Spinach does best in cool weather. Direct sow in the period four weeks before, and three weeks after the last frost date. 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 where winters are mild. 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.