The yellow leaves could point to several different causes. I suspect that you are referring to older leaves as opposed to new leaves at the end of the branches. If I am not correct about this please submit another question with details to the Monrovia website.
Yellowing and drop of older leaves is most likely due to transplant shock...especially if you planted in the last few weeks. The plants will get over it with good care and time. Other causes of these symptoms on established plants include dry or soggy wet soil conditions for a period of time. Again good care and alleviation of the soil moisture extreme will help the plants turn around and resume normal growth.
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