Why are the lower leaves on my tomatoes turning yellow?
Lower-leaf yellowing on tomatoes is most often early blight, normal leaf senescence, or nitrogen deficiency — the pattern and timing tell you which one you're dealing with.
The lowest leaves on a tomato plant are the most likely to be affected by early blight, a fungal disease caused by Alternaria solani. It starts as yellowing, then small dark spots with concentric rings (a target-board pattern) appear. The yellowing begins on the oldest, lowest leaves and moves steadily up the plant over the season. It is almost always present to some degree by mid-summer in humid climates — it's worth managing, not panicking over.
Normal senescence — the plant simply aging and shedding lower leaves — looks similar but without the dark spots. As a tomato plant matures and fruit develops, it redirects resources upward and the lowest leaves naturally yellow and drop. This is most noticeable after the plant has been in the ground 4–6 weeks and is growing well. If the leaves above the affected zone look healthy and the spots aren't ringed, this is likely just the plant doing its job.
Nitrogen deficiency also yellows lower leaves but does so more uniformly — pale yellow-green without spots, moving upward. It often appears in plants growing in poor or sandy soil that hasn't been amended, or in plants that have been in the same container soil for many weeks. A side-dressing of compost or a dilute liquid fertilizer typically resolves it within a week or two.
The management response to early blight is mulch (prevent soil splash onto leaves), remove affected leaves as soon as they're spotted (don't compost them), and maintain consistent watering at the base rather than overhead. Copper fungicide sprays can slow the spread in severe cases but won't eliminate the disease.
- AnthracnoseSunken, dark circular lesions on ripening fruit, sometimes with salmon-colored spores in the center.
- AphidSoft, clustered insects on new growth causing curled leaves and sticky honeydew.
- Black RotV-shaped yellow lesions at brassica leaf margins with blackened veins inside — a bacterial disease that moves through the vascular system.
- Blossom End RotDark, sunken, leathery patch on the blossom end of tomato or pepper fruit — a calcium deficiency disorder.
- Brown Marmorated Stink BugSunken, corky dimples on fruit and pods caused by a mottled brown shield bug feeding through the skin.
- What are the black spots on my tomato leaves?Black or dark-brown spots on tomato leaves are usually early blight or Septoria leaf spot — two common fungal diseases with different spot patterns that are managed the same way.
- What is that black leathery patch on the bottom of my tomatoes?Blossom end rot is a calcium deficiency at the fruit level, almost always caused by irregular watering rather than a lack of calcium in the soil.
- Can you give a plant too much nitrogen, and what does it look like?Yes — excess nitrogen produces very dark green, lush leafy growth at the expense of flowers and fruit, and in high concentrations can burn roots and cause wilting.