milder, it comes through winter outdoors without protection in the vast majority of cases.

Pruning and upkeep

You do not really prune kale, you harvest it, and that harvest doubles as pruning. Take the leaves one by one, starting with the lowest and oldest, always leaving the central crown intact. The plant then keeps rising and producing new leaves from the top, sometimes for months.

Remove the yellowed or damaged lower leaves as you go: they are no longer useful and shelter slugs and disease. A regularly picked plant takes on the odd shape of a little palm tree, with a bare stem topped by a tuft of curly leaves, which is perfectly normal.

Pests and diseases

Kale’s enemies are those of the whole family. The cabbage white, that white butterfly whose green caterpillars devour the foliage, is worst through summer and into early autumn: inspect the underside of the leaves and remove the yellow egg clusters, or lay an insect-proof mesh over young plants. The mealy cabbage aphid forms grey, powdery colonies in the heart of the leaves and weakens the plant; a jet of water, ladybirds and removing the clusters see them off.

The real soil trap is clubroot, a fungus that swells the roots into galls and makes the plant waste away. It is hard to correct once established, hence the importance of prevention: keep a strict rotation, do not put brassicas (nor radish, nor turnip) in the same spot for three to four years, and keep the soil well drained and not too acidic.

Propagation

Kale is propagated from seed, and it is easy. Sow in a nursery bed or in pots from mid-spring to early summer, barely covered under half a centimetre of soil, somewhere cool. Emergence takes about ten days. Then transplant the young plants into place once they have four or five true leaves, spacing them well at 40 to 60 centimetres.

Set them a little deeper than they were in the pot, up to the first leaves: kale likes to be planted deep, it anchors better and stands up to wind. Firm the soil well around the collar and water to bond the earth to the roots. If you want your own seed, let a fine plant run to flower in the spring of its second year, but be aware that it crosses readily with the neighbouring brassicas.

Month-by-month care calendar

Green Hub tips

• Do not harvest too early: wait for the first frosts, the cold turns starch into sugars and takes away the bitterness.
• Always pick leaf by leaf from the bottom up, leaving the central crown: a single plant then produces for months.
• Plant deep, up to the first leaves, and firm the soil well: a well-anchored kale does not lodge in autumn storms.
• Keep a strict three-to-four-year rotation with no brassicas in the same spot, it is the only real defence against clubroot.
• An insect-proof mesh laid from the first butterfly flights until the end of summer settles the cabbage white problem in one move, with no treatment at all.