Bottom leaves of tomato plant turning yellow?

A few oldest lower tomato leaves can yellow normally as the plant matures, but yellowing that spreads usually means stress from water, nutrients, weather, leaf disease, or spray damage.

Answer what you can see

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Push a finger two inches into the soil. What does it feel like?

Which leaves are affected?

What has the weather been doing?

How fast did this happen?

Dry-soil stress and low nitrogen can both start on the oldest lower leaves slowly, and waterlogged soil, low nitrogen, and Early blight or Septoria can overlap after heavy rain; check soil moisture first, then look for leaf spots and whether the yellowing is even or blotchy.

The causes in full

Dry-soil water stressMOST COMMON

How to tell
Check for soil that is dry, crumbly, or baked 2 inches down, plus lower leaves yellowing and the plant wilting hardest in the afternoon.

What to do
Water deeply now if the soil is dry 2 inches down, soaking the bed slowly so water reaches the roots instead of running off. Loosen only the crusted soil surface, then add mulch to slow drying.

Waterlogged soil after rainCOMMON

How to tell
The soil feels wet or swampy 2 inches down, yellowing is low on the plant or all over, and the problem started after storms or soil stayed wet for days.

What to do
Stop irrigating and pull mulch back for a few days; do not water again until the soil is dry 2 inches down. If water stands after rain, make shallow channels to move runoff away from the tomato row and improve the bed with compost between seasons.

Low nitrogen or depleted soilCOMMON

How to tell
The oldest lower leaves turn evenly pale yellow first, the newer leaves look greener, and there are no spots, chewing, or one-sided scorch marks.

What to do
Side-dress with a tomato fertilizer or finished compost; if the soil is dry 2 inches down, water it in deeply. Do not keep adding water to damp soil just because the leaves are yellow.

Heat and afternoon sun scorchCOMMON

How to tell
Yellow or pale, papery patches are worst on the side facing the hottest afternoon sun, especially after scorching days, while shaded leaves look better.

What to do
Put up temporary 30–40% shade cloth during extreme afternoon heat and keep mulch over the root zone. Water deeply only if the soil is dry 2 inches down.

Early blight or Septoria leaf spot diseaseCOMMON

How to tell
Look closely at the lower yellow leaves for many small brown or tan spots, often with yellow halos, especially after wet weather or splashing soil.

What to do
Clip off the worst spotted lower leaves and put them in the trash, then mulch under the plant to stop soil splash. Water at soil level only when the soil is dry 2 inches down, and use a labeled tomato fungicide if new spotted leaves keep appearing.

Herbicide drift, fertilizer burn, or cold shockLESS COMMON

How to tell
The newest tip growth yellows, twists, or looks narrow after a cold night, nearby weed-killer use, fertilizer spray, or granules landing on leaves; damage may hit one exposed side more than the rest.

What to do
For cold, cover plants on the next cold night; for spray drift, prevent any more exposure; for fertilizer granules, brush them off leaves and the soil surface. Do not fertilize again or add extra water unless the soil is dry 2 inches down, then watch whether new growth comes in normal.

Will it recover?

Yellow tomato leaves usually do not turn green again; the goal is to stop the spread and get healthy new green growth.

Stopping it happening again

Grow tomatoes in full sun, mulch the bed, feed steadily, keep leaves as dry as practical, rotate planting spots, and water deeply only when the soil is dry 2 inches down.