Answer: This can be caused by too little water or it can be caused by growth to the point that the roots are crowded and they need repotting. Some plants will droop due to excess heat or excess cold exposure. Some plants will lose older leaves as the new growth increases. Without knowing which plant and how it is being grown it is a bit difficult to tell you exactly what is happening to your plants. Your local county extension might be able to help based on a more detailed understanding of what you are growing and how your greenhouse is operated.
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