How to grow kale

Kale will grow perfectly well from a spring sowing and give you leaves all summer, and almost nobody should do that. It is at its worst in warm weather — tougher, more bitter, and a magnet for every cabbage-family pest at the point in the year when they are most active — and at its best after frost, when there is nothing else to pick.

So the useful sowing is late spring to midsummer, timed so the plants reach a decent size before growth slows in autumn. From there they stand, and you pick through the cold months.

Frost genuinely improves it, and the mechanism is the same one behind sweet parsnips and post-frost carrots: cold triggers the plant to convert stored starch into sugars, which work as antifreeze in the leaf. You taste the result. A kale leaf in November and the same leaf in August are different vegetables.

In a mild maritime winter the plants simply stand in the ground and are picked as needed, which makes kale the closest thing to a free winter vegetable there is.

Solomon ranks the brassicas by how well they dry-garden and puts kale at the head of the list — above late Brussels sprouts, late savoy cabbage, rutabaga and kohlrabi, and well above ordinary cabbage, cauliflower and Italian broccoli. His explanation is that the further this family has been bred from the wild cabbage, the more it has lost the ability to forage, and kale has been bred the least.

The practical consequence is a genuine option in a rainless summer: give the plants real room — Solomon says four feet, grown like broccoli — and they will sit stunted and gnarly through the drought without dying, then grow explosively as soon as the autumn rains return. A side-dressing of fertiliser in late September turns that recovery into a very large plant by November.

Our own calendar gives kale twelve inches in the row with twenty-four between, which assumes you will water. The 1912 table's hand-cultivation column says eighteen to twenty-four inches each way. The three figures are not in conflict — they are three different answers to the question of how much water the plant will get.

Everything true of the cabbage family is true here. Kale wants ground that has settled rather than freshly forked, soil that is not acid, and firm planting — a loose-set brassica rocks in the wind, chafes its stem and sulks.

It is a big plant and a tall one. A full-grown curly kale is a couple of feet across and, in a mild winter, will keep going into a second season and get taller still. Plant it where a two-foot plant in November will not shade something that needs the light.

Feeding is moderate rather than heavy. Kale is less hungry than cabbage or broccoli because you are harvesting leaves progressively rather than asking it to build one large structure. Too much nitrogen produces soft growth that aphids find first and frost damages more easily.

Kale grows from a single point at the top of its stem and produces leaves outward and downward from there. So the way to harvest it is to take the older, lower leaves and leave the growing point alone — do that and one plant keeps producing for months.

Take no more than about a third of the leaves at once. Strip a plant bare and it takes weeks to recover; take a few leaves a week and it barely notices.

The lowest leaves yellow and go tough as the plant grows on. Take those off whenever you see them, whether or not you want them — leaving them encourages slugs and holds moisture against the stem.

In spring, an overwintered plant will start to bolt and send up a flower stalk. Do not pull it immediately: the flowering shoots are excellent eating at the bud stage, essentially a sprouting broccoli, and a plant will give a fortnight of them before the stems get woody.

The two that matter are cabbage aphids and cabbage white caterpillars, and between them they account for nearly all kale damage.

Cabbage aphids are the more serious because of where they sit. Grey-white colonies pack into the crinkles of curly varieties and down into the growing point, where washing them out is close to impossible — a badly infested plant is effectively finished. Check the growing point and the undersides of young leaves weekly through late summer, blast early colonies off with water, and leave the ladybirds and hoverflies alone to do the rest. Flat-leaved types like cavolo nero are markedly easier to clean than curly ones, which is a real argument for growing them.

Caterpillars shred leaves, as the photograph below shows, but rarely kill a plant. Fine mesh over hoops from planting day is the reliable prevention; hand-picking works on a few plants and Bacillus thuringiensis on more. Kale's saving grace is that it grows through the damage — a plant that looks ruined in August is usually fine by October.

Whitefly rise in clouds when you brush the plants and look alarming. On kale they are mostly a nuisance rather than a threat.

And clubroot, which applies to every brassica: soil-borne, permanent once present, managed by liming towards neutral and by the longest rotation you can manage.