Spinach is one of the more temperature-sensitive leafy greens in the home garden. It grows well in cool conditions but bolts to seed quickly once the weather warms up, so the sowing calendar looks different to most other vegetables.
In Auckland and the Bay of Plenty, sow from February right through to October. That covers autumn, winter and spring but skips the hottest months. In Waikato and Wellington, the window is February to September. Further south, in Canterbury and Otago, spinach does best sown in two shorter windows: March-April and again in August-September (extending to October in Canterbury). That avoids the coldest depths of winter as well as summer.
Spinach is quick to reward you: expect repeated pickings over four to eight weeks from a single sowing, with the first leaves ready in around 30-40 days. Space plants about 20cm apart and keep the soil evenly moist. Spinach growing in a partial-sun spot with consistent water holds its quality longer before bolting than spinach left to dry out in full sun.
Downy mildew and leaf spot are the main diseases to look out for, particularly in wet or humid weather. Aphids, leaf miner, and slugs and snails are the common pests. Good companions include cauliflower, celery, eggplant and strawberries. Avoid planting spinach near potatoes, sweetcorn, fennel or pumpkin.
If your spinach starts sending up a tall central flower stalk, that's bolting. It's a sign the weather has turned too warm. Pull it and resow once temperatures drop again, rather than trying to nurse it along.
If your spinach starts sending up a tall central flower stalk, that's bolting.