Bottom leaves of tomato plant turning yellow?

Tomato leaves turning yellow usually points to water stress, rain-related root or leaf disease, or nutrient shortage, though one or two oldest lower leaves yellowing as the plant grows can be normal.

Answer what you can see

The ranking updates as you go. Nothing is sent anywhere.

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?

Some answers overlap: waterlogged roots and early blight or Septoria can both follow heavy rain with yellow lower leaves, and dry heat stress and chemical burn can both show up fast on sun-facing leaves; spots, recent sprays or fertilizer, and the actual soil feel are the tie-breakers.

The causes in full

Dry soil and heat stressMOST COMMON

How to tell
The soil is dry and crumbly 2 inches down or baked hard and cracked, the plant may wilt in the hot part of the day, and yellowing is worst on lower leaves or the side hit by strong afternoon sun.

What to do
If the soil is dry and crumbly 2 inches down or baked hard and cracked, water slowly and deeply at the base until the root zone is moist. Add mulch, and during a heatwave use temporary afternoon shade cloth rather than moving the plant out of full sun.

Waterlogged roots after heavy rainCOMMON

How to tell
The soil is waterlogged or still damp 2 inches down days after rain, lower leaves yellow evenly, and the plant may look wilted even though the ground is wet.

What to do
If the soil is waterlogged, do not irrigate again until the soil is dry and crumbly 2 inches down. Pull mulch back for a few days, make shallow drainage channels if water is standing, and improve the bed with compost after the season.

Early blight or Septoria leaf spotCOMMON

How to tell
Look closely at the yellow lower leaves: this is likely if they have many small brown, tan, or dark spots, often after wet weather or splashy watering.

What to do
Remove the worst spotted lower leaves when the plant is dry and throw them away. Keep leaves off the soil, mulch under the plant, improve airflow with staking, and water only at the base when the soil is dry and crumbly 2 inches down.

Nutrient shortage or normal lower-leaf agingCOMMON

How to tell
If only one or two oldest lower leaves are yellow while the rest of the plant is growing well, it can be normal aging; if many older leaves fade from the bottom up, or new growth is pale, suspect a nutrient problem.

What to do
If it is only a couple of old lower leaves, clip them off and keep watching. If many leaves are fading and the plant has not been fed, apply a tomato fertilizer or compost according to the label; if the soil is dry and crumbly 2 inches down, water first, and water granular fertilizer in thoroughly after applying it to moist soil.

Cold injury or late frostLESS COMMON

How to tell
Yellow, pale, or whitish patches appeared right after a cold snap, especially on exposed top leaves or tender new growth.

What to do
Do not prune right away unless tissue is clearly dead; wait for new growth, then trim off the dead parts. Do not water just because of cold damage; water only when the soil is dry and crumbly 2 inches down, and cover plants overnight when frost is forecast.

Herbicide drift or fertilizer/pesticide burnLESS COMMON

How to tell
Suspect this if yellowing, brown edges, speckling, or distorted new growth started within a day or two of spraying nearby, using a pesticide or homemade soap spray, or applying granular fertilizer.

What to do
Stop applying sprays or fertilizer until new growth shows what is still healthy; do not use dish soap sprays. Sweep fertilizer granules off foliage, and if granular fertilizer was applied to dry soil or not watered in, water it in thoroughly; when the soil is dry and crumbly 2 inches down or baked hard and cracked, water slowly enough to moisten the root zone.

Will it recover?

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

Stopping it happening again

Grow tomatoes in full sun, mulch the soil, water deeply when the soil is dry and crumbly 2 inches down, improve drainage in wet beds, avoid wetting leaves, feed by the label, apply granular fertilizer to moist soil and water it in thoroughly, and check lower leaves often for spots.