I would add some more mulch and increase the amount of water per watering per plant to something like 1 to 1.5 gallons, whatever is appropriate to keep the soil moist at a depth of 8" soon as you finish watering. Also, make sure that they are getting morning sun or dappled sun. Maybe even full but bright shade. That prevents sunburn on the leaves in the summer. Down here in Tx, morning sun is a must but in the northeast, in some places you can actually grown them in full sun.
If you notice that the blooms are browning or if leaves are browning from the edges inwards, they need more water. When watering, add water from the crown outwards and try to water the soil, never the leaves in order to minimize the chances of fungal infections.
The dried out stems can be pruned all the way down if they do not leaf out by the end of May.
Some mechanical injuries will produce purpleish leaf spot. But more common in late Summer is cercospora leaf spot. There is no fungicide that can cure it but it is made worse by overhead watering so watering the soil and picking up plant debris that has fallen helps a lot. It can be caught at the plant nursery or in our gardens. It is more common to see the brown/purpleish spots as the end of summer or start of Fall arrive. More rain during that time makes it worse but less rain makes the symptoms less obvious. I usually cut any leaves that look ugly at the petiole string.
More info:
http://www.aces.edu/pubs/docs/...
Does that help you?
