Find the cause
If the yellow leaves are the oldest ones at the bottom, and the plant above them looks healthy, this is normal ageing and needs nothing. If yellowing is moving up the plant, appearing on new growth, or arriving with wilting or spots, work through the causes below in order.
Diagnosis helper
- Which leaves are yellow: the oldest at the bottom, the newest at the top, or all over?
- Is the soil wet or dry 5 cm (2 in) down?
- Is the yellowing even, between the veins, or around spots?
- Is one side of the plant worse than the other?
- Has the plant been fed in the last three weeks?
- Have night temperatures dropped below 10 °C (50 °F)?
Normal ageing of the lowest leaves
CommonOne or two of the oldest, lowest leaves turn evenly yellow and then brown, over a week or more. Everything above them is green and growing. Common once fruit starts to fill, because the plant moves nutrients from old leaves into fruit.
What to do
Nothing to fix. Remove the yellow leaves so they do not sit on the soil, and carry on. Removing the lowest leaves also reduces soil splash onto foliage.
Overwatering or poor drainage
CommonWidespread yellowing, often on the whole plant at once, with soil that is wet 5 cm (2 in) down. Leaves may look limp rather than crisp, and the plant wilts even though the soil is damp. In pots, check whether water actually drains out.
What to do
Stop watering until the top 5 cm (2 in) dries. Empty any saucer. In containers, check the drainage holes are not blocked; repot into a free-draining mix if the compost is waterlogged and sour. In beds, avoid watering little and often. Roots suffocating in wet soil cannot take up nitrogen, which is why the symptom looks like a feeding problem.
Underwatering
CommonYellowing with crisp brown edges, starting low, on soil that is dry well below the surface. The plant wilts in the morning as well as at midday and recovers slowly after watering.
What to do
Water deeply until it runs from the base of the pot or soaks 20 cm (8 in) into the bed, then mulch 5 cm (2 in) deep. Move to a rhythm of deep soaks rather than daily splashes.
Nitrogen shortage
CommonEven, pale yellowing that starts on the oldest leaves and moves steadily up the plant, with weak growth and small new leaves. Most likely in containers after six weeks or more without feeding, or in poor soil.
What to do
Feed with a balanced liquid fertiliser now, and again in two weeks. Do not switch to a high-nitrogen feed once flowering has started: it delays fruit. If the plant is flowering, use a tomato feed and accept slightly slower recovery.
Magnesium shortage
PossibleYellowing between the veins while the veins themselves stay green, on older leaves first. Common in containers and in heavily fed plants, because high potassium feeds compete with magnesium uptake.
What to do
A foliar spray of Epsom salts (about 1 tablespoon in 4 L, 1 gal, of water) greens leaves within a week or two. It treats the symptom; long term, use fresh compost each season and avoid overfeeding with potassium.
Early blight or septoria leaf spot
PossibleYellowing around distinct spots, not uniform. Early blight makes dark spots with concentric rings; septoria makes many small round spots with pale centres and dark edges. Both start on the lowest leaves and move up, worse in wet weather.
What to do
Remove affected leaves and bin them, do not compost. Mulch to stop soil splashing onto leaves, water at the base only, and improve airflow by spacing and removing lower foliage. Neither is usually fatal, but both spread if leaves stay wet.
Fusarium or verticillium wilt
PossibleYellowing and wilting on one side of the plant, or on one side of individual leaves, that does not recover overnight. Cutting the main stem lengthwise near the base shows brown streaking inside.
What to do
There is no cure. Remove and bin the plant. Do not grow tomatoes, potatoes, peppers or aubergines in that soil for at least three years, and choose varieties with resistance codes on the packet next season. In containers, discard the compost.
Late blight
PossibleGrey-green then brown patches, often with a pale halo, spreading fast in warm humid weather, with dark streaks on stems and firm brown mottling on fruit. Days, not weeks, from first sign to a dead plant.
What to do
Remove and bin the whole plant immediately, including fallen leaves, to protect nearby plants and any potatoes. Do not compost. Next season, grow resistant varieties and keep plants under cover where you can.
Cold damage
PossibleYellowing, sometimes with a purple tinge to leaf undersides, after a run of nights below 10 °C (50 °F), usually soon after planting out. Growth stalls at the same time.
What to do
Cover with fleece on cold nights. The plant grows out of it as soon as nights warm, but expect a week or two of slow growth. Do not feed to compensate; the roots are not taking up much anyway.
Root damage from hoeing or transplanting
RareYellowing and wilting a few days after weeding close to the stem, moving a plant, or a root-bound seedling going into the ground.
What to do
Water in, shade for a couple of days, and leave the plant alone. Mulch instead of hoeing near the stem in future.
Herbicide contamination
RareYellowing with distorted, twisted, fern-like new growth and cupped leaves. Usually traced to manure or compost containing aminopyralid residue, or spray drift from a neighbouring lawn treatment.
What to do
Plants rarely recover fully. Do not use that compost or manure on food crops again. Repot into clean compost where you can, and test suspect compost next time by sowing beans in it before using it widely.
Recovery
Watering and feeding problems show improvement in new growth within one to two weeks, though the already-yellow leaves will not turn green again. Cold damage clears once nights warm. Leaf-spot diseases stop spreading once leaves stay dry, but affected leaves do not recover. Wilt diseases and herbicide damage do not recover at all.
Prevention
Mulch 5 cm (2 in) deep to keep soil moisture even and stop rain splashing soil onto leaves. Water at the base, in the morning, deeply and less often. Space plants 45 cm (18 in) apart for airflow, and remove the lowest leaves once the plant is established. Feed containers weekly once flowering starts, and start each season in fresh compost. Rotate beds so tomatoes and potatoes do not follow each other.
Frequently asked questions
Should I remove yellow tomato leaves?
Yes. They contribute almost nothing and can harbour disease. Remove them cleanly at the stem, and bin rather than compost any that carry spots.
Will yellow leaves turn green again?
No. A leaf that has lost its chlorophyll does not recover. Judge whether your fix worked by the colour of new growth.
Is it normal for the bottom leaves to yellow?
Yes, especially once fruit is filling. The plant is moving nutrients from old leaves into the crop.
Can overwatering cause yellow leaves?
It is one of the most common causes. Wet soil starves roots of oxygen, so they stop taking up nitrogen and the leaves go yellow even though the plant has plenty of water.
Do I need to throw the plant away?
Only for wilt diseases and late blight. Everything else on this page is treatable or normal.
Sources
- How to grow tomatoes (opens in a new tab) Royal Horticultural Society
- Growing tomatoes in home gardens (opens in a new tab) University of Minnesota Extension
- Nutrient deficiencies and leaf symptoms (opens in a new tab) Clemson Cooperative Extension