How to grow spinach

Spinach bolts in response to day length as much as heat — once days pass about fourteen hours it runs up a flower stem and stops making leaves, and nothing you do prevents it. In practice that means a spring sowing has a short window: a few weeks of picking in late spring, then it is over.

The autumn crop has no such limit. Sown from late summer, spinach sizes up as the days shorten, stands through the cold, and picks through winter and into the following spring — which is exactly the period when there is least else to eat from a garden.

The 1912 manual describes this as ordinary practice, and its account of large-scale growing near Norfolk, Virginia is worth knowing: cuttings made at any time during the winter when the fields are not frozen or covered with snow, and then a new flush of growth and a large crop of early greens when the weather moderates. That is a winter crop, not a spring one.

It also notes that three or four ounces of seed sown in autumn after a summer crop has come off will produce an abundance of greens for the average family — which is a good reminder of how little ground this takes.

In a mild maritime winter the plants simply stand. Where the ground freezes hard, a low tunnel or a thick straw mulch carries them through.

Sow direct — spinach has a taproot and resents being moved, so modules are more trouble than they are worth.

The one thing that stops a sowing is warm soil. Spinach germinates poorly above about 70°F and barely at all above 85°F, which is precisely the temperature a bed sits at in the late summer window when you most want to sow it. The practical answers are to water the drill heavily before sowing to cool it, to sow a little deeper than usual so the seed sits in cooler soil, to shade the row for the first week, or simply to wait for the first cool spell.

Sow about half an inch deep in rows a foot apart. Our calendar gives four inches between plants and fourteen between rows; the 1912 hand-cultivation column says rows twelve to eighteen inches apart at seven or eight plants to the foot. Sow thickly and thin by eating.

Seed keeps three to five years but germination falls off noticeably — if a sowing is patchy, suspect the seed before the soil.

Most modern advice says to pick outer leaves and leave the centre. The 1912 manual recommends the opposite and is, for a garden row, right: in gathering spinach the entire plant is removed rather than merely cutting off the leaves, the larger plants being selected first so the smaller ones are given room to develop. It adds, pointedly, that no thinning is required if this plan of harvesting is practiced.

That is a genuinely better method than it sounds. Harvesting whole plants largest-first thins the row and feeds you in the same motion, removes the fiddly business of picking individual leaves, and leaves a row that gets progressively better spaced as you eat it.

For a cut-and-come-again bed the leaf method still works — take a third at a time and never the growing point — but for a row grown to eat properly, whole plants are less work and better food.

Pick in the morning. Spinach wilts fast in warmth and a plant cut in the afternoon never crisps up again.

Spinach is a leaf crop grown fast, so it wants nitrogen and moisture and it wants both steadily. A plant that is checked by drought or hunger is smaller, tougher and closer to bolting than one that grew evenly.

It dislikes acid soil markedly — the same preference as its relative the beet — and a poor spinach crop on ground that grows everything else adequately is a reasonable prompt to test the pH.

Solomon's note is worth having for dry gardeners: spring spinach is remarkably more drought-tolerant than its delicate appearance suggests, and a bolt-resistant variety sown in late April at a foot apart in rows three feet apart can still be yielding pickable leaves in late June or early July with no watering at all. That is a very different plant from the crowded row most people grow.

Beet leaf miner is the one pest that genuinely matters, and it is the same insect that troubles beet and chard — unsurprising, since they are relatives. The larvae feed between the upper and lower surfaces of the leaf, making pale winding tunnels and then translucent blistered patches. On a root crop that is cosmetic; on a leaf crop it is the crop.

The only reliable control is exclusion: floating row cover from the day of sowing, on ground that did not grow spinach, beet or chard the previous year. That is what the fleece in the photograph at the top of this page is doing. Beyond that, pick off and destroy affected leaves as soon as you see a tunnel, which prevents the larvae completing their cycle in your bed.

Downy mildew shows as pale yellow patches on the upper leaf surface with grey fuzz beneath in prolonged damp — which is most of a maritime winter. Space rows so air moves, avoid overhead watering, and choose resistant varieties, which most modern spinach is.

Slugs take seedlings and, in a wet winter, mature plants sitting on wet soil.

Aphids gather in the crown. On a crop you eat raw this matters more than usual, so check before harvesting rather than after washing.