Why does my spinach bolt almost as soon as it is up?

This is the crop where the standard bolting advice — keep it cool, keep it watered — largely fails, because the trigger is different. Spinach measures the length of the day. Once the days pass a threshold in late spring the plant switches to flowering, and no amount of shade or water stops it.

Step by step

1. Sow at the right end of the year.Early spring, as soon as the soil is workable, for a spring crop; and late summer into early autumn for a crop that picks through autumn, winter and the following spring. Those are the two windows where the daylength works with you.
2. Avoid sowing from late spring to midsummer.Sowings made as the days approach their longest bolt almost immediately whatever you do. That is not a failure of technique.
3. Switch crops for the summer months.Perpetual spinach (leaf beet) and chard are beet-family plants, not true spinach, and they crop right through the summer without bolting in the same way. New Zealand spinach also holds through heat.
4. Sow direct and thin, rather than transplanting.Spinach dislikes root disturbance, and a checked plant bolts sooner. Sow where it will grow and thin to about 15cm.
5. Keep it moist and fed.Water and nitrogen do not override daylength, but a dry, hungry plant bolts even sooner than the daylength alone would dictate. Steady moisture and a fertile soil buy you time.
6. Pick regularly and hard.Taking outer leaves every few days keeps the plant in a vegetative state a little longer, and gives you the crop before the plant makes its decision.
7. Choose bolt-resistant varieties for spring sowings.Varieties bred for bolting resistance genuinely last longer in the spring window, though none of them will hold through midsummer.
8. Use the autumn sowing under cover for winter picking.A late-summer sowing under a cloche, in a cold frame or in an unheated greenhouse gives leaves through winter and a big flush in early spring before it bolts.

Tips

• The pattern is easy to remember: true spinach at the ends of the year, chard and leaf beet in the middle.
• Spinach sown in autumn under cover is one of the most productive things you can do with a cold greenhouse or a cloche.
• Bolted spinach leaves go bitter and tough. Once the flower stem is up, clear the plant and re-sow — it will not recover.
• Baby leaf spinach for salad is sown thickly and cut young, so it is harvested before bolting matters — a good use for the awkward months.
• Downy mildew is the other common spinach problem, showing as pale patches with grey mould underneath. Space plants for airflow and grow resistant varieties.

Common mistakes

• Treating it like lettuce and adding shade — Lettuce bolts on heat, spinach on daylength. Shading does not shorten the day and the plant bolts anyway.
• Sowing the packet in May because that is when the garden is being planted — It is exactly the wrong month. Sow in early spring or late summer instead.
• Transplanting seedlings raised in modules — Root disturbance is a check, and a checked spinach plant bolts sooner. Sow direct.

Questions people ask