Growing guidelines: Overcrowding stunts growth and encourages plants to go to seed. To avoid crowding, thin seedlings to 4 to 6 inches apart once they have at least two true leaves. Fertilize with compost tea or fish emulsion when the plants have four true leaves.
Since cultivating or hand pulling weeds can harm spinach roots, it’s best to spread a light mulch of hay, straw, or grass clippings along the rows to suppress weeds instead. Water stress will encourage plants to bolt, so provide enough water to keep the soil moist but not soggy. Cover the crop with shade cloth if the temperature goes above 80°F.
Problems: Since most spinach grows in very cool weather, pests are usually not a problem. Leafminer larvae can burrow inside leaves and produce tan patches. Prevent leafminer problems by keeping your crop covered with floating row cover. For unprotected plants, remove and destroy affected leaves to prevent adult flies from multiplying and further affecting the crop. Slugs also feed on spinach.
Spinach blight, a virus spread by aphids, causes yellow leaves and stunted plants. Downy mildew, which appears as yellow spots on leaf surfaces and mold on the undersides, occurs during very wet weather. Reduce the spread of disease spores by not working around wet plants. Avoid both of these diseases by planting resistant cultivars.
Harvesting: In 6 to 8 weeks you can start harvesting from any plant that has at least six leaves 3 to 4 inches long. Carefully cutting the outside leaves will extend the plants’ productivity, particularly with fall crops. Harvest the entire crop at the first sign of bolting by using a sharp knife to cut through the main stem just below the soil surface.