Tomato Leaves Turning Yellow
"Why are my tomato leaves turning yellow" almost always needs a follow-up question: where on the plant, and where on the leaf? Yellowing that starts at the bottom of the plant points somewhere very different from yellowing that shows up on new growth, or right after transplanting — the position is often more informative than the color itself.
Possible Causes
- Natural lower-leaf yellowing as the plant matures and redirects energy upward — normal if it stays limited to the oldest, lowest leaves
- Nutrient deficiency (commonly nitrogen or iron) — nitrogen tends to show on older leaves first, iron on newer growth
- Transplant shock or root disturbance in the days right after moving the plant
- Overwatering or poor drainage limiting how much the roots can take up
- A fungal or bacterial disease affecting the roots or stem, especially if yellowing comes with wilting or spots
What to Check
- Where the yellowing is — bottom of the plant, top, or all over
- Whether it's between the veins or across the whole leaf
- Timing — did it start after a recent transplant or a change in watering?
- Any other signs alongside it — spots, curling, wilting
Want a real answer for your plant?
The causes above are a starting point, not a diagnosis — they don't replace looking at your actual plant. Upload a photo for an analysis based on the real symptoms.