Spinach (Spinacia oleracea) is a leafy green vegetable that thrives in cool weather and short days. Although this crop seems made for our climate, it has a tendency to bolt (form flowers and go to seed). Bolting slows growth and makes the leaves bitter; as a result, many local gardeners steer clear of it.
How can you avoid a bolting experience and enjoy fresh spinach from your own garden? Here are a few tips.
Spinach tends to bolt when temperatures are warm and days are longer than 14 hours (beginning around April 21 in Clallam County). Because spinach germinates at relatively low soil temperatures (35 to 40 degrees), plant seeds as soon as the ground can be worked, at least 4-6 weeks before the last spring frost.
Plant spinach again in late summer (in August or September) as days shorten and temperatures cool, 6-8 weeks before the first frost. Fall-planted spinach that does not mature before the first frost will go dormant. If protected from rain, the plants will start growing again as temperatures increase in late winter and days get longer. Overwintered plants can provide one of the earliest spinach crops possible.
Planting and care
Plant spinach in full sun in well-drained soil high in organic matter. Because spinach is related to beets and Swiss chard, avoid planting it where these or other members of the Amaranthaceae family were recently grown.
Plant spinach seeds one-half inch deep and an inch apart in rows that are 18 inches apart. Overcrowding stunts growth and encourages plants to bolt, so thin plants to 4-6 inches apart when they have at least two true leaves.
Spinach has a relatively superficial root system and water stress (either too much or too little) will encourage plants to bolt. Provide enough water to keep the soil moist but not soggy. To help retain moisture, mulch the plants after thinning them.
Spinach is not a heavy feeder; fertilize with a nitrogen-based fertilizer only if plants are growing slower than expected or show signs of nitrogen deficiency (that is older leaves turning yellowish).
Spinach is a good source of vitamins A and C and is naturally high in fiber and low in cholesterol. Begin harvesting your spinach when the leaves are large enough for your tastes. To harvest, pull out the entire plant or remove the older outer leaves, allowing the younger inner leaves to continue growing.
You also can cut down the whole plant (in a cut-and-come-again fashion). If you cut about an inch above the base of the plant, it often will send out a new flush of leaves. Generally 3-4 weeks of re-growth are required before the second harvest yields an adequate volume.
Spinach varieties recommended locally for early spring planting include ‘Bloomsdale Savoy,’ ‘Olympia’ and ‘Space.’ ‘Bloomsdale Savoy,’ ‘Olympia’ and ‘Giant Winter’ are recommended for late summer/fall planting. ‘Giant Winter’ is cold hardy and recommended for overwintering.
Consider planting bolt-resistant varieties in late spring and early summer as temperatures warm. Bolt-resistant varieties tested by Oregon State University include ‘Correnta,’ ‘Spinner’ and ‘Tyee,’ although experiences with these varieties by local gardeners have been mixed.
Jeanette Stehr-Green is a WSU-certified Clallam County Master Gardener.