Tomato Plants Turning Yellow: 7 Causes & Fixes

If your tomato plants are turning yellow, the most common causes are nutrient deficiencies (especially nitrogen), improper watering, diseases like early blight, or pest infestations. Immediate action can often save your plants—check soil moisture first, then examine leaf patterns to identify specific nutrient needs or disease symptoms before applying targeted solutions.

Discovering yellow leaves on your tomato plants can trigger gardening panic, but most causes are treatable with the right approach. As a seasoned gardener who's rescued countless yellowing tomato crops, I've identified seven primary culprits and their solutions. This guide delivers actionable steps you can implement today to revive your plants and prevent future issues—no horticulture degree required.

Immediate Assessment: What to Check Right Now

When you notice yellowing tomato leaves, your first 24 hours determine whether your plants recover. Start with these critical checks before jumping to conclusions:

Yellowing Pattern	Most Likely Cause	Urgency Level
Lower leaves turning yellow first	Nitrogen deficiency	Moderate
Young leaves yellow with green veins	Iron deficiency	High
Yellow patches with dark centers	Early blight	Critical
Entire plant yellowing rapidly	Overwatering	Emergency

This visual diagnostic chart from the University of California Agriculture and Natural Resources helps pinpoint problems based on yellowing patterns. Most tomato growers (78% according to Cornell University Cooperative Extension surveys) initially misdiagnose the cause, wasting precious time on ineffective treatments.

Nutrient Deficiencies: The Silent Plant Killer

Nutrient issues cause nearly 60% of yellowing tomato cases. Each deficiency creates distinct yellowing patterns that reveal exactly what your plants need:

Nitrogen Deficiency

When older leaves turn uniformly yellow while new growth remains green, your plants need nitrogen. This mobile nutrient moves from older to newer leaves during shortages. Correct this by:

• Applying balanced organic fertilizer (4-4-4) at half-strength
• Incorporating blood meal (12% nitrogen) into soil
• Adding compost tea weekly until color improves

Iron Chlorosis

Young leaves yellowing with persistent green veins indicates iron deficiency, common in alkaline soils. The USDA notes this affects 30% of home garden tomatoes in western states. Fix it by:

• Lowering soil pH to 6.0-6.5 with elemental sulfur
• Applying chelated iron foliar spray (follow package directions)
• Avoiding over-fertilization with phosphorus which blocks iron uptake

Watering Woes: The Goldilocks Principle

Tomato plants need consistent moisture—not too wet, not too dry. The Cornell University Vegetable Program confirms improper watering causes 25% of yellowing cases. Follow these guidelines:

Overwatering Signs

• Yellowing starts at leaf tips and spreads inward
• Soil remains soggy 24 hours after watering
• Roots appear brown and mushy

Underwatering Symptoms

• Leaves turn pale yellow overall
• Soil pulls away from container edges
• Plants wilt by midday despite moist soil surface

Implement the finger test: insert your finger 2 inches into soil. Water only when dry at that depth. During fruiting, tomatoes need 1-2 inches of water weekly, preferably delivered at the base through drip irrigation.

Disease Diagnosis: When Yellow Means Danger

Several diseases cause yellowing with distinctive patterns. Early identification prevents garden-wide outbreaks:

Early Blight (Alternaria solani)

This fungal disease creates target-like spots with yellow halos. The American Phytopathological Society reports it affects 40% of home tomato gardens annually. Combat it by:

• Removing affected leaves immediately
• Applying copper fungicide every 7-10 days
• Watering at soil level to prevent splash transmission

Verticillium Wilt

Yellow V-shaped patterns starting at leaf edges indicate this soil-borne fungus. Unlike nutrient issues, yellowing appears first on one side of the plant. Unfortunately, no cure exists—remove infected plants and solarize soil before replanting.

Pest Problems: Tiny Troublemakers

Several pests cause yellow stippling or mottling:

• Spider mites: Fine webbing on undersides with bronze-yellow stippling
• Aphids: Curled, yellowing leaves with sticky honeydew residue
• Whiteflies: Clouds of tiny insects when disturbed with yellowing leaves

For immediate pest control, spray plants thoroughly with insecticidal soap, focusing on leaf undersides. Introduce beneficial insects like ladybugs for ongoing protection.

Environmental Stress: Beyond Your Control

Yellowing isn't always your fault. These environmental factors cause temporary issues:

• Temperature extremes: Below 50°F or above 90°F stresses plants
• Sunscald: Sudden exposure to intense sun after cloudy periods
• Natural senescence: Lower leaves yellow as plants mature (normal process)

Remember that some yellowing is normal—tomato plants naturally shed older leaves as they grow. The University of Minnesota Extension confirms that losing 1-2 bottom leaves weekly is healthy plant development, not a problem requiring intervention.

Prevention Plan: Keep Tomatoes Green All Season

Proactive care prevents 80% of yellowing issues. Implement these strategies from planting through harvest:

• Test soil before planting (ideal pH: 6.2-6.8)
• Use balanced organic fertilizer every 3-4 weeks
• Mulch with straw to maintain consistent soil moisture
• Rotate crops annually to prevent soil-borne diseases
• Choose disease-resistant varieties (look for VFN on labels)

When yellowing appears, follow this decision timeline: Day 1—assess pattern and moisture; Day 2—test soil nutrients; Day 3—apply targeted treatment; Day 7—evaluate improvement. Most issues show visible improvement within 7-10 days of proper treatment.

Can yellow tomato leaves turn green again?

Once leaves turn yellow from nutrient deficiency or disease, they won't return to green. However, proper treatment prevents further yellowing and promotes healthy new growth. Remove severely affected leaves to redirect plant energy to recovery.

How often should I water tomato plants to prevent yellowing?

Water deeply 1-2 times weekly, providing 1-2 inches of water. Container plants may need daily watering during hot weather. Always check soil moisture 2 inches down before watering—only water when dry at that depth. Consistent moisture prevents both over and underwatering issues.

Is Epsom salt good for yellowing tomato plants?

Epsom salt helps only if magnesium deficiency causes the yellowing (yellowing between veins on older leaves). Apply 1 tablespoon per gallon of water as a foliar spray. It won't help with nitrogen deficiency, diseases, or other common causes of yellowing.

Should I remove yellow leaves from tomato plants?

Remove severely yellowed or diseased leaves to prevent energy drain and disease spread, but don't over-prune. Keep leaves with partial yellowing that still have green tissue. Always sterilize pruners between cuts when removing diseased foliage to prevent spreading pathogens.