I am sorry for this delayed reply to your gardening question. We are transitioning to a new Q&A system and your question was unfortunately lost in the transition. I have discovered it now and hope this reply is not too late to be of help.
Dry soil certainly can damage roots and result in a delayed yellowing but so can saturated soil conditions. If you feel the soggy soil option is not the case with your plants then you are left with either a delayed drought symptom (which is easy to have on a fairly new plant with limited root system), or possibly to a lack of nitrogen. Nitrogen deficiency shows on older leaves first. If you saw yellow throughout the plant I might also think back to see if a weed control product such as a weed and feed fertilizer was used around the plants. If overapplied and then followed by a rainy period some can wash into the roots and damage ornamental shrubs and trees in the landscape. Time is the only solution to such damage.
Thanks for the question. Please stop in again soon!
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