Tomato Leaves Turning Yellow

Why are my tomato leaves turning yellow?

Yellow tomato leaves are not a single problem — they are a symptom with seven distinct causes, each identified by the pattern, location, and progression of the yellowing. Treating the wrong cause wastes time and can make the problem worse.

Start by answering three questions:

1. Where on the plant is the yellowing? Bottom leaves, middle of the plant, or new top growth?
2. What does the yellowing look like? Uniform pale yellow, yellow with dark spots, mottled yellow-green, or yellow between the veins only?
3. What are the conditions? Has the plant been overwatered? Has it not been fertilized? Is it late in the season?

The table below maps these patterns to causes so you can identify the problem before treating it.

Diagnosis by yellowing pattern

Work down this list before purchasing any product. Applying a nitrogen fertilizer to a plant with root rot makes the problem worse. Applying copper fungicide to a plant with nitrogen deficiency does nothing.

1. Nitrogen deficiency

Nitrogen deficiency is the most common cause of yellow tomato leaves in US home gardens. Nitrogen is mobile in the plant — when the plant lacks nitrogen, it pulls it from older leaves first and redirects it to new growth. This creates a characteristic pattern: yellowing starts at the lowest, oldest leaves and moves upward.

What it looks like:

• Uniform pale yellow, starting at the leaf tip and spreading across the whole leaf
• No spots, no mottling, no lesions — just pale, washed-out color
• New growth at the top of the plant is still green and healthy
• Affected leaves eventually drop

Causes in US gardens:

• Heavy rainfall leaching nitrogen from soil (common in humid eastern US, Zone 5–8)
• Sandy soils that don’t hold nitrogen between applications
• No fertilization after transplanting
• Rapid early growth that depleted soil nitrogen faster than expected

Fix: Apply a nitrogen-containing fertilizer. Options from fastest to slowest acting:

1. Liquid fish emulsion (5-1-1 or similar): drench around the base; results visible in 5–7 days
2. Liquid tomato fertilizer (balanced or high-N): similar timeline
3. Granular fertilizer worked into the top inch of soil: 2–3 weeks to full effect

Do not over-apply nitrogen after fruit set begins. Excess nitrogen causes excessive foliage at the expense of fruit production. Apply once at recommended rates, then re-evaluate in two weeks.

See tomato fertilizer for a full guide to nitrogen timing and formulations across the growing season.

2. Early blight (Alternaria solani)

Early blight is the most common fungal disease of tomatoes in the US, affecting gardens across Zones 4–10. It starts on the lowest leaves and moves upward as the season progresses.

What it looks like:

• Dark brown or black spots appear first — irregular in shape, often with a yellow halo around them
• As spots enlarge, the surrounding leaf tissue turns yellow
• Spots may show concentric rings (the characteristic “target” pattern of Alternaria)
• Affected leaves yellow completely and drop
• Progresses upward through the plant by late summer

How to distinguish it from nitrogen deficiency: Early blight always shows spots before yellowing. Nitrogen deficiency is uniform yellow with no spots. If you see spots, it is not nitrogen deficiency.

Fix:

• Remove all affected lower leaves immediately. Dispose of them in the trash — not the compost pile, where spores can overwinter.
• Apply copper fungicide (copper hydroxide or copper octanoate) to remaining leaves and new growth. Copper does not cure infected tissue but prevents the spread to healthy leaves.
• Water at the soil line, not overhead. Blight spreads through water splash from soil to leaves.
• Mulch around the base of the plant to prevent soil splash.

See early blight tomatoes for full treatment protocol including spray intervals and resistant variety selection.

3. Septoria leaf spot

Septoria leaf spot (Septoria lycopersici) is sometimes confused with early blight but has a distinct appearance. It is a significant problem in humid eastern US gardens from Zone 5 eastward.

What it looks like:

• Small, circular spots (1/8 to 1/4 inch diameter) with dark brown borders and lighter gray or tan centers
• Tiny dark dots may be visible in the center of spots — these are the spore bodies (pycnidia)
• Spots do not have the yellow halo typical of early blight, but heavy infection causes the whole leaf to yellow and drop
• Begins on lower leaves and moves upward

How to distinguish it from early blight: Septoria spots are small and circular with dark borders. Early blight spots are larger, irregular, and have the concentric ring pattern. Both start at the bottom of the plant.

Fix: The treatment is the same as for early blight: remove affected leaves, apply copper fungicide, water at soil level, and mulch to prevent soil splash. Start treatment as soon as the first spots appear — septoria spreads quickly once established. In warm, humid conditions (Zone 6–8 east of the Rockies), a weekly copper spray schedule during July and August prevents septoria from defoliating the plant before fruit ripens.

4. Magnesium deficiency

Magnesium deficiency causes a distinct yellowing pattern called interveinal chlorosis — the leaf tissue between the veins turns yellow while the veins themselves remain green. Unlike nitrogen deficiency, magnesium deficiency appears on older, middle-age leaves rather than the newest growth.

What it looks like:

• Yellow patches between the green veins of middle-aged leaves
• Veins stay distinctly green, creating a prominent pattern
• New leaves at the top of the plant are green
• Does not have spots or lesions

Causes in US gardens:

• Sandy, acidic soils in the Southeast (Zones 7–9) are prone to magnesium deficiency
• High potassium or calcium in the soil can block magnesium uptake even when magnesium is present
• Long growing seasons without fertilization deplete soil magnesium

Fix: Epsom salt (magnesium sulfate) is the standard home remedy and genuinely works for magnesium deficiency. Mix 1 tablespoon of Epsom salt per gallon of water and drench around the base of the plant. You can also apply as a foliar spray at 1 tablespoon per gallon of water, sprayed directly on affected leaves. Repeat every 2 weeks until new growth is green.

Confirm magnesium deficiency with a soil test before applying Epsom salt. If the soil has sufficient magnesium, excess application does nothing and can create other imbalances.

5. Iron or manganese deficiency

Iron and manganese deficiency both cause interveinal chlorosis, but on new growth at the top of the plant rather than older leaves. This is the key distinction from magnesium deficiency.

What it looks like:

• New leaves (youngest growth) are pale yellow between the veins
• Veins remain green
• Old leaves look normal or only mildly affected
• In severe cases, entire new leaves turn pale yellow-white

Iron vs. manganese: Iron and manganese deficiencies look nearly identical. Both affect new growth and both show interveinal chlorosis. The distinction requires a soil test. In practice, the fix is similar for both.

Causes in US gardens: Iron and manganese become unavailable to plants when soil pH is too high (above 7.0–7.5). Even if iron and manganese are present in the soil, roots cannot absorb them at high pH. This is more common in western US gardens (Zones 8–10 in California, Arizona, New Mexico) where soils naturally trend alkaline.

Fix:

1. Test soil pH. If pH is above 7.0, adjust with soil sulfur or acidifying fertilizer. Lowering pH makes iron and manganese available again.
2. Apply chelated iron as a foliar spray or soil drench. Chelated iron remains available across a wider pH range than standard iron sulfate.
3. Do not apply lime or wood ash near tomatoes in alkaline soils — these raise pH further.

See tomato fertilizer for the role of soil pH in nutrient availability.

6. Mosaic virus (CMV or TMV)

Cucumber mosaic virus (CMV) and tobacco mosaic virus (TMV) both infect tomatoes and produce a characteristic mottled yellowing that is distinct from any nutrient deficiency or fungal disease.

What it looks like:

• Irregular yellow-green mottling or mosaic pattern on leaves — patches of yellow mixed with normal green, often appearing distorted
• Leaves may be smaller than normal, curled, or twisted
• New growth is often most severely affected
• In severe cases, the entire plant appears stunted

How to distinguish it from other causes: Mosaic virus creates mottling — irregular mixed yellow-green — not uniform yellowing or distinct spots. The pattern looks almost marbled. Additionally, CMV-infected plants may show other symptoms: distorted fruit, reduced size, and stunted overall growth.

Important: There is no cure for viral infection in tomatoes. Once a plant is infected, the virus spreads through the plant systemically and cannot be eliminated. The plant continues to serve as a virus reservoir that aphids spread to other plants.

What to do:

• Remove infected plants entirely. Do not compost them.
• Control aphid populations on remaining healthy plants — aphids are the primary vector for CMV.
• Wash hands and tools with soap and water after handling infected plants. TMV can spread through contact.
• In future seasons, do not co-plant cucumbers and tomatoes in beds where CMV was present the previous year.

See can you plant tomatoes and cucumbers together for more on CMV risk in shared beds.

7. Overwatering and root problems

Overwatering causes yellowing by starving roots of oxygen. Waterlogged soil drives oxygen out, and roots that cannot breathe cannot absorb nutrients — even if nutrients are present in the soil.

What it looks like:

• Uniform pale yellowing, often on multiple leaves at once rather than moving from bottom to top
• Leaves may wilt during the day despite wet soil
• Soil stays wet 48–72 hours after watering
• In severe cases, roots appear brown and mushy when you dig carefully at the base

Root rot: Extended overwatering leads to Phytophthora or Pythium root rot. Affected roots turn brown, mushy, and foul-smelling. A plant with significant root rot will not recover.

Fix:

• Stop watering and allow the soil to dry out between sessions
• If water pools around the plant for more than a day, the bed needs drainage improvement — add compost to improve soil structure, or build a raised planting mound
• Tomatoes in containers should have drainage holes that are not blocked
• In heavy clay soils (common in eastern Zone 5–7), raised beds with amended soil prevent most overwatering problems

See how often should you water tomato plants for zone-specific watering frequency guidelines.

Seasonal yellowing: when it’s normal

Some yellowing in tomato plants is not a problem — it is normal plant behavior.

Lower leaf senescence in late season: As tomato plants age and fruits mature, the plant pulls energy from lower, older leaves and redirects it to fruit development. Yellowing of the bottom 8–12 leaves from August onward in Zone 5–7 is normal and does not require treatment.

First leaves (cotyledons): The first two seed leaves (cotyledons) that emerged from the seed often yellow and drop within the first 3–4 weeks after germination. This is normal — the true leaves have taken over photosynthesis.

Heavily shaded leaves: Leaves deep inside a dense tomato canopy that receive no direct light eventually yellow and drop. The plant stops investing resources in leaves that contribute no photosynthesis. This is normal and can be managed by pruning interior leaves for better airflow.

The distinction from problematic yellowing: normal senescent yellowing is slow, confined to the oldest leaves, and does not spread rapidly up the plant. Problematic yellowing progresses over days, not weeks, and moves upward through the plant.

Treating yellow tomato leaves: step by step

When you find yellowing leaves on your tomatoes, work through this sequence:

Step 1: Identify the location.

• Bottom leaves: nitrogen deficiency, early blight, or septoria
• Middle leaves: magnesium deficiency or early blight
• Top new growth: iron, manganese, or rare severe nitrogen deficiency
• All over: mosaic virus or overwatering

Step 2: Look for spots. Any spots means a fungal disease or virus, not a nutrient deficiency. No spots points toward deficiency or watering issues.

Step 3: Check watering. If the soil has been consistently wet, check drainage before applying fertilizer.

Step 4: Apply the right treatment.

Step 5: Monitor for 2 weeks. If the treatment is correct, yellowing should stop progressing within 1–2 weeks. If it continues, reconsider your diagnosis.

Preventing yellow leaves next season

Most causes of yellow tomato leaves are preventable with four practices:

1. Start with a soil test. A soil test before the season identifies pH issues, magnesium deficiency, and nitrogen levels before they cause problems. Most state Cooperative Extension services offer soil tests for $15–25. Results include amendment recommendations specific to your soil.

2. Mulch consistently. A 2–3-inch layer of straw or wood chip mulch prevents soil splash that spreads early blight and septoria. It also moderates soil moisture, reducing the overwatering and drought cycles that impair nutrient uptake.

3. Water at the soil line. Overhead irrigation keeps leaves wet, extending the window for fungal infection. Drip irrigation or soaker hose eliminates overhead moisture and reduces disease pressure significantly in humid climates. See how often should you water tomato plants for timing recommendations.

4. Choose resistant varieties. Many modern tomato varieties carry resistance codes to early blight (A) and verticillium/fusarium wilt (V, F). Choosing resistant varieties does not eliminate disease but reduces pressure and extends the productive season. See how to grow tomatoes for variety recommendations by zone.

For a broader look at common tomato problems beyond yellowing — blossom drop, blossom end rot, cracking, and sunscald — see blossom end rot for one of the most frequently misdiagnosed tomato problems in US home gardens.

The USDA National Institute of Food and Agriculture funds Cooperative Extension programs in every US state. Your state’s Extension plant disease clinic can confirm disease diagnoses from leaf samples — a useful step when you can’t identify a yellowing pattern from visual description alone.