Problem of vinca flowers

Question

I’m Turkish. I couldn’t find the answer in my country. I’m sorry if I can’t write it correctly. I had vinca flowers. It was very healthy in the summer. the Leaf of flowers was yellow At the beginning of autumn. My city is 35 degrees in autumn. my city is 45 degrees in summer.
Some of the plants died. plants  I trim were alive, but it stopped growing. The stem and root of the plant were intact. The problem is the leaves. Everyone has this problem. Everyone’s flower (vinca Flowers) gets sick in the autumn.
I sent two photos for example. What is name of problem? thank you very much

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Answer 1

If the soil is too alkaline you can have a problem with uptake of iron. Yellowing also can be caused by lack of nitrogen. Try using a fertilizer with iron, nitrogen and sulfur to balance the pH and replace lost nutrients.

https://www.gardeningknowhow.com/ornamental/flowers/annual-vinca/vinca-is-turning-yellow.htm