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 low tunnels for cold-hardy crops, which makes growing winter spinach easier than ever. 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 fall.
Create a Fertile Bed
In any season, spinach grows best when given rich, near-neutral soil that has been enriched 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-fertilized veggies like sweet corn, I have found that spinach benefits from having its soil amended with a thick blanket of garden compost and a balanced organic fertilizer.
Make Multiple Sowings
Spinach can have germination issues in any season, but in my experience germination is better in late summer than in spring, probably 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. Then there is the issue of when the spinach will mature. I make my first fall planting in August, but this sowing is intended for heavy harvesting in October. Spinach for growing through winter is best planted a little later, in September, so that the plants become established, bear one light harvest of baby greens in late fall, and then go into a state of semi-dormancy through the dark days of winter. Then, as soon as days become longer February and March, the plants will produce harvest after harvest of sweet, tender leaves until the plants bolt in late spring.
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.
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 row cover grows just as well as spinach grown in greenhouses or high tunnels. 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 I prefer a glass-topped cold frame because it stays put in high winds, and never collapses due to heavy snow. Because winter spinach stays so close to the ground, it is never cramped by the top of the frame.
Ventilation is crucial, 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.
Fertilize 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 vigor, well fed spinach plants produce larger leaves.
By mid 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.
By Barbara Pleasant