Answer: Grass clippings should decompose in the soil without problem. The only caution about grass clippings is using them fresh as mulch over the top of the soil. Fresh grass clippings tend to clump as they dry and can effectively stop water from percolating through to the soil. But mixing them into the ground before planting should not affect your plants. New transplants sometimes go through a stressful adjustment period and yellowing leaves is one of the symptoms of stress. Usually they perk up within a week. I don't think the grass clippings have anything to do with the behavior of your plants. Try to sheild them from hot sunshine until they recover. Best wishes with your annuals.
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