The trick to growing spinach is to grow it fast and harvset it fast, and use the right varieties in the right season. Spinach bolts as the days get long and when the weather gets hot. That's why spinach is usually grown in early spring and fall, in low temperatures and short days. Some varieties ddo a little better in long day, hot conditions. Pick them promplty in hot weather. For summer harvests, try New Zealand Spinach.
Season & Zone
Season: Cool season
Exposure: Full sun to partial shade
Spinach does best in cool weather. Direct sow March 1 to April 15. For late spring and early summer plantings use Tyee, and for quick harvest use Space and Olympia. Spinach will bolt once days get long and hot. Some varieties grow enough to harvest before they bolt. For continuous supply, plant every 3 weeks.
Sow again in the middle two weeks of August for a fall crop that, if cut at the soil level, will come back early the following spring. Shade summer-sown seed beds, keep very well watered, and sow more seeds than you need, as warm soil will reduce germination rates marginally. Thin seedlings, and use cloche protection as cold weather approaches. Late sowings like this can be harvested into December - in mild winters if cloche protection is provided.
Optimal soil temperature: 5-20°C (45-70°F). Seeds should sprout in 7-14 days.
Sow seeds 2cm (1") deep, 10 seeds per 30cm (12"), in rows 30-45cm (12-18") apart. Thin to at least 5-8cm (2-3") between plants, or further if you want larger leaves.
Ideal pH: 6.0-6.5. This heavy feeder requires rich soil. Dig in ¼-½ cup complete organic fertilizer beneath every 1m (3') of row. Overwintering spinach requires well drained soil.
For baby greens, pick when the leaves are 7-10cm (3-4") long. Individual leaves can be picked at anytime, until the plant has started to bolt. Cut the whole spinach plant just above soil level.
In optimal conditions at least 65% of seeds will germinate. Usual seed life: 3 years. Per 100' row: 400 seeds, per acre: 174M seeds.
Diseases & Pests
Pale, soft tunnels on leaves are probably leaf miner damage. Prevent be covering with floating row cover. You can kill the little insect causing the damage by pinching it inside the leaf. Destroy any affected leaves. Downy mildew is a fungal disease that causes grayish mould on the leaves. To avoid it, provide ample ventilation and avoid overhead watering.