Why are the leaves on my tomatoes or peppers yellowing between the veins while the veins stay green?
Interveinal chlorosis on older, lower leaves is a classic sign of magnesium deficiency — the plant is pulling magnesium from mature tissue to feed new growth.
The pattern is specific: yellow or pale green tissue between the leaf veins, while the veins themselves remain distinctly darker green. This interveinal chlorosis shows up first on the oldest, lowest leaves and moves upward as the deficiency progresses. On tomatoes and peppers it often appears mid-season when the plants are setting heavy fruit loads and pulling nutrients aggressively. The leaves may eventually turn almost entirely yellow or develop a bronze tint, and heavily affected leaves can drop.
Magnesium is a mobile nutrient, which is why deficiency symptoms appear on older leaves first — the plant cannibalizes stored magnesium from mature tissue to supply actively growing shoots and developing fruit. Sandy, acidic, or heavily leached soils tend to be low in magnesium. Excess potassium or calcium in the soil can also block magnesium uptake even when it's present, a competition effect at the root level. High-yield crops like tomatoes and peppers are especially prone to running short mid-season.
The fastest correction is a foliar spray of Epsom salt (magnesium sulfate): dissolve 1 tablespoon per gallon of water and apply to the foliage in the morning when temperatures are moderate. This gets magnesium into the plant directly without waiting for root uptake. For a soil-level fix, work Epsom salt into the root zone at 1 tablespoon per foot of plant height, watered in well. Dolomitic limestone is a longer-term soil amendment that adds both magnesium and calcium, but it also raises pH — confirm your soil pH before applying.
Foliar-sprayed magnesium sulfate tends to green up affected leaves within 7–10 days. Severely affected leaves rarely recover their original color, but new growth should come in normal once the deficiency is corrected. If symptoms keep progressing despite treatment, a soil test is worth doing — it rules out pH-driven lockout or competing ion excess, both of which require different approaches than simply adding more magnesium.
- 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.
- Gray Mold (Botrytis)Gray-brown fuzzy mold on fruit, flowers, or stems — soft, collapsing tissue beneath the coating in cool, wet conditions.
- Cabbage LooperRagged holes in brassica leaves made by a pale green caterpillar that loops its body as it moves.
- Why are the newest leaves on my plant coming in yellow while the older leaves look normal?Interveinal chlorosis appearing first on new growth points to iron deficiency — most often caused by high soil pH locking iron out of root uptake rather than iron being absent from the soil.
- Why are the edges of my older leaves turning brown and scorched-looking while the centers stay green?Marginal leaf scorch on lower, older leaves — a brown or yellowing burn along the leaf edge — is a characteristic sign of potassium deficiency, which also tends to produce weak stems and poor fruit quality.
- 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.
- Should I use fertilizer or compost — what's the difference?Compost improves soil structure and feeds slowly over the long term; fertilizer delivers specific nutrients quickly — most productive gardens benefit from both, used for different purposes.