Spinach helped launch my career as a garden writer, because my first published article was on growing winter spinach. Much has changed since then, especially the use of polytunnels and low tunnels for cold-hardy crops, which makes growing winter spinach easier than ever. The payoffs can be huge, both in terms of quantity and quality. Overwintered spinach plants produce a bumper crop in spring, and because spinach uses natural sugars to protect itself from cold, winter spinach also has remarkably sweet flavour.
With a few decades of spinach-growing behind me, in several different gardens, here are my top tips for getting great crops from spinach planted in the autumn.
1. Create a Fertile Bed
In any season, spinach grows best when given rich, near-neutral soil that has been enhanced with composted manure or other nitrogen source, and this is especially important when growing winter spinach, which will stay in the ground for up to seven months. Even when planting spinach after heavily-fertilised veggies like sweetcorn, I have found that spinach benefits from having its soil amended with a thick blanket of garden compost and a balanced organic fertiliser.
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Winter spinach growing in a glass-topped cold frame
2. Make Multiple Sowings
Plant spinach twice in early autumn, making one sowing in late August for harvesting in October, and a second two or three weeks later for growing through winter. While fully-grown spinach plants often will overwinter successfully, the best prospects come if your spinach is holding only a few leaves when short, cold days stop plants from making new growth.
Spinach can have germination issues in any season, but germination is better in late summer than in spring due to warmer soil temperatures. But very hot weather also can lead to spotty sprouting, so you may need to sow seeds more than once to get a good stand.
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Spinach seeds germinate quickly in summer-warm soil
3. Thin to Keep Plants Healthy
Crowded spinach plants tend to stay wet for prolonged periods of time, which can lead to problems with a number of diseases that plague winter spinach. Most of the spinach varieties gardeners like to grow, including ‘Bloomsdale Long Standing’ and ‘Giant Winter’ (also called ‘Viroflay’) are susceptible to downy mildew, so it’s important to keep plants thinned and weeded to help fresh air circulate through the leaves.
4. Use a Low Tunnel or Cold Frame
Several recent research projects in the US have found that winter spinach grown in a low tunnel covered with horticultural fleece grows just as well as spinach grown in greenhouses or polytunnels. In addition to moderating temperatures, low tunnels shelter winter spinach from ice and snow, and keep the leaves reasonably dry as well. I have experimented with many different setups, and have found that spinach cannot tell the difference between a glass-topped cold frame or horticultural flece.
Choose a setup you can ventilate, because winter spinach growing in a low tunnel or cold frame can quickly overheat on sunny winter days. However, even with good weather, spinach and other cold-hardy greens will produce little new growth during the short days of December and January. Then, when days lengthen in February and March, the plants will produce excellent harvests of crisp leaves.
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Freezing weather triggers the production of natural sugars in spinach leaves
5. Fertilise in Late Winter
Winter spinach commences vigorous new growth at a time when soil temperatures are so low that the availability of nitrogen is limited. To meet the plants’ nutritional needs it is important to provide a booster feeding with a water-soluble plant food as soon as new growth appears in late winter. In addition to preserving plant vigour, well fed spinach plants produce larger leaves. March and April are prime harvest months for overwintered spinach.
By late spring, the combination of longer days, higher temperatures, and exhaustion cause winter spinach plants to grow tall and bolt, which earns them a place in my compost heap. By then I have spring-sown replacements in progress that will keep me supplied with spinach until chard season starts in early summer. I do not think it is possible to grow too much spinach.
Article last updated in 2022.
