Spinach originated in Persia before being transported to China and Europe, then arriving in America during the 19th century. Despite early claims, spinach does not contain high levels of iron but is a rich source of beta-carotene, calcium and folic acid.
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Spinach is known as a heavy feeder and requires high levels of nitrogen for healthy growth and development. If using commercial fertilizer, 3-1-2 or 4-1-2 ratios of nitrogen, phosphorus and potassium, respectively, are recommended. If using organic fertilizer, blood and cottonseed meals, alfalfa pellets and fish emulsions are the best options. Spinach also requires adequate boron; if spinach appears stunted with dark roots and flattened yellow leaves, add 1 oz. of Borax every 100-square-foot row.
How to Apply
After transplanting young spinach plants, apply fertilizer evenly around plants. Four weeks later, a nitrogen-based fertilizer (21-0-0) should be spread to the side of the plants to promote speedy plant growth and strong leaf production. If using organic fertilizers, fish emulsion, seaweed and cottonseed meal are recommended. Fish emulsion should be mixed with water and poured into the soil surrounding the plants.
Spinach crops are typically harvested in the early spring and autumn; more fertilizer may be necessary for the spring crop than the fall one. Have soil tested for an accurate analysis of nutrient content to ensure fertilizer is not overapplied.