Gardening tips: ‘Most common’ cause of tomato leaves turning yellow – how to solve

Growing tomatoes yourself is well worthwhile because the taste of a homegrown tomato is far superior to a store-bought version, so seeing the leaves of your carefully tended plants turn yellow can be alarming. There are actually a few reasons that mean your garden ideas can be compromised by tomato leaves turning yellow. Fortunately, gardening experts have shared the “most common” reason for this and how it can be resolved.

The good news about tomato leaves turning yellow is that many of the problems that cause the colour change can be remedied. 

Be mindful that, as a rule, yellowing leaves should be removed when pruning tomato plants and discover the details about why leaves go yellow below.

Issues with watering can cause tomato leaves to turn yellow – and both under and overwatering could be the cause.

Soil that is too wet suffocates the roots, which rot, and the plant misses out on both water and nutrients.

Matt Eddleston, founder of Gardening Vibe explained: “Overwatering is one of the most common causes of yellowing tomato leaves.

“Look for signs of the plant wilting, bumps on the lower leaves, and cracked fruit as confirmatory signals.

READ MORE: Gardening tips: ‘Best time of day’ to water your garden plants

“And check that the pot has adequate drainage holes.”

If underwatering is the problem instead, tomato leaves will likely wilt first then turn yellow.

Soil compaction is another reason tomato leaves turn yellow.

Silvia Borges, owner of EnviroMom said: “Having compact soil around your tomato will suffocate it and it will go yellow from the bottom up.”

Instead she recommends loosening the soil around the plant.

Be aware, though, that it is possible to damage the roots with this remedial action, so prepare soil well before planting tomatoes to swerve the issue further down the road.

Tomato leaves could turn yellow because the plant is short on nutrients, including nitrogen, iron and magnesium. 

Tomatoes should be fed regularly using a tomato fertiliser to avoid nitrogen deficiency that can cause leaves to turn yellow, and which you’ll see happening to older leaves first. 

A lack of iron also causes yellowing, especially in younger leaves, while magnesium deficiency can result in yellow areas between the veins on older leaves.

Another reason why your tomato leaves are turning yellow is disease.

Matt explained: “Fungal and viral diseases are common explanations for yellow tomato leaves.

“Early blight is a fungal disease that usually appears after the plant starts to produce fruit and causes brown, circular spots with the surrounding leaf turning yellow.”

Late tomato blight can also turn leaves musty yellow, and tomato blight treatments should be carried out.

Matt continued: “Some locations are more susceptible to fungal disease because of heat and humidity.

“If you find yourself having a problem with fungal diseases, you can spray your plants with an organic fungicide.

“A common viral disease that causes leaf yellowing is the tomato yellow leaf curl virus. 

“The margins of the leaves turn yellow, starting with the newer leaves. 

“The leaves curl over at the edges and often have stunted growth. 

“The virus is spread between plants by the silverleaf whitefly. Infected plants have to be removed and carefully disposed of.”

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