Why Tomato Leaves Turn Yellow

The position and pattern of yellow tomato leaves help separate normal aging from moisture, root, light, or nutrition problems.

Position on the plant is the first clue

A few older leaves at the very bottom turning yellow and dropping is normal ageing, particularly once the plant is carrying fruit. Yellowing that spreads widely, or that appears on new growth at the top, is worth investigating. Where it starts narrows the possibilities faster than the colour itself does.

Check moisture and drainage before anything else

The most common driver is the root zone — mix that stays wet, poor drainage, or repeated severe drying. Waterlogged roots cannot take up nutrients even when nutrients are present, which produces yellowing that looks like a feeding problem and will not respond to feeding. Feel below the surface and check the holes are clear.

Then check pot size and light

A tomato in an undersized container dries out daily, and the resulting stress shows in the foliage. Below six hours of direct sun a tomato also yellows and thins as it fails to support its own leaf area. Both look like deficiencies and neither is fixed by fertiliser.

When feeding is genuinely the answer

If light is adequate, the container is a reasonable size, watering is steady, drainage works, and the plant has been in the same mix for months, then depletion is plausible. Use a product labelled for edibles, measure the dilution exactly, and never feed a waterlogged or bone-dry root zone.

Do not expect the yellow leaves to recover

Once a leaf has yellowed it will not turn green again. Correct the strongest condition you found and judge the plant on the leaves it produces next. If new growth comes in healthy and green, the change worked, even though the old foliage still looks poor.

When to look further

Yellowing between the veins on new growth, sudden one-sided wilting with yellowing, or spots and lesions alongside the colour change point beyond routine care. Photograph the newest growth and seek local horticultural advice before applying any treatment, particularly on a crop you intend to eat.