The most frequent issues tomato growers face

Tomato plants fail for a handful of reasons that repeat across almost every garden: too little or too much water, poor light, soil that lacks nutrients, pests, and disease. Most of these problems show up as visible signs on the leaves, stems, or fruit before the plant dies, which means you can catch and fix them if you know what to look for. The good news is that none of these problems requires special equipment—just observation and a willingness to adjust your watering, feeding, or spacing.

The timing matters. Early-season problems (yellowing leaves, slow growth) usually point to water, light, or nutrient issues. Mid-season problems (spots on leaves, wilting despite wet soil) usually point to disease or pests. Late-season problems (fruit not ripening, cracks in the skin) usually point to watering inconsistency or temperature swings. Knowing when the problem started helps you narrow down the cause.

Key Takeaways

  • Tomatoes need consistent moisture—neither waterlogged soil nor bone-dry soil—and the most common mistake is watering the leaves instead of the soil at the base of the plant.
  • Yellowing leaves that start at the bottom of the plant usually mean nitrogen deficiency, while yellowing between the veins usually means magnesium deficiency, and both can be fixed with fertilizer.
  • Blossom end rot (dark, sunken spots on the bottom of the fruit) is caused by inconsistent watering and calcium lockup, not by a lack of calcium in the soil.
  • Fungal diseases like early blight and late blight spread through wet leaves, so watering at soil level in the morning and removing lower leaves prevents most infections.
  • Common pests like hornworms and spider mites are easier to spot and remove by hand early than to treat with sprays once they establish.

Watering problems: too much, too little, or on the wrong part of the plant

Tomatoes need about 1 to 2 inches of water per week, delivered steadily. The soil should feel moist 2 inches down when you push your finger into it, but not soggy. Most home growers either water too often (keeping the soil waterlogged) or water the leaves instead of the soil, which wastes water and invites fungal disease.

If the soil dries out completely between waterings, the plant cannot absorb calcium, which causes blossom end rot—dark, sunken, papery spots on the bottom of the fruit. The fruit is not salvageable once this starts, but you can prevent it on new fruit by watering deeply and consistently. Mulch around the base of the plant (2 to 3 inches of straw or wood chips, kept a few inches away from the stem) helps the soil hold moisture and keeps it from drying out as fast.

Water at the base of the plant in the early morning, before the sun is hot. Wet leaves in the heat of the day can scald, and wet leaves at night invite fungal spores to settle and germinate. A soaker hose or drip line is ideal because it delivers water straight to the soil, but a watering can pointed at the base works too. Avoid overhead sprinklers.

Yellowing leaves and nutrient deficiencies

Tomato leaves turn yellow for different reasons depending on which leaves yellow first and where on the leaf the yellow appears. Nitrogen deficiency shows up as yellowing that starts on the oldest (lowest) leaves and moves upward, while the veins stay green. This is normal late in the season when the plant has used up the nitrogen in the soil, but if it happens early, the soil is depleted. Feed with a balanced fertilizer (like 10-10-10) or a tomato-specific fertilizer every two to three weeks once the plant is flowering.

Magnesium deficiency shows up as yellowing between the veins while the veins themselves stay dark green, usually on the middle leaves first. This is common in acidic soil or when the plant is stressed by inconsistent watering. Dissolve 1 tablespoon of Epsom salt in a gallon of water and spray it on the leaves in the early morning or late evening, or pour it around the base of the plant. Repeat every two weeks until the yellowing stops.

If the entire plant is pale yellow and growth is slow, the soil may lack nitrogen overall. A soil test from your local extension office will tell you what is missing, but in the meantime, side-dress the plant with compost or a balanced fertilizer worked into the top inch of soil around the base.

Spots, blights, and fungal diseases on leaves

Early blight appears as brown spots with concentric rings (like a target) on the lower leaves, usually starting in mid-summer when humidity is high. The spots grow, the leaves yellow and drop, and the disease moves up the plant. Late blight appears as water-soaked spots on leaves and stems, often with a white mold on the underside, and it spreads much faster than early blight, especially in cool, wet weather.

Both diseases spread through water on the leaves and soil splash. Remove the lowest 6 to 12 inches of leaves from the plant (the part most likely to touch soil or splash) once the plant is established. Water only at the base, never overhead. In the morning, remove any leaves that touch the ground or show spots. If the disease is already spreading, remove the entire affected leaf and throw it in the trash (not the compost pile).

Fungal diseases are hard to stop once they take hold, so prevention is the real strategy. Space plants far enough apart that air flows between them (at least 24 inches). Avoid working in the garden when the leaves are wet. If you must treat, sulfur dust or copper fungicide can slow the spread, but neither will stop it completely. Follow the label directions for timing and safety.

Pests: hornworms, spider mites, and whiteflies

Hornworms are large green caterpillars (up to 4 inches long) that eat entire sections of leaves and fruit. They are straightforward to spot because they leave dark droppings on the leaves below them. Check the plant every few days and remove them by hand, dropping them into soapy water. If you see a hornworm with white cocoons on its back, leave it alone—parasitic wasps have laid eggs in it and will hatch to eat other hornworms.

Spider mites are tiny (nearly invisible to the naked eye) and cause leaves to look speckled or stippled, then turn brown and drop. They thrive in hot, dry conditions. Spray the undersides of the leaves with water from a hose to knock them off, or use insecticidal soap if the infestation is heavy. Repeat every three to five days for two weeks.

Whiteflies are small white insects that cluster on the undersides of leaves and fly up when you brush the plant. They weaken the plant by sucking sap and can spread disease. Yellow sticky traps hung near the plant catch many of them. Insecticidal soap or neem oil (applied to the undersides of leaves in the evening) also works, but repeat every five to seven days for at least two weeks.

Fruit problems: cracking, not ripening, and sunscald

Tomatoes crack or split when they absorb water too fast after a dry spell, usually after a heavy rain or a sudden increase in watering. The skin cannot expand as fast as the inside of the fruit grows, so it splits. Prevent this by watering consistently so the soil never dries out completely. Mulch helps. Once a fruit cracks, it is still edible if you use it right away, but it will not store well.

Fruit that stays green at the end of the season may not ripen because the plant is too stressed, the nights are too cold (below 55°F), or the plant is too leafy and shading the fruit. Prune some of the upper leaves in late summer to let light reach the fruit. Stop fertilizing in late summer so the plant focuses energy on ripening rather than growing new leaves. If frost is coming and fruit is still green, pick it and ripen it indoors on a windowsill or in a paper bag with a ripe banana (the ethylene gas speeds ripening).

Sunscald appears as pale, papery patches on the side of the fruit facing the sun, usually in very hot weather. It happens when the fruit is exposed to intense sun without leaf cover. Avoid pruning too many leaves in midsummer heat. If sunscald appears, it does not spread, but the affected area is not pleasant to eat.

Temperature stress and blossom drop

Tomato flowers drop without setting fruit when nighttime temperatures fall below 55°F or daytime temperatures exceed 90°F for several days in a row. This is especially common in spring and early summer when nights are still cool. There is nothing you can do to force the flowers to set once they drop, but the plant will produce new flowers once temperatures stabilize. Be patient—the plant is not dying, it is just waiting for better conditions.

In very hot climates, shade cloth (30 to 50 percent shade) draped over the plant in mid-afternoon can keep the fruit from sunscald and help flowers set. Remove it in the morning so the plant still gets full sun early in the day.

Frequently Asked Questions

Can I save a tomato plant that has lost most of its leaves to disease?

If the plant still has green stems and some leaves at the top, it may recover, especially if you remove all diseased leaves and improve air flow. Stop watering the leaves, water only at the base, and give it two to three weeks. If new growth is green and healthy, the plant is recovering. If the stem turns brown or mushy, the disease has moved into the vascular system and the plant will not recover.

What is the white powder on my tomato leaves?

That is powdery mildew, a fungal disease that looks like someone dusted the leaves with flour. It is less serious than early or late blight, but it still weakens the plant. Remove affected leaves, improve air flow, and spray with sulfur dust or a fungicide labeled for powdery mildew. It thrives in warm, dry conditions, so consistent watering and spacing help prevent it.

Why are my tomatoes small and not very flavorful?

Small, bland fruit usually means the plant is stressed by inconsistent watering, poor light (less than six to eight hours of direct sun), or overcrowding. It can also mean the soil is depleted of nutrients. Move the plant to a sunnier spot if possible, water consistently, and feed with a balanced fertilizer every two to three weeks once flowering starts. Thin out nearby plants to improve air flow.

Should I prune the suckers that grow between the main stem and branches?

Pruning suckers (called "determinate" pruning) on indeterminate varieties (the tall, vining types) directs energy into fruit production and improves air flow. On determinate varieties (the bushy, compact types), pruning is not necessary and can reduce yield. If you do prune, do it in the morning when the plant is turgid, and use clean scissors to avoid spreading disease.

Can I grow tomatoes in a pot, and what size do I need?

Yes, tomatoes grow well in pots as long as the pot is large enough. A 5-gallon bucket is the minimum for a determinate variety, and a 10-gallon pot or larger is better for indeterminate varieties. Use potting soil (not garden soil), water more often than in-ground plants because pots dry out faster, and feed every two weeks with a balanced fertilizer once flowering starts.