Answer: Japanese Silver Trees should grow well in your gardening region so I wonder if yours suffered from drought or transplanting stress? I'd give the puny one a chance to recover. They'll need to be watered thoroughly on a regular basis until the roots become establsihed. Make sure they're not receiving reflected heat (from a nearby building or sidewalk, driveway, etc.) that might burn the foliage.
Sometimes it's difficult to thoroughly wet the soil in a planting box. You might try applying water slowly so it has a chance to trickle down and wet the entire root mass (rather than flooding the surface quickly, which may promote draining too fast for water to be taken up by the potting mix).
Hope this helps!
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