Loosen the soil in early spring or late fall, when temperatures are just above freezing. Work the soil for a depth of 4 to 6 inches, adding in 50 percent organic composted manure, mixing well with the soil.
Lay spinach seeds on top of the soil, spacing them approximately 8 inches apart. Lightly dust the soil/composted manure over the seeds, just barely covering them. Staggering plantings every 10 to 12 days will allow you to harvest spinach for a longer period of time.
Use a sprinkler to water your spinach seeds, getting the ground damp but not waterlogged. Keep the ground damp until the seeds sprout, which should be in seven to 10 days. Once sprouted, allow the ground to almost dry between waterings, never allowing the ground to become soggy.
Spinach should be planted in areas out of direct sun if possible. If this is not possible then put up barriers to the sun, allowing your plants to grow in the shade. Keep your plants as cool as possible. Liquid seaweed may be applied as a fertilizer if necessary, although composted manure should provide your spinach with all the nutrients it needs.
Warm weather will cause your spinach to send up tall stalks which will produce flowers and quickly go to seed. When stalks are dry, cut the seed pods and place them in a paper sack. Allow the pods to dry thoroughly, then slightly crush. Pour the contents onto a newspaper and separate out the tiny seeds. Save the seeds in a baggie in a cool, dry location until ready to plant.