Green and Yellow Shoulders: Why the Tops Won't Turn Red

Heat is the main cause

The shoulders of a tomato sit highest and catch the most direct sun, so they heat up the most. Extension and university sources attribute yellow and green shoulder to high temperature above roughly 90 degrees F, which prevents the production of lycopene, the pigment that makes ripe tomatoes red. At the same time, too much heat keeps chlorophyll from breaking down, so the tissue stays green. Lycopene forms best in a moderate window, generally cited around 65 to 75 degrees F, which is why heat waves during ripening produce a rash of green-shouldered fruit.

Variety, potassium, and other contributors

Heat is not the only factor. Genotype matters: some cultivars are simply prone to persistent green shoulders, while modern uniform-ripening varieties resist it. Nutrition plays a role too, with low soil potassium linked to uneven ripening and yellow shoulder, and alkaline soil pH and certain viruses have also been implicated. If the problem repeats every year on the same variety even in mild weather, the cultivar's genetics are likely the main issue rather than the weather.

What to do about it

• Keep some leaf canopy over ripening fruit so the shoulders are not baking in direct sun; avoid heavy pruning that strips the plant bare.
• Choose uniform-ripening or heat-tolerant varieties if summers routinely run above 90 F.
• Have soil tested and correct low potassium rather than guessing at fertilizer.
• Ripen affected fruit indoors off the vine and simply core out the hard shoulder, which is still edible.

Sources

Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.

• UMass Extension - Tomato, Physiological Ripening Disorders — Yellow shoulder and related ripening disorders are driven by high temperature, cultivar genetics, and nutrition; the shoulder tissue stays firm and fails to develop full color.
• UConn IPM - Yellow Shoulder on Tomato — Yellow shoulder has several causal factors including environment (high temperature over 90 F), nutrition, genotype, and virus; heat interferes with normal pigment development.
• PNW Pest Management Handbook - Tomato Yellow Shoulder / Persistent Green Shoulders — Persistent green shoulders and yellow shoulder are physiological disorders tied to high temperature and cultivar, in which chlorophyll fails to break down and red pigment does not form in the shoulder tissue.

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