Yellow leaves usually mean one of four things: too much or too little water, a nutrient shortage, disease, or pests

Tomato leaves turn yellow because the plant is either stressed by its environment, missing something it needs to make chlorophyll (the pigment that keeps leaves green), or fighting off disease or insects. The good news is that the cause is almost always visible if you look at the pattern of yellowing and check the soil and undersides of the leaves. Most yellow-leaf problems can be reversed if you catch them early.

The location of the yellow leaves matters. If only the lowest, oldest leaves are turning yellow and dropping off, that is often normal as the plant grows and redirects energy upward. If yellowing spreads from the bottom up, or if new growth at the top is yellow, or if the whole plant is fading, something is wrong with water, nutrients, or disease.

Key Takeaways

  • Overwatering is the most common cause of yellow tomato leaves; soil should dry out slightly between waterings, and the pot must have drainage holes.
  • Nitrogen deficiency shows as yellowing between the leaf veins while veins stay green, and is fixed by feeding with a balanced fertilizer or compost tea.
  • Early blight and septoria leaf spot are fungal diseases that start on lower leaves and move upward; remove affected leaves and improve air circulation around the plant.
  • Spider mites and whiteflies live on the undersides of leaves and cause yellowing with tiny webs or sticky residue; spray the undersides with water or insecticidal soap.

Overwatering and poor drainage cause the most yellow leaves

Tomatoes need water, but their roots rot if they sit in wet soil. When roots cannot absorb oxygen, they cannot take up nutrients or water properly, and the plant shuts down leaf color as a sign of stress. The leaves turn yellow all over the plant, often starting with a dull, pale look before turning bright yellow.

Check the soil by pushing your finger two inches down. If it feels soggy or smells sour, you are watering too often. Tomato soil should feel moist but not wet—like a wrung-out sponge. In hot weather, outdoor tomatoes may need water every day or two, but in cool weather or indoors, once or twice a week is usually enough. Always use a pot with drainage holes at the bottom. If water sits in the saucer under the pot for more than an hour after watering, empty it.

If you have been overwatering, stop for a few days and let the soil dry out slightly. Remove any yellow leaves that are touching the soil, because they can trap moisture and encourage fungal disease. New growth should return to green within a week or two if the roots are not permanently damaged.

Underwatering stresses the plant and turns leaves yellow and papery

The opposite problem—not enough water—also causes yellowing, but it looks and feels different. Underwatered tomato leaves turn yellow and then papery or crispy, and the whole plant looks droopy even right after you water it. The soil pulls away from the sides of the pot and becomes hard to wet.

If the soil is bone-dry and pulls away from the pot edges, soak the whole pot in a bucket of water for 10 to 15 minutes so the soil can absorb water evenly. Then water normally. Outdoor tomatoes in full sun during summer heat may need water every single day, especially in containers. Stick your finger into the soil each morning—if the top inch is dry, water deeply until it drains from the bottom.

Nitrogen deficiency shows as yellowing between the veins

When a tomato plant runs low on nitrogen, the older leaves (at the bottom) turn yellow first, but the veins stay green. This creates a pattern that looks like a green net on a yellow leaf. New leaves at the top stay green longer. The plant grows slowly and produces fewer flowers.

Nitrogen is the nutrient plants use most, and it washes out of soil with watering over time. If you planted in potting soil without added fertilizer, or if you have been growing tomatoes in the same soil for months, nitrogen is likely depleted. Feed with a balanced fertilizer (like 10-10-10 or 5-5-5) every two to three weeks, or use compost tea or fish emulsion weekly. Follow the label directions—too much fertilizer can burn roots and make yellowing worse.

You should see new green growth within a week or two of feeding. If yellowing continues to spread and new leaves are also pale, the problem may be something else, or the roots may be too damaged to absorb nutrients.

Early blight and septoria leaf spot are fungal diseases that spread upward

Two common fungal diseases turn tomato leaves yellow and then brown with dark spots or rings. Early blight starts on the lowest leaves with brown spots that have a target-like ring pattern, and the leaf turns yellow around the spot before dropping off. Septoria leaf spot shows as small circular spots with dark borders and gray centers, also starting at the bottom and moving up.

Both diseases spread in warm, humid conditions, especially when leaves stay wet. Water at the soil level in the morning, not from above, so leaves dry quickly. Remove any yellow or spotted leaves as soon as you see them—cut them off with clean scissors and throw them away (not in compost). Improve air circulation by spacing plants farther apart and pruning lower branches so air flows around the base.

If disease is severe, spray the plant with a fungicide labeled for tomatoes, following the label directions. Copper fungicides and sulfur are common choices for home gardeners. Spray every 7 to 10 days until the disease stops spreading. Do not spray in temperatures above 85°F or in direct sun, as this can burn leaves.

Spider mites and whiteflies cause yellowing with visible damage on leaf undersides

Tiny pests that live on the undersides of leaves can turn them yellow by sucking out the plant's juices. Spider mites create fine webs on the undersides and cause yellowing with tiny pale dots. Whiteflies are small white insects that cluster on the undersides and leave sticky residue (called honeydew) that turns black with mold.

Check the undersides of yellow leaves with a magnifying glass or by holding a leaf up to the light. If you see tiny moving dots, webs, or white insects, you have pests. Spray the undersides of all leaves thoroughly with a strong stream of water from the hose to knock off the pests. Repeat every few days for two weeks. If pests return, spray with insecticidal soap, following the label directions and coating the undersides well.

Magnesium and other nutrient shortages cause specific yellowing patterns

Besides nitrogen, tomatoes need magnesium, potassium, iron, and other nutrients. Magnesium deficiency shows as yellowing between the veins on older leaves while the veins stay green—similar to nitrogen deficiency, but it usually starts on the sides of the leaf rather than all over. Iron deficiency causes yellowing on new leaves at the top while veins stay green.

If you suspect a nutrient shortage other than nitrogen, a soil test from your local extension office can tell you exactly what is missing. In the meantime, spray the leaves with a diluted liquid fertilizer (called foliar feeding) so the plant can absorb nutrients through the leaves. This gives faster relief than feeding the soil, though it is not a permanent fix. Epsom salt dissolved in water (one tablespoon per gallon) can help with magnesium deficiency.

Frequently Asked Questions

Should I remove yellow leaves from my tomato plant?

Yes, remove yellow leaves that are touching soil or are heavily spotted with disease. Healthy yellow leaves higher up on the plant can stay if they are not diseased. Removing lower leaves also improves air circulation and reduces disease risk. Use clean scissors and throw the leaves away rather than composting them, especially if disease is present.

Can yellow tomato leaves turn green again?

Once a leaf is fully yellow, it will not turn green again. However, new growth at the top of the plant will be green and healthy if you fix the underlying problem—whether that is watering, feeding, disease, or pests. The plant redirects energy to new leaves, so the old yellow ones eventually drop off naturally.

What is the best fertilizer for yellowing tomato plants?

A balanced fertilizer with equal parts nitrogen, phosphorus, and potassium (like 10-10-10) works for most nutrient shortages. Fish emulsion, compost tea, and seaweed extract are also good choices. If you suspect only nitrogen is low, a higher-nitrogen fertilizer (like 20-10-10) works faster. Always follow label directions and do not overfeed, as excess fertilizer can damage roots.

How do I prevent yellow leaves on tomatoes?

Water at the soil level in the morning so leaves dry quickly, use well-draining soil with drainage holes, feed every two to three weeks during the growing season, space plants for good air circulation, and remove lower leaves as the plant grows. These steps prevent most yellowing from water stress, nutrient shortage, and disease.

Is it normal for the bottom leaves of tomato plants to turn yellow?

Yes, it is normal for the oldest leaves at the very bottom to yellow and drop as the plant grows and redirects energy upward. However, if yellowing spreads quickly up the plant, or if many leaves are affected at once, something is wrong. Watch the pattern—slow, gradual loss of the lowest leaves is fine; rapid yellowing across the plant is a sign to investigate.