Spinach growing problems are often related to growing spinach in the wrong season.
Grow spinach in cool weather. Sow spinach in the garden as early as the ground can be worked in spring. Make succession sowings every 10 days for a continuous harvest of young tasty leaves. Continue sowing spinach until just a few weeks before the start of summer.
Sow spinach again in late summer for a cool fall harvest. In mild winter regions, sow spinach in autumn for spring harvest.
For spinach growing tips see Spinach Growing Success Tips at the bottom of this post.
Common spinach growing problems with cures and controls:
• Seedlings fail to emerge; poor germination. Seed sown too shallow. High temperatures or dry conditions will cause seed to dry and fail to germinate. Sow seed in cool weather. Keep soil evenly moist to allow for germination.
• Plants are eaten or cut off near soil level. Cutworms are gray grubs ½- to ¾-inch long that can be found curled under the soil. They chew stems, roots, and leaves. Place a 3-inch paper collar around the stem of the plant. Keep the garden free of weeds; sprinkle wood ash around base of plants.
• Seeds rot or seedlings collapse with dark water-soaked stems as soon as they appear. Damping off is a fungus that lives in the soil, particularly where humidity is high. Do not plant in cold, moist soil. Make sure soil is well drained.
• Leaves are faded yellow. Nitrogen deficiency. Spinach is sensitive to inadequate nitrogen. Side dress with compost tea every 10 to 15 days. Add aged compost to planting beds twice each year.
• Plant bolts–flowers and sets seed–before leaves are ready for harvest. Bolting can be brought on by long daylight and very warm temperatures or cool temperatures followed abruptly by very warm temperatures, 80°F or greater. Plant spinach so that it comes to harvest in cool weather. Plant varieties that resist flowering–bolting: Bloomsdale Long Standing, Big Crop, America. Plant spinach in late summer so that plants mature in the cool days of fall.
• Leaves curl under, deformed, and yellowish; small shiny specks on leaves. Aphids are tiny, oval, and yellowish to greenish pear-shaped insects that colonize on the undersides of leaves. They leave behind sticky excrement called honeydew which can turn into a black sooty mold. Remove aphids from leaves with a blast of water from the hose. Use insecticidal soap.
• White thread like tunnels within leaves. Leafminer larvae tunnel inside leaves. Destroy infected leaves and cultivate the garden to destroy larvae and keep adult flies–they are black with yellow stripes–from laying eggs. Cover crops with floating row covers.
• Tiny shot-holes in leaves of seedlings. Flea beetles are tiny bronze or black beetles a sixteenth of an inch long. They eat small holes in the leaves of seedlings and small transplants. The larvae feed on roots of germinating plants. Spread diatomaceous earth around seedling. Cultivate often to disrupt life cycle. Keep garden clean.
• Irregular small holes eaten in leaves. Cabbage lopper is a light green caterpillar with yellow stripes running down the back; it loops as it walks. Keep garden clean of debris where adult brownish night-flying moth can lay eggs. Cover plants with spun polyester to exclude moths. Pick loppers off by hand. Use Bacillus thuringiensis. Dust with Sevin or rotenone.
• Leaves are chewed. Snails and slugs feed on leaves. Hand pick at night when these pests feed or set out saucers of beer at soil level to attract and drown slugs and snails.
• Leaves and stems are partially defoliated. Armyworms are dark green caterpillars the larvae of a mottled gray moth with a wingspan of 1½ inches. Armyworms mass and eat leaves, stems, and roots of many crops. Armyworms will live inside webs on leaves. Handpick caterpillars and destroy.
• Plant yellows on one side; plant is stunted are stunted. Fusarium wilt or fusarium yellows, also called spinach yellows, is a fungal disease which infects plant vascular tissues. Fungal spores live in the soil and can be carried by cucumber beetles. Plant disease-resistant varieties. Rotate crops. Remove and destroy infected plants.
• Veins in leaves yellow. Spinach blight or spinach yellows is a mycoplasma disease spread by leafhoppers. Remove infected plants. Control leafhopper. Keep the garden free of weeds which can harbor disease.
• Small yellow spots on outer leaves with brown centers enlarge; spot may drop out leaving a ragged hole. Cercospora leaf spot is a fungal disease spread by heavy rainfall and warm temperatures. Keep weeds down in the garden area; they harbor fungal spores. Avoid overhead watering.
• Round water-soaked spots on leaves turn reddish brown to black. Anthracnose is a fungal disease that spreads in high humidity and rainfall. Leaves may wither and fall. Plant may die back. Spray or dust with a fixed copper- or sulfur-based fungicide every 7 to 10 days. Remove and discard infected plants. Avoid working in the garden when it is wet which can result in spread of spores. Keep tools clean.
• Irregular pale green to yellowish to brownish spots on upper leaf surfaces; grayish powder or mold on undersides. Downy mildew is a fungal disease often triggered by wet and humid weather or too frequent overhead irrigation. Improve air circulation. Plant resistant varieties. Rotate crops. Keep garden free of plant debris that can shelter fungus spores.
Spinach Growing Success Tips:
Planting. Spinach is a cool-weather crop that grows best in full sun. Where the weather is very warm, grow spinach in partial shade. Grow spinach in rich, well-drained soil; add aged compost to the planting bed before planting. Spinach will germinate poorly where soil temperatures exceed 75°F. Once seeds germinate and begin to grow, mulch the soil to maintain an even, cool soil temperature.
Planting time. Sow spinach in spring as early as 8 weeks before the average last frost date. For best flavor, spinach should come to harvest before day time temperatures exceed 70°F; increased day length also will cause spinach to flower and set seed. • For a fall crop, sow spinach in late summer 8 weeks before the first expected frost. • For an early spring harvest, sow spinach in fall about 6 weeks before the first expected frost and then protect plants from freezing in winter (plants will grow before the first freezing temperatures then stop and go nearly dormant through the winter). When spring arrives, these plants will complete their growth and be ready for harvest. In mild winter regions, sow spinach every 2 to 3 weeks throughout the fall.
Care. Keep spinach evenly moist and mulch planting beds to keep the soil cool. Protect seedlings from flea beetles, aphids, and leafhoppers with floating row covers. Thin plants to 6 inches apart for best growth and to maintain good air circulation. Keep the garden free of plant debris that can harbor pests.
Harvest. Begin picking spinach leaves when the plant has formed 6 to 8 leaves; harvest the whole plant when leaves are 4 to 6 inches long.
More tips at How to Grow Spinach.