The top of my olive topiary is losing leaves and very scrawny. What are possible causes?

Question

I have 2 topiaries in planters for about 2 years. They did fine but this year the top ball appears to be dying (leaf yellowing and loss) while the bottom ball is robust and green. No sign of bugs or fungus. One is worse than the other but both are showing the same signs.

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Answer 1

The signs are consistent with water deficit (drought stress). I understand it's been a hot summer in SoCal. Check water needs with a soil moisture meter, don't guess.

https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-moisture-in-plants.htm