Popeye swallows them cans: green spinach leaves! Today we know that it is not the high iron content, but the nitrates it contains that can promote muscle growth. But the spinach has to be as fresh as possible. You can sow it in spring and autumn. For this you should look for a semi-shady place - either outdoors or indoors.
Tried and tested, high-yielding spring and autumn variety, bolt resistant, frost hardy, suitable for overwintering.