Why Won't My Spinach Seeds Germinate?

Spinach is generally willing to germinate, but it has a particular enemy: heat. Spinach seeds enter thermal dormancy at soil temperatures above about 25–28°C — the seeds simply refuse to germinate as a natural mechanism to avoid wasting energy in conditions too hot for the plant to survive. This makes summer sowing very difficult even if you do everything else right. Understanding the temperature link, along with other common germination failures, gives you the tools to succeed.

Thermal dormancy — the heat problem

If you are sowing spinach in summer and getting no germination, soil temperature is almost certainly the cause. Spinach germinates best between 7°C and 20°C, with the sweet spot around 10–15°C. Above 25°C, germination fails. In mid-summer, even in the UK, soil in a sunny spot can reach these temperatures in the top few centimetres. To germinate summer spinach, sow in a shaded spot, pre-cool the seed in the fridge for a few days before sowing (priming), water the drill with cold water just before sowing, and sow in the evening when soil is at its coolest.

Old or poorly stored seed

Spinach seed has a shorter viable lifespan than many vegetable seeds — it is generally reliable for two to three years but can decline after that, especially if stored in warm or damp conditions. Old seed from the back of a drawer may have germination rates well below 50%. Always sow more thickly with old seed to compensate, or simply buy fresh seed each year if spinach is an important crop. Store seed in a sealed container in a cool, dry, dark location to maximise longevity.

Sowing too deep or too shallow

Spinach seeds are larger than many salad seeds and need to be sown at about 1.5–2 cm depth. Too shallow and they dry out before germinating; too deep and they struggle to push through, especially in heavy or compacted soil. In a seed drill or tray, the compost or soil should be firmed lightly before and after sowing to ensure good contact between seed and the surrounding growing medium — seeds that are loosely surrounded by air gaps in the soil dry out quickly and fail. Water after sowing and keep the surface moist until germination.

Kale germination is much more reliable

Kale has none of spinach's heat-dormancy issues and germinates over a wide temperature range from about 5°C to 30°C. If you are struggling with spinach germination in summer, kale is a practical alternative for the warmer months and provides a similar leafy harvest once established. Kale seeds sown in modules or direct in June and July establish well and are ready to harvest from autumn onwards.