Growing spinach in planters is more exacting than growing it in the ground. The smaller soil mass gains heat and looses moisture more rapidly than garden plot soil. Spinach needs ample moisture, good drainage and a minimum of six weeks of cool weather, with temperatures between 35 and 75 degrees Fahrenheit, from sowing seed to harvest. It bolts -- begins to send up a flower stalk -- when day length is over 14 hours. Warm weather speeds bolting, which makes spinach bitter and fibrous. Select spinach varieties that are slow to bolt and disease-resistant when planting a container garden.
Types of Spinach
There are three basic spinach types based on leaf texture: savoy, semi-savoy and smooth. Savoy spinach has crinkly puckered leaves and grows low to the ground, making cleanup of trapped soil particles a problem. Savoy varieties are cold-resistant, but savoy has low bolt resistance. Semi-savoy spinach has less crinkled taller leaves and varieties with both bolt- and disease-resistance. Smooth spinach has flat leaves. Varieties differ in bolt resistance. Areas with cool summers can often have and extended spinach-growing season.
Savoy Spinach Varieties
For fall sowing, seedlings must live through cold winter temperatures. To get a head start on your spinach crop, put "Bloomsdale" into one planter. It tolerates temperatures down to 15 or 20 degrees Fahrenheit. Planters are easy to cover for cold protection below that range. Once temperatures begin to warm, the seedlings grow quickly to give you an early spinach harvest. To extend savoy plantings later into the season, choose "Regiment" or "Spinner" for their resistance to blue mold and bolting.
Semi-Savoy Spinach Varieties
A variety that can be successively sown in planters for staggered year-long harvest in mild-winter climates is "Tyee." It has exceptional bolt resistance and is resistant to downy mildew strains 1 and 3. "Teton" is slow to bolt and resists downy mildew strains 1 through 4. In Colorado field trials, "Umbria" stood out as showing no blue mold or bolting at all and had good yield. Disease resistance is especially important in planters where air circulation is limited.
Smooth Spinach Varieties
Smooth leaf spinach varieties are more susceptible to bolting than semi-savoy types. "Emu" is the slowest bolting smooth variety. "Space" possesses moderate bolt resistance as well as resistance to strains 1 through 3 of downy mildew. "Python" has arrowhead shaped leaves and has wide disease resistance to strains 1 through 7, 9 and 11 of downy mildew. It and the round-leaf variety "Raccoon" are sown for fall harvest.
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