How to grow broccoli

Broccoli makes its head — which is a mass of unopened flower buds — and it wants to do that in cool weather. Push a plant into head formation during a hot spell and it either makes a small loose head that flowers almost immediately, or it skips the head and bolts straight to flower. Nothing about feeding, watering or spacing rescues a crop that heads in August.

This is why the autumn crop is usually the better one, and why experienced growers in mild climates lean on it. A summer sowing sizes the plant up through warm weather and forms its head as things cool down, which is exactly the right way round. The spring crop has to race — it must be big enough to head before the heat arrives, which means starting early under cover and getting it out as soon as the ground allows.

In the maritime Northwest this lines up unusually well. The cool, long spring is good for an early crop, the genuinely hot weeks are few, and the mild autumn lets a late crop head in comfort. Overwintering types take it further still: purple sprouting broccoli sown in spring occupies its ground for nearly a year and gives you shoots in March and April, which is the hungriest part of the growing year.

Broccoli transplants willingly, which is why almost everyone starts it in trays or a nursery bed rather than direct-sowing. Sow a quarter-inch deep, expect germination in under a week in warm soil, and grow it on with plenty of light — a broccoli seedling that stretches for light makes a weak, leggy plant that never quite recovers.

Set plants out at about four to six weeks old, when they have three or four true leaves. Bury them slightly deeper than they sat in the tray, right up to the first leaves, and firm them in hard. Firm really does matter for the cabbage family: a loose-planted brassica rocks in the wind, the stem chafes, and the plant sulks all season. The old advice was that you should be able to tug a leaf and tear it rather than lift the plant.

Solomon's method for dry gardening is the opposite and worth knowing: sow a pinch of seed directly onto a deeply dug, well-fertilised spot, then thin gradually to the single best plant by the time it has three or four true leaves. That gives an undisturbed taproot, which matters enormously if the plant will never be watered — and matters much less if it will.

Broccoli is a hungry plant and a big one. It wants soil with real fertility in it — compost or well-rotted manure dug in ahead of planting, and a nitrogen-leaning feed once it is growing away. Underfed broccoli makes a small head and stops, and unlike root crops there is no way to disguise it.

It also wants firm ground rather than fluffy ground, which is the opposite of what carrots want and surprises people who garden by one rule. Tread the bed or let it settle for a few weeks before planting.

Lime matters. The cabbage family prefers soil that is not acidic — somewhere around neutral — and acidic soil is both the maritime Northwest's default and the condition that clubroot thrives in. A soil test is worth doing once; it is the single most useful thing you can know about a brassica bed, and it saves guessing for years afterwards.

Space them further apart than looks reasonable. Our own figure is eighteen inches in the row with thirty between; Solomon, growing without irrigation, gives each plant three to four feet and argues that big plants make big sweet heads while cramped ones make small woody ones. The truth is that broccoli spacing is really a decision about head size.

This is the real work of growing broccoli, and it is why row cover is close to standard practice. The cabbage family is host to a well-organised set of pests, and in a home garden three of them account for nearly all the damage.

Cabbage white caterpillars — the green ones from the small white butterfly and the hairier ones from the large white — shred leaves and then burrow into the head, which is what turns a good harvest into an hour at the sink. Fine mesh laid over hoops from planting day prevents the butterfly ever laying, and is far more effective than anything you can do afterwards. Where they get in, Bacillus thuringiensis is the standard organic answer, and hand-picking works on a small planting.

Cabbage aphids form dense grey-white colonies in the growing point and among the buds. They are difficult to wash out of a head, so catch them early on the undersides of leaves. A strong jet of water knocks them down; encouraging the ladybirds and hoverflies that eat them does the rest.

Slugs and snails take young transplants, sometimes overnight. This is the pest that decides whether a planting establishes at all, and the damage is unmistakable — ragged holes in the middle of leaves rather than at the edges.

Two soil-borne problems worth naming: clubroot, which distorts the roots and is essentially permanent once present, controlled by liming and long rotations and by never bringing in soil or plants from an infected garden; and cabbage root fly, whose maggots attack the stem base and which a simple collar of card or felt around each stem prevents.

Cut the main head while the beads are still tight and matt. The moment they start to loosen and shine, and certainly the moment you can see yellow, the plant is opening its flowers and the texture has gone. This happens faster than people expect in warm weather — check every couple of days once a head is sizing.

Cut it with four or five inches of stalk and cut at a slight angle so water runs off the cut rather than sitting on it and rotting the stem.

Then leave the plant. Removing the main head releases the buds lower down the stem, and a good variety will produce side shoots — smaller, looser, and in most people's opinion better eating — for several weeks afterwards. Keep cutting them and the plant keeps making them; stop, and it flowers and gives up. On a home scale the side shoots often add up to more than the head did.

A trick worth knowing at the end of the season: a heavy feed when the autumn rains return can push a spent plant into a second flush of shoots from buds near the soil. Solomon suggests exactly this, and calls it taking a chance, which is the right level of confidence.

This is worth a moment because it explains why old gardening books seem to give strange advice about a familiar plant.

Our 1912 manual has no broccoli row in its planting table at all — cauliflower is there, Brussels sprouts are there, broccoli is not. Its broccoli section describes something else: a hardier relative of cauliflower, sown in spring, set out in June or early July, standing all winter and producing heads from midwinter into May, with the outer leaves folded over the head to protect it from frost. That is a description of overwintering heading broccoli, not of the green Italian type.

Burr in 1863 goes further. He describes twenty-five broccolis and every one is that older kind — white, purple, cape, sulphur — and most carry English breeders' names. The green sprouting calabrese that the word now means is simply absent from an exhaustive 1863 catalogue of American vegetables.

So when a pre-war book tells you to sow broccoli in spring for a harvest next April, it is not wrong and it is not talking about your seed packet. The nearest thing still sold is purple sprouting broccoli, which is grown on exactly that timetable — and which is, for that reason, the most historically continuous thing you can put in a brassica bed.