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Bountiful Fall Spinach

by John Navazio

Harvesting fall-planted Spinach, Decorah, Iowa

There's nothing better than the taste of home-grown spinach. Unfortunately, many gardeners who plant in spring are disappointed by meager harvests of small, tough leaves from plants that bolt (go quickly to the flowering stage) before producing large, juicy leaves.

If your spring-planted spinach never produces well, now is the time to plant it as a fall crop instead. Why? Because spinach is a cool-season crop that does best when days are less than 14 hours long and temperatures don't exceed 80oF. The best available time to get these conditions, especially in cold-winter areas (USDA Hardiness Zones 6 and colder), is to plant at the end of summer for a fall harvest. To determine the best planting time and varieties to use, I sowed several leading home garden varieties on different late-summer dates and compared notes with gardeners across the country following the same schedule. Here's what we found.

Why Does Spinach Bolt?

Why Does Spinach Bolt?
bolting spinach

Except in the South and Southwest (zones 7 and warmer), spinach has traditionally been planted in spring for harvest in early summer. But in these zones, it's sown from early October to mid-November for winter harvest starting six weeks later.

Two major problems with getting spring-planted spinach to grow well are day length and heat. While heat is usually thought of as the main cause of bolting, day length actually initiates this flowering response in spinach. Flowering in most varieties used in North America is "switched on" by days about 14 hours long--as early as the middle of May for many areas north of the 36 degrees latitude (roughly a line running from Washington DC to San Francisco).

By the time warm spring weather arrives and the spinach is growing nicely, the days have become long enough to initiate flowering. Then days above 80° F speed up the plants' metabolism, accelerating the rate of bolting.

Best Timing and Varieties

The solution is to plant a fall crop. For fall harvest in cold-winter areas, gardening experts usually suggest planting four to six weeks before a killing frost. This advice, however, is best suited to growing spinach to overwinter for an early-spring harvest (increasingly the case in Northern areas), not for a bountiful fall harvest. Chris Blanchard, a market farmer at Rock Spring Farm near Decorah, Iowa, plants his overwintering spinach between September 1 and 10 to get plants 5 to 6 inches in diameter by the time cold stops the growth."That's the perfect size for overwintering, but doesn't yield much spinach for a fall harvest," he says.

For a fall crop in my garden in coastal Washington state (zone 8), I decided to try planting earlier. I planted on August 1 and 15, 8 and 10 weeks, respectively, before our usual first frost in mid-October. For comparison I also planted on September 1, the usual sowing date for overwintering spinach crops in my climate. To find out if these earlier planting dates would work in other cold-winter areas, I enlisted David Cavagnaro, a horticultural photographer in Decorah, Iowa (zone 4), and Charlie Nardozzi, senior horticulturist at National Gardening in Burlington, Vermont (zone 4), to augment my plantings in Bellingham.

Once I had decided on the planting dates, I needed to pick the varieties. I chose a wide range including the savoyed (crinkly-leafed) 'Long Standing Bloomsdale' and 'Winter Bloomsdale', smooth-leafed 'Olympia' and 'Space', and the semi-savoyed 'Tyee', 'Coho', and 'Indian Summer'. On each planting date, we all planted 2- to 4-foot-long rows of each of these varieties.

Planting conditions is all three sites were similar. In general, fall spinach can be successfully grown on any fertile, well-drained soil with a pH between 6 and 7. It's best to plant in sandy loam in raised beds to keep the soil warmer and well drained, especially once the weather turns cold. Compost is an excellent soil amendment, providing a steady supply of nitrogen for luxuriant growth.

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