Answer: I would suspect it is moisture stress due to the summer heat and dryness this year. New plants are more susceptible to this because they are not yet fully rooted. This late in the season there is nothing you need to do, except water if there is a long dry spell. When you water, water slowly and deeply to encourage deep rooting. To know if you need to water, dig into the soil with your finger. If it is still damp, don't water yet. Also maintain a good mulch layer over the root area, it should be several inches thick and spread out flat.
Q&A Library Searching Tips