Too much direct sun, especially along with unusually hot weather, can be a bad thing if you’re a ripening tomato. It’s one factor that can lead to the colour disorder shown above, which goes by names including yellow eye, yellow shoulder and green shoulder.
Some tomatoes, particularly some heirlooms, grow naturally with a bit of green at the stem end. But when it’s as pronounced as this, it’s a sign of a problem. With too much chlorophyll in the tissue, just a touch of the orange pigment carotene and almost none of the red pigment lycopene, these yellow patches will never ripen, despite the lovely red in the rest of the fruit. There is often white tissue deeper in the tomato. And the flavour and texture in the unripe portion just isn’t as… tomatoey.
This is a disappointment for home growers. You can imagine that commercial growers would find it a costly problem. It makes the tomatoes hard to process, too.
The danger time is when the tomato is close to mature size, but hasn’t begun to change colour – a process which also be delayed when the weather gets too hot. We can’t do much to avoid a major heat wave like the one we had a few weeks ago. However, on hot, hot days like that, if there is insufficient shade on the ripening fruit from the plant’s own leaves, you can temporarily shade the plants with cloth.
The best defense is to choose varieties resistant to green shoulder. These tomatoes are ‘Arkansas Traveler’ – which usually has high resistance. That these babies gave me such a “gold shoulder” is an indication of just how hot the sun was. I have to say that the rest of the fruit was quite tasty!
Soil conditions, especially with the right balance of acidity, potassium and organic matter, also contribute to green shoulder resistance or susceptibility. Precise acidulation and just-right potassium levels might be too scientific for you or me, but we can make sure our soil has plenty of organic matter.
Interested in more info on tomatoes? This article from Purdue University talks about the adverse effects of high temperatures on your not-so-red tomatoes. Other tomato defects? The excellent website Growing Tomatoes gives you tonnes (or tons, as I think it’s a U.S. site) of everything you’d want to know about, well, growing tomatoes.