Spinach is a super-cold, hardy, leafy green, a popular crop that can be planted in very early spring and in the fall, and even the winter in some areas. It has similar cool-season growing conditions and requirements as lettuce.
Planting and Growing Information:
Spinach can deal with full sun to light shade. From seeding to harvest, spinach requires 6 weeks of cool weather, so be sure to sow seeds directly into the soil as soon as the ground warms to 40°F. To speed up its warming, cover the soil with black plastic. Spinach should have a neutral pH. While seeds can be started indoors, it’s not recommended because seedlings are difficult to transplant. In northern climates, gardeners can harvest early spring spinach if it’s plated just before the cold weather arrives in the fall. Protect the young plants with a cold frame or thick mulch through the winter, and then remove the protection when soil temperature in your area reaches 40°F in the spring. Remove the mulch to harvest some spinach and then replace the mulch. Common spinach cannot grow in midsummer. (For a summer harvest, consider New Zealand Spinach or Malabar Spinach, two similar leafy greens that are more heat tolerant.) For a fall crop, re-sow in mid-August when the soil is no warmer than 70°F. Sow seeds ½ of an inch deep every 2 inches and cover ½ inch of soil. Plant in rows 12 to 18 inches apart or sprinkle over a wide row or bed. For a continuous harvest, be sure to sow every couple of weeks during early spring.
Make sure to water the spinach to keep soil constantly moist. To maintain cool soil and deter pests, use row covers. Thin seedlings to 3-4 inches apart once they sprout to about 2 inches. No cultivation is needed beyond thinning because roots are shallow and easily damaged. To retain moisture, water regularly and mulch. Spinach can tolerate the cold in early spring and late fall, and it can survive a frost and temperatures down to 15°F. Since young spinach is more tender, be sure to cover it if cold temperatures are in the forecast.
Be sure to prepare soil about a week before planting by mixing in a combination of compost and a balanced fertilizer. Alternatively, prepare the soil in late summer or early fall, when spinach can also be sown where winters are mild. Once plants reach one-third of their growth, side-dress with a high-nitrogen fertilizer when necessary. Nutrient deficiencies may appear as yellow or pale leaves, stunted or distorted growth, a purpling or bronzing of leaves, leaves dropping early, and other symptoms.
To allow inner leaves to develop, harvest a few outer leaves from each plant when leaves reach desired size, or harvest the entire plant, cutting them stem at the base. Make sure to not wait too long to harvest or wait for larger leaves. After maturity, bitterness will set in quickly. Be mindful of day length and heat because increasing daylight (about 14 hours or longer) and warmer seasonal temperatures can cause spinach to bolt, which makes leaves taste bitter. Should the spinach start to bolt, pull the plant and use the leaves or attempt to slow the bolting by pinching off the flower/seed heads, keep the soil moist, and provide shade.