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.
Potassium deficiency appears as a yellowing or browning along the outer margins of older leaves, working inward as the deficiency worsens. The leaf tip and edges scorch first; the center and veins remain green longer. The affected tissue is dry and papery, not water-soaked or mushy. Symptoms show first on the lowest, oldest leaves and progress upward. Tomato fruits from deficient plants often have uneven ripening, with green or yellow patches that don't color up normally. Pepper and bean plants may produce thin-walled, underdeveloped pods.
Potassium is mobile in the plant, so deficiency is cannibalized from older tissue first — which is why symptoms appear at the bottom of the plant. Potassium plays a central role in water regulation, cell strength, and carbohydrate transport to fruit. Sandy, light soils and soils with high rainfall or heavy irrigation leach potassium relatively quickly. High-potassium-demand crops like tomatoes, potatoes, and squash are most prone. Excess nitrogen can also suppress potassium uptake, so heavily fertilized plants showing marginal scorch are worth examining for over-fertilization as well.
Wood ash applied to the soil surface and watered in supplies potassium along with calcium, but it also raises soil pH, so it isn't appropriate for every situation — check pH before using it regularly. Greensand and kelp meal are slower-release organic options. Soluble potassium sulfate (sulfate of potash) acts more quickly and is pH-neutral. Work amendments into the root zone for best uptake. If symptoms are mild and you're mid-season, a foliar spray of soluble potassium can provide some short-term relief while soil-level corrections take hold.
A soil test is worth doing before adding potassium aggressively — excess potassium can interfere with magnesium and calcium uptake, trading one deficiency for another. Once corrected, new leaves should emerge without the scorched margins. Fruit quality on plants that experienced mid-season deficiency may still be somewhat affected; the improvement in crop quality becomes more apparent in the following season when soil levels are corrected before planting.
- 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.
- Bird DamageBerries pecked or missing, seeds scratched from beds, and seedlings dislodged — birds feeding on ripe fruit, seeds, or soil grubs.
- 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.
- 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.
- Why are the leaf edges on my plants crispy and brown after I fertilized?Crispy, scorched leaf margins after fertilizing are salt burn — excess fertilizer salts in the soil draw water out of root cells, essentially dehydrating the plant from the roots up.
- 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.
- 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.