Spinach is a leafy green flowering plant native to central and western Asia.
 
Spinach is one of the few vegetables with beets and chard that prefers a neutral to alkaline soil (pH 7.0 or above). If your garden soil is sandy and acid, be sure to get a lime recommendation based on a soil test before planting spinach. Spinach is also a heavy feeder. Start by working 2-4 pounds of a complete fertilizer per 100 square feet into the soil at planting time and then side-dress every two weeks or as necessary to keep the plants growing vigorously. Be sure to keep fertilizer 4-6 inches from the base of the spinach plants so as not to burn the roots and water thoroughly immediately after fertilizing.
There is no such thing as putting too much compost in garden soil. Mix at least 2-4 inches of compost in the row before planting. Commercial compost is sometimes little more than slightly decayed wood chips. Check to see that the raw material used to make the compost is mostly unrecognizable before buying it or better yet, make your own.
Spinach thrives in cool weather and short days so it's best to grow it in the fall for most gardeners. Northern gardeners can plant an early spring crop followed by another in midsummer to mature before the first hard freeze. In southern gardens spinach easily tolerates a light frost, especially if it is acclimated. In case of a sudden or hard freeze (below 28 degrees), old blankets or polypropylene frost blankets can save the day and prolong the harvest.
Plant spinach seeds an inch apart in rows 14-18 inches apart and cover the seeds with a 1/2 inch of soil. Keep the soil moist and after the seeds germinate thin them to stand 3-5 inches apart. Most gardeners like to do this in several passes to determine the strongest plants to save. Thinning is very important and you must be ruthless in the final analysis or you will have a congested row of plants that don't size up.